How Do Airline Pilots Navigate In The Sky?

Want to become a writer at Eat My News? Here is an opportunity to join the Board of Young Leaders Program by Eat My News. Click here to know more:​ bit.ly/boardofyoungleaders

Every one of us might have at some point heard an airliner fly above us and have wondered how those pilots up there find their way flying so high in the sky. There are several methods and instruments that airline pilots use to navigate in the air. Finding their way in the sky comes under a very broad topic called Air Navigation. Out of the many different ways in navigation, this article looks at some of the methods used by airline pilots to navigate their commercial jets seamlessly over thousands of miles.

Modern airline jets are equipped with highly sophisticated instruments that assist the pilots to determine their position at all times and lets them know which way to fly. It's interesting to note that, they usually have two or more sets of all the vital instruments to guarantee safe flight in case one of the systems fails.

Navigation Systems

Depending on the phase of flight and availability of ground-based navigation facilities at different airports, airline pilots use the following instruments or a combination of these to fly from point A to point B. These systems include-

Inertial Reference System (IRS)

Global Positioning System (GPS)

Radio Aids (VOR, DME, NDB, ILS)

Onboard every modern airliner, there is a Flight Management System or Computer (FMS or FMC) which continuously monitors all the relevant information it receives from the various instruments in flight, including the navigation instruments mentioned above.

It's a two-way communication system between the pilot and the airplane which enables the pilot to get information and assistance and at the same he can instruct the aircraft to do stuff that he wants it to do.  This system enables the pilot to enter pre-planned routes and other data that is required to operate a particular flight.

Inertial Reference System (IRS)

When you switch on a commercial airliner, it’s like a baby that wakes up from its sleep and it doesn’t know where on earth it is. So the pilot will have to tell it where it is parked at the moment. He does this by feeding in its present position in coordinates - latitude and longitude, into the FMS/ FMC. The IRS (older versions are called INS-Inertial navigation system) is a complex instrument which includes several gyroscopes and accelerometers. 

Once the IRS gets its initial position as entered by the pilot it can continuously calculate its position as the aircraft starts moving and it relays this position to the pilot in the flight deck. The IRS does this by measuring the distance traveled by the aircraft in any particular direction and updating the present position as the aircraft moves.

The IRS is a system that works without any external reference other than the position at the start of the flight. It measures the aircraft's acceleration in all three axes and integrates this acceleration to get its velocity and the distance traveled. It's not as accurate as the GPS, because its position errors increase with time. But it is still sufficient enough to navigate an airplane with reasonable accuracy in case all other navigation reference is lost.

Global Positioning System (GPS)

The GPS is a satellite-based navigation system, which makes use of a constellation of 24 satellites that orbit the earth. It is owned by the United States of America and is available for civilian use since 1980.  The GPS receivers in commercial airliners receive position information from these satellites, just like you receive position information on your smartphone while using Google maps.

GPS can be used for primary navigation only in certain flight phases because of some of its limitations like poor satellite reception at times causing reliability issues. Specific certification and approval for both the airline and the aircraft are required to use GPS for primary navigation during departure, arrival, and approach phases of a flight. If the aircraft receiver fails or the satellites go out of range, the aircraft still has suitable redundancy to ensure safe navigation using other onboard equipment.

Even though GPS is the most widely used satellite navigation system, there are many similar systems owned by countries other than the USA. The Global Navigation Satellite System (GLONASS) is the Russian equivalent of the GPS. The Indian system, GAGAