Instrument Flying

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Ground School

Chapter 1: Instrument Flight

1.1 Introduction to Instrument Flying

The ability to depart an airport, enter the clouds, and emerge in front of a distant runway is a remarkable thing. Welcome to your journey as an instrument pilot.

Instrument flying is the ability to fly an aircraft using only the instruments in the cockpit, instead of visual references like the horizon. It's an important skill for pilots because it allows them to fly safely in conditions with limited visibility, such as: clouds, storms, turbulence, and fog.

Instrument flying is governed by Instrument Flight Rules (IFR), which include:
- Procedures for low-visibility conditions
- Use of radio beacons and GPS
- Efficient routes to reduce fuel costs and flight times

Some fundamental skills of instrument flying include:
- Instrument cross-checking
- Instrument interpretation
- Aircraft control.

1.2 Basic Attitude Instrument Flying

Instrument flying starts with learning to control the airplane solely by reference to flight instruments. This is basic attitude instrument flying.

Basic attitude instrument flying (BAI) is the ability to control an aircraft without using visual references, but instead by using the aircraft's instruments. It's the most important instrument flying skill and is taught early in instrument rating training.

Here are some tips for BAI:
- Develop a scan pattern
- Group instruments by the information they provide
- Create the conditions needed for each phase of flight
- Use fine inputs for precise control
- Keep the wings level for heading corrections of five degrees or less
- Change the power to intentionally change airspeed in level flight
- Start to level off about 10 percent of the rate of climb before reaching the desired altitude

1.3 Departure Procedures

Every instrument flight has a departure procedure, even if it's a standard climb gradient in any direction. Let's dive into the first phase of an instrument flight.

Aircraft departure procedures are a series of routes that guide an aircraft from the runway to the en route phase of a flight. They are designed to provide obstacle clearance and make air traffic operations more efficient.

There are several types of departure procedures, including:
Standard Instrument Departure (SID): A published flight procedure that is typically used for IFR flights at large airports. SIDs are printed graphically and are developed to accommodate as many aircraft categories as possible.
Obstacle Departure Procedure (ODP): A type of departure procedure.
Visual Climb Over Airport (VCOA): A type of departure procedure that requires a climb in visual conditions to a certain altitude.
Vectors: A type of departure procedure.
Air traffic control assigns a departure procedure to an aircraft, and the aircraft cannot fly it without clearance.

1.4 Enroute Procedures

The largest portion of an IFR flight is the en route phase. It's important to understand the unique aspects of the en route phase of flight.

Aircraft en route procedures are the flight standards and guidelines that govern the segment of a flight between the departure and arrival procedures. These procedures are established by the FAA and other organizations, and include:
- Flight levels: Aircraft must be flown at flight levels at or above the transition levels or the lowest usable flight level.
- Obstacle clearance: Obstacle clearance criteria are established for different areas.
- Navigation: Navigation performance standards are established.
- Communications: Communications requirements are established, including direct communications between controllers and pilots.
- Air traffic control: Air traffic control services are provided for aircraft on IFR flight plans.

Pilots must maintain a high level of operating skill during the en route phase of flight. Some background knowledge that is useful for en route procedures includes:
- The functions of the GPS receiver's navigation mode
- The symbology on the moving map display screen
- The track bar sensitivity parameters in NAV mode

1.5 Arrival & Approach Procedures

While standard arrival procedures are less common for light airplanes than large airplanes, you may encounter them. We will cover approaches later in the course, but here we’ll review aspects of routing to the initial approach.

Aircraft arrival and approach procedures are a series of predetermined maneuvers that ensure safe flight and orderly air traffic.

The procedures include:
Arrival segment
The transition from en-route to approach flight, starting at the latest en-route point and ending at the initial approach fix (IAF). A standard terminal arrival route (STAR) is a type of arrival segment published on charts.
Instrument approach procedure (IAP)
A series of maneuvers that guide the aircraft from the initial approach fix to a point where a landing can be completed. There are several types of IAPs, including non-precision approach (NPA), approach procedure with vertical guidance (APV), and precision approach (PA).
Missed approach procedure (MA)
A procedure that provides protection from obstacles during a missed approach. It usually starts at the missed approach point (MAPt) and ends at a specified point or altitude.

Chapter 2: Instruments and Systems

2.1 The Airspeed Indicator

Airspeed is lifeblood of flying. This lesson covers how the instrument works. An airspeed indicator (ASI) is a flight instrument that measures the speed of an aircraft relative to the air. It's a differential pressure gauge that compares the pressure of moving air (ram pressure) to the pressure of still air (static pressure). The difference in pressure is displayed on the ASI as airspeed in units like miles per hour (mph), knots (kt), or kilometers per hour (km/h).

The ASI is part of the aircraft's pitot-static system, which also includes static ports and static vents. The static ports and static vents measure static pressure, which is used as a baseline to compare against the dynamic pressure from the pitot tube. The higher the difference in pressure between the pitot tube and static port, the faster the plane is moving.

Some important airspeed limitations are not marked on the ASI, but can be found in the AFM/POH or on placards.
What it does
Measures the speed of an aircraft through the air
How it works
Compares the pressure from the pitot tube to the pressure from the static port to determine airspeed
What it displays
Speed in miles per hour (MPH), knots (kn or kt), kilometers per hour (km/h), or meters per second (m/s)
Purpose
Provides guidance during climbs, descents, and landings
Accuracy
Highly accurate when properly calibrated

2.2 Basic Altimetry

The altimeter is an instrument that measures the pressure of the air around the aircraft and indicates this as a number that represents altitude. It measures the altitude of an object above a fixed level, such as sea level. Altimeter is an important navigation tool for pilots.

Here are some key points about altimeters:
Barometric altimeters
These altimeters use aneroid capsules that expand or compress in response to changes in static pressure. The capsules are linked to a pointer that moves across a dial calibrated in feet or meters.
Pressure settings
The altimeter's sub-scale and pressure setting control allow the pilot to calibrate the altimeter to indicate the correct flight level or altitude. The barometric pressure setting determines the datum used to indicate the aircraft's elevation.
Altimeter safety
Proper altimeter settings are essential for safe separation from the ground and other aircraft.

2.3 Turn Indicators / Coordinators

Although there are some variations in the type, there is always an instrument in the airplane that measures the rate of heading change through the horizon. Turn indicators and turn coordinators are aircraft flight instruments that help pilots control and execute turns:

Turn indicator
Shows the rate of turn, or the rate at which the aircraft's heading changes. The turn indicator is usually a plane silhouette that dips when the aircraft turns.
Turn coordinator
A gyroscopic instrument that combines a turn indicator with a balance indicator, or slip indicator, to show the rate of turn and the coordination of the turn. The balance indicator is usually a ball in a tube that remains in the center during a coordinated turn. If the ball moves to the outside of the turn, the aircraft is skidding.

2.4 The Vertical Speed Indicator

The Vertical Speed Indicator provides information about the initial trend and then, a moment later, the rate of climb or descent. How it accomplishes this is quite remarkable. A vertical speed indicator (VSI) shows how fast an aircraft is climbing or descending, or changing altitude. It's also known as a rate of climb indicator, variometer, or vertical velocity indicator.

Here's how a VSI works:
Air pressure
The VSI measures the difference between the current static pressure and the static pressure a few seconds ago.
Components
The VSI contains a flexible metal diaphragm that's connected to the static air source, and a small hole called a calibrated leak that connects the VSI casing to the static source.
Display
The VSI displays the rate of climb or descent in feet or meters per minute on a circular scale or needle, or on a ribbon in an electronic flight instrument system (EADI).
Lag
There's a brief delay between the actual change in rate and the display of that change.
Reset
When the aircraft is in level flight, the calibrated leak dissipates the air in the diaphragm, resetting the VSI to zero.

The VSI works with the airspeed indicator to help pilots maintain control during level flight.

2.5 Pitot/Static System

The Pitot/Static system uses the air pressure to provide information to your airspeed indicator, altimeter, and vertical speed indicator. It's important to understand how this simple system works.

A pitot–static system is a system of pressure-sensitive instruments that is most often used in aviation to determine an aircraft's airspeed, Mach number, altitude, and altitude trend. A pitot–static system generally consists of a pitot tube, a static port, and the pitot–static instruments.
How it works
The system measures two types of air pressure:
- Ram air pressure: The impact pressure that enters the pitot tube through a small hole
- Static air pressure: The ambient air pressure around the aircraft, measured by static ports attached to the fuselage
What it measures
The pitot-static system provides data on flight parameters such as:
- Altitude
- Airspeed
- Mach number
- Vertical speed
How it is used
The data is displayed on calibrated instruments, such as the altimeter, airspeed indicator, and vertical speed indicator
Safety
Errors in pitot-static system readings can be dangerous, and have been a factor in commercial airline disasters. The aircraft to have their pitot-static systems inspected and tested every two years or before.

2.6 Pitot/Static Icing, Errors, and Blockages

As an instrument pilot, it's extremely important that you recognize signs of blockages in the Pitot-Static system and know what to expect from your flight instruments.

Pitot/static system errors can occur when there are issues with the pitot tube or static ports in an aircraft's flight instruments. These errors can cause the instruments to provide false information, which can lead to a loss of control.

Blocked pitot tube
This can cause the airspeed indicator to read incorrectly:
- Climbing: The airspeed indicator will increase even if the aircraft's actual airspeed is constant. This is because the pressure in the pitot system remains constant while the atmospheric pressure decreases.
- Descending: The airspeed indicator will decrease.
- Zero airspeed: If the pitot tube is clogged and its drain hole is open, the airspeed will remain at zero.

Blocked static port
This can cause the altimeter and vertical speed indicator (VSI) to remain frozen:
- Altimeter: The altimeter will report the pressure trapped in the static system.
- VSI: The VSI will move to 0 FPM and no longer change.
- Airspeed indicator: The airspeed indicator will read lower than actual airspeed when flying above the altitude where the static port became blocked, and higher than actual airspeed when flying below.
To prevent icing, many pitot tubes have a heating element.

2.7 The Vacuum System

This lesson describes common engine-driven vacuum systems that power some of the airplane's gyroscopic instruments.

An aircraft's vacuum system powers the gyroscopes in flight instruments, which helps the aircraft sense its attitude and heading.

The system typically includes:
- Vacuum pump: An engine-driven pump that creates suction by drawing air through a filter
- Regulator and filters: Regulates and filters the air
- Instruments and accessories: Includes the gyroscopes and other instruments that use the vacuum
- Hoses or tubing: Connects the pump, regulator, filters, and instruments

The vacuum system works by spinning a rotating wheel with cups, which is governed by the amount of vacuum supplied to the instruments. The vacuum pressure required for instrument operation is usually between 4.5 inHg and 5.5 inHg.

Here are some tips for maintaining your aircraft's vacuum system: Change the filters at recommended intervals, Specify low-restriction vacuum system fittings, Change the hoses every 10 years, and Monitor the vacuum pressure during flight.

2.8 The Electrical System

In airplanes the electrical system is independent from the ignition system. It is important to understand the basic elements.

An aircraft's electrical system is a network of components that generates, distributes, and stores electrical power for the aircraft to operate. It's a vital part of all but the simplest aircraft designs.
- Generators and alternators: Convert mechanical energy from the aircraft's engines into electrical energy
- Voltage regulator: Maintains a consistent voltage to prevent damage to electrical components
- Electrical distribution bus: Connects the batteries in each module and distributes power
- Master switch: Controls the flow of power to aircraft systems
- Ammeter or loadmeter: Confirms the health of the system and indicates whether the battery is charging normally
- Switches, fuses, & circuit breakers: Turn components on and off, and protect them from excess current
- Battery: Provides electrical power when the alternator or generator is not available

The electrical system powers many functions on the aircraft, including: propulsion, lighting, instrumentation, and navigation.

2.9 De-icing/Anti-Icing Systems

Learn the essentials of aircraft de-ice and anti-ice systems! We’ll cover how these systems operate and protect our aircraft’s aerodynamic surfaces. Ice buildup can degrade an aircraft's performance and handling characteristics.

Aircraft de-icing and anti-icing systems prevent or remove ice from aircraft surfaces to maintain aerodynamic characteristics and ensure safe flight:
Anti-icing systems
Prevent ice from forming on aircraft surfaces, such as wings and engine intakes, before the aircraft enters icing conditions. Anti-icing systems typically use heat to evaporate liquid water, and can use engine bleed air, electrical power, or a combination of both.
De-icing systems
Remove ice from critical aircraft surfaces after it has formed. De-icing systems can use a variety of energy sources, including mechanical, electrical, and thermal.

Chapter 3: Regulations

3.1 Regulations

This lesson reviews the structure of the regulations that govern aviation in the world. [Ex: Civil Aviation Act, Sri Lanka]. Understanding this structure will help you when you need to find the answer to a regulation question.

Aviation regulations are a set of rules that ensure the safety, security, and efficiency of air travel. These regulations cover a wide range of areas, including:
- Aircraft operations
- Airworthiness
- Airport infrastructure
- Pilot licensing
- Air traffic management
- Environmental protection
- Passenger rights
- Liability in cases of accidents or incidents

Aviation regulations are created and maintained by aviation authorities, such as the International Civil Aviation Organization (ICAO). The ICAO sets Standards and Recommended Practices (SARPs) that member states are encouraged to adopt.

3.2 Basic Med

This lesson covers the rules surrounding "Basic Med", which is an option for healthy pilots if they've held an aviation medical at any point before.

Aviation medicine is a medical specialty that focuses on the health and safety of people who fly, including:
Crew and passengers
Aviation medicine is concerned with the health and safety of those who fly, including pilots, cabin crew, and passengers.
Aviation license holders
Aviation medicine is concerned with the selection and performance of those who hold aviation licenses.
Public health
Aviation medicine helps mitigate and manage health risks and other public health events, such as communicable diseases, radionuclear accidents, and chemical accidents.

3.3 Flight Rules

This lesson looks at flight rules, which defines all of the flight rules that pilots must adhere to while in the air as per Sri Lanka Civil Aviation Act.

Aviation flight rules are regulations and procedures that govern the operation of aircraft in various conditions. They are designed to ensure the safety and efficiency of air traffic.

Some types of flight rules include:
Instrument flight rules (IFR): Used when flying in conditions where visual reference is not safe, such as between cloud layers. IFR flight involves using the aircraft's instruments for navigation and electronic signals for guidance.
Visual flight rules (VFR): Used when flying in weather conditions that are generally clear enough to allow the pilot to see where the aircraft is going.
Night visual flight rules: Used when flying primarily by visual reference at night.

Other rules that apply to all aircraft include:
- Displaying anti-collision and navigation lights
- Using Coordinated Universal Time (UTC)
- Obtaining an air traffic control clearance for controlled flights

The pilot-in-command is responsible for operating the aircraft in accordance with the rules.

3.4 IFR Equipment

This lesson looks at rules, which prescribes all of the equipment that is required on aircraft operating in the National Airspace.

Aircraft that fly under Instrument Flight Rules (IFR) require a specific set of equipment, including:
Flight instruments: Airspeed indicator, altimeter, magnetic direction indicator, gyroscopic rate-of-turn indicator, slip-skid indicator, gyroscopic pitch-and-bank indicator, and gyroscopic direction indicator
Other instruments: Vertical speed indicator, free-air temperature indicator, heated pitot tube, power failure warning device, and alternate source of static pressure
Safety equipment: Safety belts, Emergency Locator Transmitter (ELT), position lights, anticollision lights, and landing lights
Communication equipment: Two-way radio communication system and navigation equipment
Spare parts: One spare set of fuses, or three spare fuses of each kind
Lights: Lights for night operations

IFR regulations provide pilots with procedures for flying in low visibility conditions. Pilots must be proficient in using the required equipment and be familiar with all IFR requirements before taking off.

3.5 Rules For IFR

This lesson will look at the regulations that apply specifically to the instrument pilot as per Sri Lanka Civil Aviation Act.

Aircraft operating under Instrument Flight Rules (IFR) must meet certain requirements to ensure safe flight:
Equipment: Aircraft must have specific instruments, radios, and navigation systems. Some required instruments include a gyroscopic rate-of-turn indicator, slip-skid indicator, oil temperature gauge, and oil pressure gauge.
Maintenance: Aircraft must be maintained to strict guidelines.
Communication: Aircraft must have reliable radio communication systems to communicate with Air Traffic Control (ATC).
Weather: Pilots must have accurate weather information and continuously check weather forecasts.
Flight plan: Pilots must update their flight plans as needed.
Pilot proficiency: Pilots must be proficient in using the required equipment.
IFR rating: Pilots must meet certain IFR rating requirements, including a minimum number of hours of flight time.

IFR is one of two sets of regulations that govern civil aviation aircraft operations, the other being visual flight rules (VFR). IFR is used when it's not safe to fly using visual references, such as when flying through clouds, fog, or heavy rain.

3.6 Operations Below the DA/MDA

It is an important to know the regulation because it defines the requirements that must be met to continue an approach below the DA/MDA. You must be familiar with this regulation to fly under IFR.

Aircraft operations below the Decision Altitude (DA) or Minimum Descent Altitude (MDA) are not permitted unless certain conditions are met:
- The aircraft is able to descend normally to the runway
- Flight visibility is at least the minimums specified in the standard instrument approach

At least one of the following visual references is clearly visible and identifiable:
- The approach light system
- The threshold
- The threshold markings
- The threshold lights

The MDA is the lowest altitude an aircraft can descend to during the final approach segment of an instrument approach procedure. It's used to create a safety buffer between the aircraft and terrain or obstacles.
The DA is the altitude at which a pilot must make a decision to continue landing or initiate a missed approach. Pilots may descend slightly below the DA when making this decision.

3.7 Lost Communication Procedures

This is the regulation that prescribes the actions you should take if you lose communication with ATC. In this lesson, you will learn the steps to follow should you find yourself in this situation.

Aircraft lost communication procedures are a set of actions pilots take to maintain safety and control of an aircraft if they lose radio contact with air traffic control (ATC):
Establish Unicom contact
Pilots try to establish contact with ATC using Unicom frequencies or other available communication channels. Unicom is a common frequency used for non-towered airports.
Follow assigned route and altitude
Pilots continue to fly the last assigned route and altitude unless it's necessary to deviate for safety reasons.
Set transponder to lost communication squawk code
Pilots set their aircraft's transponder to a specific squawk code to alert other aircraft and radar facilities of the communication failure. For example, the emergency code 7600 is used to indicate radio issues.
Comply with published procedures
Pilots follow the lost communication procedures outlined in official aviation documents, such as Aeronautical Information Publications (AIPs) or Standard Operating Procedures (SOPs).
Stay predictable
Pilots try to remain predictable so that ATC can accommodate traffic around them.
Check frequency selection, headset connections, stuck mike, and volume control
Pilots check these things to see if they might be causing the communication failure.

3.8 Required IFR Reports

From the student's perspective, the long list of required IFR reports is rather arbitrary, yet it's extremely important. The best device to memorize and be able to recall this list as per AIP ENR 1.10-1 Sri Lanka.

Aircraft operating under Instrument Flight Rules (IFR) must report certain events to Air Traffic Control (ATC) or Flight Service Station (FSS):
Unforeseen weather: Report any unanticipated weather conditions
Altitude changes: Report when changing altitudes, including when leaving a previously assigned altitude or flight level
Airspeed changes: Report if the average true airspeed at cruising altitude varies by 5% or 10 knots
Holding fix: Report the time and altitude when reaching a holding fix
Position reports: Send position reports unless ATC advises that the plane is in radar contact

Chapter 4: Weather

4.1 Air Masses and Fronts

Air Masses have specific properties. They can be warm, cold, low pressure, or high, and as they interact around the Earth, the zones where they interact are called fronts. Understanding this is central to understanding the big weather picture.

Air masses and fronts are atmospheric features that affect weather and can impact aviation:
Air masses
Large bodies of air with similar temperatures and humidity. Air masses are named based on where they form, such as maritime, continental, polar, or tropical. The characteristics of an air mass determine the weather it produces and how it interacts with other air masses.
Fronts
The boundaries that form when air masses meet. Fronts are identified by temperature changes based on the motion of the air masses. The four types of fronts are:
- Cold fronts: A colder air mass displaces a warmer air mass, bringing cooler temperatures, rain, and thunderstorms.
- Warm fronts: A warmer air mass displaces a cooler air mass, bringing warmer temperatures and rain.
- Stationary fronts: Warm and cold air meet but neither displaces the other, resulting in persistent rain.
- Occluded fronts: Warm air is sandwiched between two cold air masses, causing heavy precipitation.

4.2 Atmospheric Stability

When we talk about atmospheric stability, we are referring to the stability of the air vertically; would a parcel of air have a tendency to rise and if so, how fast and how far?

Atmospheric stability is a measure of how much the atmosphere resists vertical air movement. It's important for pilots to understand atmospheric stability, especially for glider pilots.

Explanation
In a stable atmosphere, air resists moving up or down. In an unstable atmosphere, air can move up or down more easily, and disturbances can grow into vertical currents.

Factors that affect atmospheric stability include:
Temperature lapse rate: The rate at which temperature decreases with height
Saturation: The amount of moisture in the air
Local heating and cooling: How the air is heated or cooled in a specific area
Surface wind: The wind at the surface
Air mass characteristics: The characteristics of the air mass

An unstable atmosphere can lead to: Significant turbulence, Vertical clouds, and Severe weather.

4.3 Thunderstorms

Thunderstorms are one of the biggest weather hazards to pilots. How they form is quite simple. Understanding this process will help you avoid them.

Thunderstorms are a major hazard to aircraft operations, and can create a number of risks for pilots, including:
Turbulence: Thunderstorms can create severe turbulence, which can be dangerous for aircraft.
Icing: Thunderstorms can cause icing on aircraft.
Lightning: Thunderstorms can produce lightning, which can strike aircraft. However, aircraft are designed to withstand lightning strikes, and the odds of a lightning strike are low.
Hail: Thunderstorms can produce large hail, which can be dangerous for aircraft.
Squalls: Thunderstorms can generate squalls or gust fronts, which can cause severe low-level turbulence.
Downbursts: Thunderstorms can produce downbursts, which can be dangerous for aircraft.
Cloud bases: Cloud bases in thunderstorms can change rapidly and be very low, making it hazardous to fly beneath the cloud.

Pilots should use weather forecasts and SIGMETs to plan their flight around thunderstorms. Jet aircraft can usually fly safely over thunderstorms if they stay well above the turbulent cloud tops. En-route flights will often try to go around the most intense and turbulent storms, which are usually the tallest.

4.4 Low-Level Wind Shear

Low-level windshear has been identified as a contributing factor in several significant incidents, as documented by flight data recorders. Windshear is characterized as a shift in wind direction and/or speed occurring over a relatively short distance in the atmosphere.

Low-level wind shear (LLWS) is a sudden change in wind speed or direction within the lowest 2,000 feet of the atmosphere. It can occur in the vertical, horizontal, or both planes. LLWS can be caused by a number of factors, including: Thunderstorms, Heavy rain, Low-level temperature inversions, and Buildings or trees near the runway.

LLWS can be a severe threat to flight safety, especially during takeoff and landing. It can cause a sudden loss of lift, speed, and altitude, which can lead to a loss of control and a fatal accident.
To help pilots respond appropriately, ground-based Low Level Wind Shear Alert Systems (LLWAS) detect wind shear and related weather phenomena and provide real-time warnings. Pilots should be aware that LLWS can cause dramatic shifts from headwind to tailwind, which can lead to a decrease in airspeed, a pitch down, and a decrease in altitude.

4.5 Relative Humidity and Dew Point

Relative Humidity and Dew Point are important concepts in understanding water in the atmosphere and how and when it condenses into clouds and fog.

Relative humidity (RH) and dew point are both measurements of moisture in the air, but they serve different purposes:
Relative humidity
A relative measurement of how much moisture is in the air compared to its maximum capacity. RH is directly related to temperature, so cooler days feel drier even if the RH is the same.
Dew point
An absolute measurement of how much water the air contains. It's the temperature at which air needs to be cooled to reach 100% RH, when the air can no longer hold water as a gas. If the air is cooled further, water vapor will condense into liquid, usually as fog or precipitation.

Here are some ways that RH and dew point are used in aviation:
- Carburetor icing and fog
General aviation pilots use dew point data to calculate the likelihood of these occurring.
- Cumuliform cloud base height
Pilots use dew point data to estimate the height of a cumuliform cloud base.
- Visibility
Pilots pay extra attention to RH and dew point when visibility is marginal. For example, if the temperature and dew point are close, fog can appear around the airport as the ground radiates heat and cools the air.

4.6 Fog

Understanding where and when fog might form will help you make better weather decisions. It's pretty simple. In this lesson, you learn the different types of fog and how they form.

Fog is a natural occurrence that happens when cold air from an airplane's air conditioning system mixes with the warmer, humid air inside the cabin. This lowers the temperature to the dew point, causing water droplets to form and appear as fog or clouds.

Fog is most likely to occur on hot, humid days, and is more common in tropical airports. It's usually short-lived because the cooled air quickly warms above the dew point.

Fog can also be a hazard for pilots landing in low visibility. Pilots must be trained to use the aircraft's automated systems to land in fog, such as the instrument landing system (ILS). The ILS uses radio beams from metal poles at the end of the runway to help guide the aircraft. Pilots must also be able to use transmissometers, which measure light every 15 seconds, to determine if they have enough visibility to land.

4.7 Icing

Though not in Sri Lanka, icing is one of the major hazards of instrument flight. Knowing how and where ice forms is critical to operational safety.

Aircraft icing is the accumulation of ice on an aircraft during flight or on the ground. It can occur when supercooled water droplets freeze on the aircraft's surfaces, such as the wings, tail, and engines.

4.8 Clouds

Learning to read the clouds is an important skill for a pilot. In this lesson, you begin to develop that skill by learning different cloud types and which types of systems they are associated with.

Different types of clouds can have different effects on aircraft, including:
Cumulonimbus clouds: Also known as thunderstorm clouds, these clouds can be extremely dangerous to air traffic. They can produce severe turbulence, icing, thunderstorms, and hail. Pilots will try to avoid flying through these clouds, or will fly above them in larger passenger aircraft.
Cumuliform clouds: These clouds can produce turbulence and icing. Even small groups of cumulus clouds can be a warning sign for turbulence. Pilots should also watch for the development of clear, mixed, and rime ice.
Low clouds: These clouds can have a negative effect on flights, including take-off, landing, and the flight itself. Low clouds can also influence cargo flights and construction helicopters.
Cirrus clouds: These clouds crisscross the sky above an airplane.
Jet contrails: These crisscross the sky around the aircraft.

Clouds can affect aircraft in several ways, including:
- Turbulence: Clouds can create turbulence, which can make for a bumpy ride. This is because clouds are cooler than the air around them, which creates a "pothole" in the sky.
- Low visibility: Low clouds can make it difficult to see during landing.
- Flight planning: Pilots must know the cloud ceiling to plan their flights, avoid collisions, and comply with regulations. The cloud ceiling is the height of the lowest layer of clouds that cover more than half of the sky.
- Other hazards: Clouds can contain hazards like updrafts and downdrafts.

4.9 Temperature Inversions

Temperature Inversions are anomalies that occur in the atmosphere and create some unique and predictable weather conditions.

Temperature inversions occur when the air at higher altitudes becomes warmer than at lower altitudes. They can be caused by nocturnal inversions, which occur when there are clear skies and calm or light winds near the surface, or frontal inversions, which occur when a warm front is present and cold, dense air settles in just north of the warm front.

Temperature inversions can negatively affect aircraft performance in a number of ways, including:
Lower air density
This results in a lower indicated airspeed, which requires the pilot to reduce the climb path angle to regain speed.
Higher temperature
This reduces engine performance.
Sudden wind speed changes
Inversion layers separate the air above and below, which can cause pilots to experience a sudden change in wind speed when crossing them.
Significant wind shear
When combined with high winds from the low-level jet stream, a temperature inversion can produce significant wind shear close to the ground.

Chapter 5: Weather Sources

5.1 Overview

Weather Services describes the products pilots use to understand the weather. You should be aware of how to find this information regardless of what product you use.

Pilots should gather all information vital to the nature of the flight prior to every flight. They can receive a regulatory compliant briefing without contacting Flight Service.

5.2 Weather Briefings

Establishing a ritual around gathering weather information is critical to your safety. In this lesson, we review the 3 types of briefings.

Standard briefing – Offers an in-depth look at your flight plan, including current conditions and forecasts.
Outlook briefing – Useful for understanding weather trends when planning a flight several days in advance.
Abbreviated Briefing – Provides updates to a previous briefing or specific information upon request.

Weather briefings include information about:
- Weather phenomena
- Visibility
- Wind speeds and directions
- Temperature
- Cloud cover
- Precipitation
- Significant or hazardous conditions, such as thunderstorms, turbulence, and icing
- Aeronautical information, such as NOTAMs, military activities, flow control information, and TFRs

5.3 Decoding METARs

In this lesson, you will learn to decode hourly routine aviation weather reports known as METARs (said "MEE-TAR").

Decoding a Meteorological Aerodrome Report (METAR) is a way to understand the weather conditions for pilots:
What it is
A METAR is a standardized weather report for aviators that includes information such as temperature, wind, visibility, and cloud cover.
How to read it
A METAR report follows a pattern that includes the place, date and time, wind, visibility, phenomena, clouds, temperature, and pressure.
What it contains
A METAR may also include information on precipitation amounts, lightning, pilot reports, color states, and runway visual range.
What it doesn't contain
METARs don't report forecast weather, which is the purpose of a Terminal Aerodrome Forecast (TAF).
How to decode it
You can break a METAR into chunks, start with the ICAO designator, check the date and time, and look at the wind, cloud cover, temperature, and dew point information.
Where to learn more
You can learn how to decode a METAR on websites like Weather for Pilots.

5.4 Decoding TAFs

In this lesson, you will learn to decode hourly routine aviation 24-hour weather forecasts known as Terminal Area Forecast or TAF.

Aviation decoding TAFs, or Terminal Area Forecasts, involves interpreting the weather forecast for an airport and its surrounding area:
What is a TAF?
A TAF is a forecast of the weather conditions for a specific airport and its surrounding area for a set period of time. TAFs are issued every 6 hours and can be valid for up to 30 hours.
How to decode a TAF?
TAFs are written using a standard code format that includes weather codes, timespans, and probabilities:
- Weather codes: Use a variety of codes to describe weather conditions, such as BR for mist, DZ for drizzle, FG for fog, and RA for rain.
- Timespans: Written in the format DDTT/DDTT, where DDTT indicates the date and hour. For example, 0312/0409 indicates a timespan from 12Z on the 3rd to 09Z on the 4th.
- Probabilities: Written as PROB30 or PROB40, where 30 indicates unlikely and 40 indicates likely.
Other information
A TAF may also include the airport identifier code, the date and time of issue, the overall trend of the weather, wind strength and speed, visibility, cloud base, and precipitation.

5.5 Understanding Radar

Radar can provide valuable information. It is critical, however, that you understand it's limitations.
Radar systems work by transmitting radio waves into the air and then receiving the reflected waves. The time it takes for the radio wave to travel to an object and back to the receiving antenna determines the range. The position of the rotating antenna when the reflected wave is received determines the direction of the object.

Radar systems work by transmitting radio waves into the air and then receiving the reflected waves. The time it takes for the radio wave to travel to an object and back to the receiving antenna determines the range. The position of the rotating antenna when the reflected wave is received determines the direction of the object.

Radar, which stands for "radio detection and ranging", is a vital electronic system in aviation that uses radio waves to detect, locate, and monitor objects. Radar is used for many critical functions in aviation, including:
Navigation: Radar helps aircraft navigate.
Collision avoidance: Radar helps aircraft avoid collisions.
Air traffic management: Radar helps manage air traffic.
Height measurement: Radio altimeters measure the height of an aircraft above the surface.
Communication: Secondary surveillance radar allows aircraft to communicate with the interrogating radar.

5.6 Graphic Weather Products

It is important that you understand the symbology used on graphic weather products.
Aviation Graphic Weather Products are a set of tools that provide weather information for aviation, including forecasts, observations, and warnings.

Graphical Forecasts for Aviation (GFA)
A website that provides observational data, forecasts, and warnings for the United States, the Caribbean, the Gulf of Mexico, Alaska, Hawaii, and parts of the Atlantic and Pacific Oceans. GFA includes information on:
- Ceilings and visibilities
- Clouds
- Precipitation and weather
- Thunderstorms
- Winds
- Turbulence
- Ice

G-AIRMET (Graphical AIRMETs)
A graphical advisory of weather that may be hazardous to aircraft, but are less severe than SIGMETs

5.7 Weather Warnings

It is important that you know how to interpret in-flight weather warnings. This lesson covers the types you might encounter.

Aviation weather warnings are issued to alert pilots and others to potentially dangerous weather conditions that could impact a flight:
Turbulence: Air movements that can cause an aircraft to move rapidly and unexpectedly
Low-level wind shear: A rapid change in wind speed or direction, or both, that occurs near the ground
Sustained surface winds: Wind speed and direction at the runway can significantly impact take-offs and landings
Icing: Liquid water can exist even when the air temperature is below freezing
Freezing levels: The height at which the air temperature drops below 32°F (0°C)
Thunderstorms: Can disrupt the atmosphere with lightning, rain, hail, and strong winds
Volcanic ash: Ash clouds can be released to different heights and thicknesses after a volcanic eruption

5.8 Winds and Temperatures Aloft

Winds Aloft play a critical role in determining the distance we can fly. It's important to make sure you understand how to read that information.

Aviation winds and temperatures aloft, also known as an FD or FB, is a forecast of wind and temperature conditions at specific altitudes above the Earth's surface. It's a crucial component of flight planning and navigation, as it affects an aircraft's performance, fuel consumption, and flight path.

Here are some things to know about aviation winds and temperatures aloft:
How it's used
Pilots and flight dispatchers use winds and temperatures aloft to optimize flight paths and ensure safe and efficient travel.
What it predicts
Winds and temperatures aloft forecasts can predict the existence of head winds or cross winds, which can significantly change flight times and fuel consumption. Temperatures aloft can also show temperature inversions, which are unusually warm layers that can affect climbing performance.
How it's reported
Winds aloft reports typically cover various altitudes, commonly at 3,000 feet increments starting from 6,000 feet. They provide information on wind direction and speed. For example, "26016" means the wind is coming from 260 degrees at 16 knots.

5.9 Notices To Air Missions

NOTAMs are a systematic way of getting very important information to the pilot in command of a flight. It is critical you understand them and get them systematically.

A Notice to Air Missions (NOTAM) is a bulletin issued by an aviation authority to alert pilots of potential hazards or changes that could affect their flight:
Purpose
NOTAMs provide information that's essential for flight operations but not known far enough in advance to be publicized by other means.
Examples
NOTAMs can alert pilots to issues such as:
- A NAVAID that's out of service
- A Temporary Flight Restriction (TFR) that's active
- A runway, taxiway, or apron that's closed for maintenance
- A warning light at an airport radio tower that's failed

5.10 Decoding PIREPs

In this lesson you will learn to decode pilot weather reports, called PIREPs.

A PIREP, or Pilot Report, is a report of weather or other conditions encountered during a flight. Decoding a PIREP is important for pilots to understand and use to help them fly safely.

Here are some things to know about PIREPs:
What they contain
PIREPs include information about atmospheric conditions, like temperature, icing, and turbulence, as well as airport conditions, like runway conditions and ground equipment failures.
How they are created
Pilots create PIREPs and submit them to flight service or Air Traffic Control (ATC). They can also be submitted electronically through an electronic flight bag application or the Aviation Weather Center website.
How they are disseminated
PIREPs are usually transmitted by radio to the nearest ground station, but can also be made by telephone after landing.
How they are used
PIREPs are used as a supplement to general forecasts for an area and are often more accurate and precise. ATC uses PIREPs to gather and disseminate information about potential hazards to help pilots avoid them.
How they are identified
PIREPs include a UA or UUA to indicate if the PIREP is routine or urgent.

5.11 Using the Skew-T

The Skew-T chart (graphs which display temperature and dewpoint data vertically in the earth's atmosphere) can be a powerful tool to get information about where ice might be encountered.
Learning to use a Skew-T diagram can improve a pilot's flight experience. Hands-on courses can teach pilots how to use the diagram, including how to measure and chart the atmosphere, and the importance of parcel theory.

Pilots use Skew-T diagrams (also known as Skew-T Log-P thermodynamic diagrams) to help plan flights by analyzing the atmosphere and predicting weather conditions:
What it shows
Skew-T diagrams plot temperature and pressure, and include lines that represent other atmospheric conditions, such as dew point, wind speed and direction, and freezing levels
What it's used for
Pilots use Skew-T diagrams to predict icing levels, turbulence, convective weather, cloud tops, and precipitation
How it's used
Pilots can use Skew-T diagrams to evaluate and forecast the properties of air parcels. For example, negative values on a Skew-T diagram indicate an unstable atmosphere
How it's read
The Y-axis on a Skew-T diagram represents altitude, the X-axis represents temperature, and the lines represent temperature skewed northeast-southwest

Chapter 6: IFR Charts and Publications

6.1 Introduction to Charts & Publications

Content is essential and a challenge we will happily accept when presenting this IFR material. This is a quick introduction to the following chapter.

Aircraft charts and publications are maps and information used for air navigation, including:
Aeronautical charts, maps used for flight navigation that include information such as airports, airspace, navigation routes, hazards, and topographic features. The NAAs publishes aeronautical charts in print and electronically.

6.2 The Low Altitude Enroute Chart

The Low Altitude Enroute Chart is published every 56 days and covers the low altitude route structure of the National Airspace (from 1,000 feet up to but not including 11,000 feet).

An aircraft Low Altitude Enroute Chart is a navigation tool for pilots flying under instrument flight rules (IFR) below 18,000 feet MSL.

The charts include aeronautical information such as:
- Air Traffic Services
- Airports with an Instrument Approach Procedure or a minimum 3000' hard surface runway
Airways
- Limits of controlled airspace
- VHF radio aids to navigation
- Off Route Obstruction Clearance Altitudes (OROCA)
- Airway distances
- Reporting points
- Special use airspace areas
- Military Training Route

6.3 Instrument Departure Procedure (DP) Charts

Many airports have standard charted departure procedures (DPs) that are used to transition IFR traffic from the airport to the en route environment. This lesson covers the essential symbols and features of DP charts.

Instrument departure procedures are preplanned IFR procedures that provide obstruction clearance from the terminal area to the appropriate en route structure. Primarily, these procedures are designed to provide obstacle protection for departing aircraft.

6.4 Standard Instrument Arrival Route (STAR) Charts

Many airports have Standard Instrument Arrival Routes (STARs) that are used to transition IFR traffic from the en route environment to an instrument approach procedure. This lesson covers the essential symbols and features of STAR charts.

Standard Instrument Arrival Route (STAR) charts are aeronautical charts that provide flight crews with information on how to follow a STAR. STARs are flight routes that aircraft follow during an instrument flight rule (IFR) flight plan. They are published by the air navigation service provider and are used to guide aircraft from an intermediate altitude to the airport.

STAR charts help aircraft navigate terrain, airspaces, and departing traffic. They also help to: Simplify clearance delivery procedures, Transition between en route and instrument approach procedures, Ease congestion in the skies, Reduce radio chatter, and Speed up clearances.

To use a STAR, pilots can:
- Check the ATIS/D-ATIS for the runway(s) and preferred STAR(s) in use
- Load the STAR into their flight plan
- Follow ATC instructions, which take precedence over their flight plan

6.5 Introduction to Approach Charts

Instrument Approach Procedure (IAP) Charts are probably the most frequently used publication during IFR flying. Here We will provide an introduction to these charts and an overview of the two lessons covering approach charts in detail.

Aircraft approach charts, also known as Instrument Approach Procedures (IAPs) or approach plates, are charts that pilots use to guide them during instrument flight rules (IFR) flights. They help pilots land safely in conditions like fog, rain, snow, low ceilings, and reduced visibility.

IAPs provide pilots with: Specific waypoints, Targeted altitudes, and Procedures for approaches.
Each country has its own IAPs, which conform to ICAO standards.

The charts include information such as:
- The name and ICAO code of the airfield
- The type of chart
- The name and type of approach on the runway
- A frequency list of available air traffic controllers
- ILS parameters, such as localizer frequency, course, glide scope altitude, ILS decision altitude, and airport elevation altitude
- VOR parameters, such as VOR frequency

6.6 Instrument Approach Charts - Briefing and Minimums

Terminal Approach Procedures are published every 56 days containing all Instrument Approach Charts. These provide the information required to land safely in low visibility conditions. This lesson covers an introduction to IAPs and sections essential to an approach briefing.

When briefing an aircraft approach chart, pilots review the chart to identify minimums and other important information to help them navigate the approach and landing:
- Minimums: Verify the minimums category and set them in the avionics.
- Missed approach: Brief the missed approach point, including its distance, timing, or location relative to the runway.
- Terrain: Review terrain, man-made obstructions, and other hazards.
- Approach conditions: Consider weather and runway conditions.
- Instrument approach procedure: Review the details of the procedure, including the initial steps of the missed approach.
- Stabilization height: Review the stabilization height.
- Final approach descent gradient: Review the final approach descent gradient and vertical speed.
- Automation: Review the use of automation, such as lateral navigation (LNAV) and vertical navigation (VNAV).
- Communications: Review communications.
- Abnormal procedures: Review abnormal procedures, if applicable.
- Fuel status: Review the fuel status.
- Alternate airports: Review the status and availability of alternate airports in case of a missed approach.

6.7 Approach (IAP) Charts - Plan and Profile Views

This lesson looks at the two sections of Instrument Approach Procedure (IAP) charts that provide essential lateral and vertical navigation information for the approach procedure: The Plan view and the Profile view.

An Instrument Approach Procedure (IAP) chart has two views that help pilots navigate to an airport: the plan view and the profile view:
Plan view
Provides a "bird's eye" view of the approach, including the approach course, intersections, terrain data, and missed approach information. Pilots use this view to ensure they are in the correct position along the approach path.
Profile view
Provides a side view of the approach, including the approach course, minimum altitudes, step-down fixes, final approach fix, and missed approach information. This view is essential for flying an instrument approach safely because it provides the only safe altitudes for each segment of the approach.

6.8 The Chart Supplement

The Chart Supplement is published every 56 days and was formerly called the Airport / Facility Directory, or AFD. This explains essential information.

The Aircraft Chart Supplement, formerly known as the Airport/Facility Directory (AFD), is a series of publications issued by the NAAs that provides information on airports, seaplane bases, heliports, and other aviation facilities:
What it contains
Information on airport services, frequencies, runway lengths, navigational facilities, airport diagrams, communications data, and more
How it's used
Designed to be used in conjunction with charts, the Chart Supplement provides more information than can fit on the sectional chart
How often it's published
The NAAs issues the Chart Supplements as & when required
What's included
The Chart Supplement includes information on all open-to-the-public airports, seaplane bases, heliports, military facilities, and some private-use airports

6.9 The Chart Supplement - IFR Specifics

This lesson covers contents of the Chart Supplement that are specific to IFR flying. The Chart Supplement is a useful source of information, but pilots should be able to decipher complex charts, codes, and acronyms.

An aviation Chart Supplement is a publication that provides information about airports and is designed to be used with IFR or VFR charts:
What it includes: Data on airports, NAVAIDs, communications, weather, airspace, special notices, and operational procedures
What it's used for: Finding airports that can provide the right maintenance, fuel, or oxygen refill
How it's used: In conjunction with Sectional Charts, High Enroute Charts, Low Enroute Charts, or other visual charts
How often it's published: Every 56 days
What's included in the Runway Data section: Runway dimensions, material, weight bearing capacity, pavement classification number (PCN), and lighting
How to decipher it: Use the legend to understand the numbers, symbols, and colors on the chart

Chapter 7: Radio Navigation

7.1 Reviewing VORs

This lesson covers the basic concepts of the Very High Omni Range that are a pre-requisite to instrument training. You covered this material during Private training but it's important to review.

VOR is a type of navigation aid (navaid) that uses very high frequency radio signals emitted by radio beacons. VOR stations broadcast three letter identifiers in Morse code. Because VOR signals have a range of about 200 miles, it is possible for an aircraft to receive multiple VOR signals. Therefore, it is necessary that pilots identify the correct VOR before navigating to it.

7.2 VOR Minimum Operational Network

For aircraft that do not carry GPS or DME, national authorities are retaining a limited network of VORs, called the VOR Minimum Operational Network, to provide a basic conventional navigation service for operators to use if GNSS becomes unavailable.

7.3 VOR for IFR Operations

The VOR still serves an essential role in the low-altitude national airspace system.

VOR, or very high frequency omni-directional range, is a radio navigation system that helps pilots determine their position and maintain their course during Instrument Flight Rules (IFR) operations:
How it works
VORs are ground-based transmitters that broadcast two signals: a constant omnidirectional signal and a directional signal that rotates 360°. The VOR receiver in the aircraft measures the phase shift between the two signals to determine the aircraft's bearing relative to the VOR.
VOR uses
VORs are used for en-route navigation, approach procedures, and to define Class B airspace sectors.
VOR checks
Before flying IFR using VOR, pilots must perform a VOR check within the previous 30 days. The check involves tuning the aircraft's NAV-1 and NAV-2 to the same VOR frequency, choosing the same radial on both instruments, and comparing the needle accuracy of each instrument. The pilot must record the date, place, bearing error, and sign the aircraft log.

7.4 NDB for IFR Operations

NDBs are still widely used in some countries, and are an important part of the instrument pilot's toolkit.

A non-directional beacon (NDB) is a radio transmitter that emits a signal in all directions, which aircraft use to navigate:
How it works
The NDB's signal is received by the aircraft's automatic direction finder (ADF), which determines the direction of the signal. The pilot then follows the ADF's direction to fly over the NDB.
Where it's used
NDBs are used for instrument approaches at airports and offshore platforms. They're also associated with non-precision approach procedures.
Advantages
NDBs are reliable, inexpensive to install and operate, and can provide decades of service. They can also be received at greater distances at lower altitudes because their signals follow the curvature of the Earth.
Disadvantages
NDB signals can be affected by atmospheric conditions, mountainous terrain, coastal refraction, and electrical storms. At night, distant stations can interfere with NDBs.

7.5 Understanding GPS

Global Positioning System is a revolutionary satellite-based navigation system that has transformed the way pilots navigate in the sky. By the end of this lesson, you'll have a solid understanding of GPS.

The Global Positioning System (GPS) is a satellite-based radio-navigation system that provides accurate information on position, velocity, and time. It's used by aviators to increase the safety and efficiency of flight.

GPS receivers use an atomic clock to measure the signal, and the time it takes for the signal to get there determines where you are in time and space.

Here are some ways GPS is used in aviation:
Navigation: GPS provides continuous, reliable, and accurate positioning information for all phases of flight, including departure, en route, arrival, and airport surface navigation.
Route selection: GPS can help aviators find safe, flexible, and fuel-efficient routes.
Aircraft delays: GPS can help reduce aircraft delays.
Safety: GPS can increase safety-of-life capabilities.

7.6 GPS for IFR Operations

GPS is the most prevalent technology in today's cockpit and provides a very accurate indication of aircraft position and speed. Dive deeper than "direct to" and understand how to operate beyond following the magenta line.

Aviation GPS for instrument flight rules (IFR) operations is a technology that uses radio waves to help guide aircraft in low-visibility conditions and navigate to and from airports and navaids:

How it works
GPS receivers use data from satellites to calculate their position and distance from a source. The math involved is complex and uses Einstein's Theory of Relativity.
Requirements
To use GPS for IFR operations, the GPS must meet the following requirements:
- Be permanently installed in the aircraft
- Be certified as a TSO C129 (non-WAAS) or TSO C145/146 (WAAS) receiver
- Have a current database
- Use receiver autonomous integrity monitoring (RAIM)
What it can do
GPS can be used for instrument approaches (IAPs) and can provide information such as heading, airspeed, altitude, and course information.

7.7 Wide Area Augmentation System (WAAS) Overview

The Wide Area Augmentation System (WAAS) is a navigation system comprising satellites and ground stations that improve the accuracy of the Global Positioning System (GPS).

The Wide Area Augmentation System (WAAS) provides extremely accurate navigation capability by augmenting the Global Positioning System (GPS). It was developed for civil aviation by the Federal Aviation Administration (FAA) and covers most of the U.S. National Airspace System (NAS) as well as parts of Canada and Mexico.

Chapter 8: Approaches, Arcs, and Holds

8.1 Precision Approaches

Precision Approaches are the most precise approach and will allow you to land in the lowest possible weather conditions. They always have vertical guidance and end with an approach lighting system and a runway with precision markings.

A precision approach is a standard instrument approach procedure that uses electronic guidance to guide an aircraft down to a runway:
Guidance
Precision approaches provide both vertical and lateral guidance, either from a ground-based navigation aid, computer-generated data, or a controller.
Equipment
Precision approaches use a variety of equipment, including:
- Instrument Landing System (ILS): Uses VHF signals to provide course information, and is the most common for airliners
- Precision Approach Radar (PAR): Used to detect and display aircraft, determine aircraft position, and provide guidance instructions to the pilot
- GBAS Landing System (GLS): Uses GPS satellite systems and ground transmitters, and is an alternative to ILS for difficult approaches

8.2 Instrument Landing System (ILS)

The ILS is one of the most common approaches utilized for IFR operations. This lesson takes a deeper dive into how ILS approaches are flown and some of the errors associated with them.

The ILS is a standard precision landing aid used by the International Civil Aviation Organisation (ICAO).

An Instrument Landing System (ILS) is a radio signal navigation aid that helps pilots land an aircraft on a runway in low visibility or adverse weather conditions. The ILS sends information to the cockpit instruments to help the pilot maintain a predetermined flight path.

The ILS has two subsystems that provide guidance to the aircraft:
Localizer
Provides lateral guidance to keep the aircraft from shifting from the recommended path. The localizer antenna is located at the southern end of the runway.
Glide slope
Provides vertical guidance to keep the aircraft from deviating vertically from the recommended path. The glide path tower is located next to the runway at the northern end.

8.3 Nonprecision Approaches

Nonprecision approaches are, by definition, usually less precise. Traditional nonprecision approaches have no vertical guidance. However, GPS technology is changing all of that to some extent.

Non-precision approaches are also known as non-ILS approaches. They can be flown using a variety of navigational aids, including: Distance Measuring Equipment (DME), Precision Approach Path Indicators (PAPI), and Visual Approach Slope Indicators (VASI).

Pilots must calculate and maintain their own glide-slope path, and conform to the minimum altitude requirements of the approach. The descent path can vary considerably, which can lead to accidents.

A non-precision approach is a type of instrument approach and landing that uses lateral guidance to navigate an aircraft to the runway, but does not provide vertical guidance:
Lateral guidance
Provided by navigation aids like VHF Omnidirectional Range (VOR), Non-Directional Beacon (NDB), or GPS waypoints
Vertical guidance
Based on the pilot's situational awareness and other navigational aids, such as timing based on radio beacons or a table from an aviation chart
Accuracy
Non-precision approaches are less accurate than precision approaches, so they require good weather conditions and are often used as a backup

8.4 VOR Approaches

The VOR approach is perhaps one of the easiest approaches to fly and requires minimal extra equipment. This lesson dives into the basics of flying a VOR approach and provides an example of how it can be used.

A VOR approach is a non-precision approach that uses a VHF Omni-Directional Range (VOR) radio to help guide an aircraft laterally.
How it works
A VOR sends out two signals, a stationary reference phase and a rotating variable phase. The aircraft's VOR antenna picks up the signals and sends them to the cockpit receiver. The receiver compares the two phases to determine the aircraft's bearing.
Steps for a VOR approach
Pilots typically brief the approach, set up the aircraft parameters, prepare the course, and take the VOR frequency from charts. The pilot-in-command is responsible for the descent.
VOR-A approach
A VOR-A approach is a circling approach, which means the final approach course is more than 30 degrees from the extended centerline at the missed approach point. A VOR-A approach may be the only option if the GPS is not working.

VORs operate in the 108.0 MHz–117.95 MHz band and can help aircraft determine their azimuth, or compass heading, relative to a VOR.

8.5 Localizer Approaches

LOC approaches are the bread-and-butter for an airfield in mountainous terrain—one without the required climb gradient for an ILS or when the glide slope is inop. We'll review how to set up and execute a LOC-only approach to touchdown safely.

A localizer (LOC) approach is a non-precision runway approach that uses a radio beam to help pilots align their aircraft with the runway's centerline during landing.

Here are some key features of a localizer approach:
Radio signals
The localizer transmits radio signals in the VHF (Very High Frequency) band, typically between 108.10 and 111.95 MHz.
Antennae
The localizer's antennae are usually located at the end of the runway.
Signal corridor
The localizer's radio signals create a signal corridor called the "localizer course".
Navigation receivers
Aircraft have onboard navigation receivers that pick up the localizer's signal and track the localizer course.
Course deviation information
Cockpit instruments display course deviation information to help pilots stay on course.
Accuracy
Localizer systems are designed to provide accurate lateral guidance, especially in low visibility or adverse weather.

LOC approaches can be used as stand-alone approaches or as a downgrade option for an Instrument Landing System (ILS).

8.6 RNAV / GPS Approaches

Although flown similarly to a precision or non-precision approach, RNAV (GPS) Approaches are their own category; APV. This lesson dives into GPS approaches and some of the nuances associated with them.

RNAV (Area Navigation) / GPS approaches are a method of navigation that allows aircraft to fly between points using ground- or space-based navigation aids, or a combination of both:
RNAV
Allows aircraft to fly to any point within the coverage zone of a station, bypass published routes, and fly instrument approaches to airports without ground-based navigation stations.
GPS
Satellite Navigation is the go-to source for RNAV navigation because it's available and accurate almost all the time.
RNAV (GPS) approaches
There are several types of RNAV (GPS) approaches, including:
- LNAV (Lateral Navigation): A nonprecision approach that uses GPS and/or WAAS.
- LP (Localizer Performance): A nonprecision WAAS-mandatory approach.
- APV (Approach with Vertical Guidance): An instrument approach that provides course and glidepath deviation information.

8.7 Circling Approaches

Circling approaches are approaches that are not directly aligned with any runway and require maneuvering upon the completion of the approach.

A circling approach is a visual flight maneuver that allows a pilot to land an aircraft at an airport when a direct landing is not possible. It's often used when:
- The runway is not aligned with the initial instrument approach
- Wind conditions or obstacles make a direct landing impossible
- The ILS approach is aligned to a different runway than the one the pilot wants to land on
- Landing on the instrument runway is undesirable

Circling approaches are considered one of the most challenging flight maneuvers and can be risky. They require the pilot to:
- Maneuver the aircraft manually for landing
- Maintain visual contact with the runway
- Exercise careful judgment and skill, especially in poor weather conditions

8.8 Missed Approaches

Missed approaches are approaches that cannot be completed. The missed approach procedure guides the pilot safely back to altitude.

A missed approach is a well-practiced maneuver that's not usually an emergency, but it can be stressful. To perform a missed approach safely, a pilot needs: Good instrument flying skills, The right mindset, and A methodical and decisive approach.

A missed approach, also known as a go-around or aborted landing, is a standard maneuver where a pilot stops an aircraft's approach to the runway and climbs back into the air to circle around for another attempt.

A pilot might initiate a missed approach if:
- Can't see the runway or its surroundings
- Can't safely land for any reason
- Encounter adverse weather conditions, such as strong winds
- See debris on the runway
- Another aircraft is on the runway or hasn't cleared it yet

8.9 Visual Approaches

A visual approach is an IFR approach that relies on visual contact with the runway or the preceding airplane that has visual contact with the runway.

A visual approach is when a pilot flies an aircraft to an airport while visually referencing the terrain and clear of clouds. It's an approach that's authorized by air traffic control (ATC) and is usually the first type of approach taught to student pilots.

Here are some things to know about visual approaches:
Benefits
Visual approaches can reduce workload for flight crews and maximize traffic flow for controllers.
Risks
Visual approaches can be hazardous and may result in unexpected occurrences like landing at the wrong airport or without clearance.
Procedure
The pilot must be able to see the airport or the preceding aircraft at all times. The pilot is usually positioned by a radar controller and asked to "report the airfield in sight" before being cleared for the approach.
Go-around
If an aircraft can't complete a landing, it must be handled like a go-around.
Airport lighting
Turning on airport lighting can help pilots reference the VASI or PAPI as they descend to the runway.

8.10 Holding Patterns

Holding patterns are used to kill time in the air. The need to kill time in the air can occur for various reasons but the holding procedures remain the same.

An aviation holding pattern is a racetrack-shaped course that an aircraft flies while waiting for air traffic control (ATC) clearance:
Purpose
Holding patterns are used to delay an aircraft's descent toward the runway. They can also be used to:
- Manage the flow of air traffic in busy airspace
- Allow pilots to delay their approach until weather conditions improve
- Coordinate further clearance after a missed approach
- Allow time for pilots to complete abnormal or emergency checklist procedures
When they happen
Holding patterns can happen for a number of reasons, including:
- Congestion
- Bad weather, such as reduced visibility, strong winds, or snow
- Equipment malfunction
- Obstructed runway
How they work
Pilots don't have to fly manually because their guidance systems help the aircraft maintain its holding pattern. The point around which the aircraft holds around is called a "holding fix".
Parts of a holding pattern
A holding pattern is made up of multiple parts, including:
- Holding fix
- Inbound leg
- Outbound leg
- Protected airspace

8.11 Procedure Turn Course Reversals

Course reversals are integral to flying in non-radar environments. We'll learn the different types of turns and dive into the intricacies of flying full approach procedures, delaying commencing an approach, or aligning the aircraft towards the runway.

A procedure turn (PT) is a course reversal maneuver that helps an aircraft line up with the final approach course for an instrument approach. It's a required maneuver when it's shown on the approach chart.

A procedure turn typically involves:
- Turning off the outbound course by 45 degrees
- Flying for one minute
- Turning back to the inbound approach course by 180 degrees

To help with the procedure turn, you can:
- Power back on the throttle so you don't go too fast around the turn
- Note the time on your clock so you know how long to fly

Other types of course reversals include:
- Teardrop patterns: Allow the pilot to lose altitude while making one turn
- DME arcs: May require constant turning and monitoring
- Holding patterns: Another type of course reversal

8.12 DME Arcs

Knowing how to fly an arc to a final approach course is a critical maneuver to master. This is used in lieu of flying a full procedure and just another way for ATC to sequence aircraft.

A DME arc is a curved route that pilots fly at a constant distance from a navigation aid (NAVAID) like a VOR, VORTAC, or NDB/DME. DME stands for Distance Measuring Equipment, which is used to measure the distance between an aircraft and a facility.

DME arcs are typically used in the initial approach segment to guide aircraft from the Initial Approach Fix (IAF) to the Final Approach Course. The arc's radius is usually between 7–30 nautical miles (NM), and its length is usually between 5–15 NM, with 10 NM being the preferred length.

Here are some things to know about DME arcs:
Flying a DME arc
Pilots on less sophisticated aircraft need to constantly change their heading and monitor the VOR radials to stay within the arc. On more sophisticated aircraft, these heading changes are made automatically.
Using radar vectors
In real-world operations, pilots use DME arcs in combination with radar vectors from Air Traffic Controllers.
Anticipation
Pilots need to anticipate a 90° interception turn when entering and leaving the DME arc.
Wind correction angles
Pilots need to adjust for wind correction angles as the aircraft moves through the arc.
End point
Each arc has a charted end point where the aircraft intercepts an intermediate segment. Pilots can set a heading bug on the inbound course to help them find this target.

8.13 Contact Approaches

A contact approach allows a pilot in visual contact with the ground to follow known terrain features to the airport. Contact approaches can only be flown into airports that already have an instrument approach procedure available.

A contact approach is a flight procedure that allows pilots to use visual references to the ground to land at an airport instead of following a published instrument approach procedure. It's similar to a visual approach, but with less stringent visibility requirements and without the need to see the airport or other aircraft at all times.

Contact approaches are used in situations such as:
- When airports don't have published approach procedures
- When there are local weather issues, like a fog bank
- When you're vectored for an instrument approach but can see the airport through breaks in the clouds

Here are some tips for performing a contact approach:
- Ensure the weather conditions and visibility are suitable
- Request clearance from Air Traffic Control (ATC)
- Keep visual contact with the ground and landmarks
- Use navigation aids to verify your position and heading
- Confirm that you've received ATC clearance and understand all instructions

Be aware of obstacles around you, as you're responsible for traffic and terrain avoidance.
Contact approaches can be useful at both controlled and uncontrolled airports, but it's not recommended to try one at an unfamiliar airport.

Chapter 9: ATC and IFR Clearances

9.1 Filing IFR Flight Plans

In order to fly IFR, you need to file a flight plan and receive a clearance. There are a couple different ways to do this, which we'll discuss in this lesson.

IFR stands for Instrument Flight Rules, which are a set of regulations that require pilots to use instrument navigation instead of visual references. IFR flights are more complex and require advanced skills, such as a thorough understanding of the aircraft's instruments and equipment.

An IFR flight plan is a document that pilots must file before taking off in conditions where they can't rely on visual cues:
When to file: At least 30 minutes before the estimated departure time
What's included: Waypoints, altitudes, and air traffic control (ATC) clearances
Who files: Pilots who are IFR rated and can fly the aircraft using only the instruments
How to file: Call or contact the local flight service station (FSS) with the pilot's name, phone number, true airspeed, route, and fuel on board
Purpose: Used by air traffic control to initiate tracking and routing services

9.2 IFR Clearances

IFR is one of two sets of regulations that govern all aspects of civil aviation aircraft operations. The other set is visual flight rules (VFR). The IFR clearance is the backbone of any IFR flight. It is your route from departure to destination and your backup plan in a lost communication situation.

An Instrument Flight Rules (IFR) clearance is a document that allows a pilot to fly through controlled airspace under specific guidelines. Air Traffic Control (ATC) issues IFR clearances at both controlled and uncontrolled airports.

To get an IFR clearance, pilots must:
1. Contact ATC by radio before taxiing
2. Provide essential information, such as:
- Aircraft call sign
- Type and equipment suffix
- Departure and destination airports
- Proposed departure time
- Final altitude and route information

Pilots can also request a "pop-up IFR" clearance while flying under visual flight rules (VFR) if weather conditions deteriorate or they need help navigating.
IFR clearances include the following information: Aircraft identification, Clearance limit, Cleared level(s), and Allocated SSR code (squawk/transponder code).

Clearances follow a format that can be remembered by the acronym CRAFT, which stands for: Clearance limit, Route, Altitude, departure Frequency, and Transponder code.

Pilots should read back or acknowledge clearances to indicate that they understand and will comply with them.

9.3 Cruise Clearance

An IFR cruise clearance allows a pilot to choose the altitude at which they'd like to operate within the bounds of the ATC clearance. Pilots are still required to fly an IFR route.

In aviation, a cruise clearance is an Air Traffic Control (ATC) authorization that allows a pilot to fly at any altitude within a specified range, and to approach and land at the destination airport:
Altitude range
The clearance specifies a block of airspace from the minimum IFR altitude up to and including the cruising altitude.
Approach
The clearance automatically includes permission to perform an instrument approach at the destination airport.
Descent
The pilot is responsible for planning the descent from the en-route altitude. They can use their knowledge of minimum instrument altitudes to determine how low to go.
Climb
The pilot can climb back to the cruising altitude at any time, unless they verbally report leaving that altitude.

A cruise clearance is based on known traffic and airport conditions. It's intended to prevent collisions between known aircraft.

9.4 VFR-On-Top

VFR-On-Top is an IFR clearance that allows a pilot to fly an IFR route while choosing VFR altitudes. Pilots are free to fly at whatever VFR altitude they'd like on top of the cloud layer.

VFR-on-top is a flight status that allows a pilot to fly above a cloud layer at VFR altitudes while maintaining IFR flight status. This clearance is mostly used in the United States and is granted by Air Traffic Control (ATC) after a pilot requests it.

Here are some things to know about VFR-on-top:
Benefits
VFR-on-top allows pilots to navigate above large cloud layers or in varying weather conditions. It can also help pilots avoid air sickness by allowing them to see distant objects.
Requirements
Pilots must comply with VFR visibility and distance-from-cloud criteria, as well as IFR regulations applicable to their flight. They must also be vigilant to see and avoid other aircraft.
- It’s ONLY for pilots operating under an IFR flight plan.
- Must maintain VFR cloud clearances the ENTIRE time.
Requesting clearance
Pilots can request VFR-on-top clearance on the ground, usually from clearance or ground control at a towered airport. They should specify the route they want to take, the altitude they want to reach, and their aircraft type.
Rules vary by country
The rules for flying VFR-on-top vary from country to country. For example, the Canadian VFR-on-top regulations are more restrictive than the US Federal Aviation Regulations.

Chapter 10: Aeromedical and ADM

10.1 Aeronautical Decision Making

In this lesson you will learn about one of the hardest and most important parts of good airmanship, aeronautical decision making, ADM.

Aeronautical Decision Making (ADM) is the process pilots use to evaluate a situation and decide on the best course of action in an aviation environment. ADM is a systematic approach that pilots use to make decisions in all phases of flight, including before takeoff and during the flight.

The FAA Aviation Safety Program developed a framework for ADM called 'Perceive-Process-Perform' to help pilots put ADM into practice:
Perceive: Identify the circumstances of the flight
Process: Evaluate how these circumstances affect flight safety
Perform: Implement the best course of action

10.2 Spatial Disorientation

As the pilot you must do everything you can to predict and prevent spatial disorientation from occurring. That starts with you knowing a bit about how it works.

Aviation spatial disorientation is when a pilot is unable to accurately interpret their aircraft's position, motion, or altitude in relation to the Earth. It's a leading cause of aviation accidents and can lead to loss of control and a crash.

Some causes of spatial disorientation include:
Lack of visual references
Conditions like clouds, fog, haze, or darkness can make it difficult for pilots to maintain orientation.
Flight situations
Rapid rolls, banks and turns, graveyard spins, and pitching down too quickly can all cause spatial disorientation.
Malfunctioning instruments
A breakdown in the flight instruments can lead to spatial disorientation.
Sensory conflicts
The human body is designed for a two-dimensional environment, while aviation takes place in three dimensions. This can lead to sensory conflicts that make it difficult to maintain orientation.

Symptoms of spatial disorientation include:
- Dizziness or lightheadedness
- Unsteadiness or loss of balance
- Vertigo
- Confusion or disorientation
- Difficulty with visual and spatial abilities
- Difficulty with problem-solving or reasoning
- Nausea or vomiting

Pilots can compensate for spatial disorientation by learning to fly using their instruments.

10.3 PAVE, 5P, and DECIDE

The DECIDE and PAVE acronyms are designed to help you during stressful situations by giving you a specific device to help you process the information.

PAVE, 5P, and DECIDE are all decision-making models used by pilots to help them make effective decisions during flight:
PAVE
A checklist that pilots use to categorize risks before each flight. The acronym stands for:
P: Pilot: Ensure the pilot has the required documents, is physically and mentally fit, and is current
A: Aircraft: Ensure the aircraft has the required and current documents and equipment on board
V: Environment: Ensure the pilot is aware of the weather
E: External pressures: Ensure the pilot recognizes the factors that may add risk to the flight

5P
A practical way for pilots to evaluate their current situation at key decision points during the flight. The acronym stands for:
Plan: Consider airport conditions, terrain, airspace, and weather
Plane: Consider airworthiness, performance, and proper configuration
Pilot: Consider training, experience, and fitness
Passengers: Consider experience, flexibility, and fitness
Programming: Consider avionics airworthiness, operation, and configuration

DECIDE
A decision-making model that stands for:
Detect
Estimate
Choose
Identify
Do
Evaluate

Pilots use these models to help them define the problem, choose a course of action, implement the decision, and evaluate the outcome.

10.4 Automation Management

As more technology becomes available to pilots in the cockpit, it is extremely important that you learn to remain the Pilot In Command and manage the automation effectively.

Aviation automation management is the use of technology to perform tasks in the aviation industry with minimal human involvement.

Automation can include:
- Flight automation: Uses systems like autopilots and navigation aids to reduce the need for human interference
- Air traffic management: Uses automation to exchange data like flight plans and NOTAMs
- Aircraft maintenance: Uses automation for predictive maintenance, condition monitoring, and automated diagnostics
- Automation in the Aviation Industry

Automation can improve safety, efficiency, and accuracy in aviation. It can also reduce human error, increase flight system reliability, and improve fuel efficiency. However, as automation becomes more sophisticated, there are concerns about the potential for complacency among pilots.

10.5 Sinuses and Inner Ear

It's important to understand how the sinuses and inner ear work as you fly through various altitudes and flight conditions.

Sinuses and the inner ear can be affected by changes in air pressure during air travel, such as when an airplane climbs or descends:
Airplane ear
Also known as ear barotrauma, this is a temporary condition that can occur when there's a sudden change in air pressure. Symptoms include a feeling of fullness or blockage in the ear, pain, dizziness, and hearing loss. It's more likely to occur if you have congestion from allergies or a cold, as this can make it harder for your Eustachian tubes to manage air pressure changes.
Sinus discomfort
When an airplane climbs, the air pressure decreases, which can cause air to escape from the sinuses through the Eustachian tube and sinus openings in the nose. This can lead to sinus discomfort.
Toothache
Maxillary sinus discomfort can sometimes be mistaken for a toothache. If you experience a toothache while flying, you should see a dentist immediately.

To help with sinus pressure and ear block, you can try taking a non-drowsy decongestant or using a vasoconstrictor spray. Before taking a decongestant, make sure it's legal for you to take while flying, and that it's non-drowsy and approved by a doctor.

10.6 Hypoxia

Hypoxia is a lack of oxygen in the brain. Most hypoxia is due to reduced partial pressures at altitude but there is more to the story than that. It's important that you understand.

Aviation hypoxia, also known as altitude hypoxia, is a serious disorder that occurs when there is not enough oxygen in the air for the lungs to transfer to the blood:
Causes
At higher altitudes, the air pressure decreases, which means there is less oxygen available.
Symptoms
Confusion, restlessness, difficulty breathing, headache, rapid heart rate, bluish skin, lightheadedness, dizziness, tingling, sweating, impaired judgment, tunnel vision, and euphoria.
Risks
Hypoxia can occur quickly, and the body's ability to adapt is poor when it starts fast. Symptoms can vary from person to person and it can be hard to recognize.
Prevention
Flight crews should be well-informed about hypoxia and know how to protect themselves. The FAA requires supplemental oxygen for flights that exceed 30 minutes above 12,500 feet.

Hypoxia can occur in unpressurized aircraft flying above 10,000 feet, or in the case of oxygen system failure.

10.7 Hyperventilation and Dehydration

In this lesson we go over the symptoms of hyperventilation and dehydration both the traditional solutions and the practical realities of these two potential problems.

Hyperventilation is rapid breathing that can occur in aviation and can lead to dehydration:
Hyperventilation
When breathing too fast, you can remove too much carbon dioxide from your body, which can lead to a condition called alkalosis. Symptoms include dizziness, tingling, nausea, and muscle spasms. To correct hyperventilation, you can slow your breathing and breathe into a paper bag.
Dehydration
When flying, you can lose water through your skin and lungs due to dry air and low oxygen pressure. To prevent dehydration, you can drink 2–4 quarts of water per day, limit caffeine and alcohol, and acclimate to weather changes.

In aviation, pilots should be aware of hyperventilation and hypoxia, which can have similar effects and can occur together. To distinguish between the two, pilots can:
- Reduce breathing rate to normal and breathe 100% oxygen
- Descend to a lower altitude
- Inspect the oxygen system to check for malfunctions

Pilots can also train to recognize the signs and symptoms of hyperventilation and hypoxia in an altitude chamber.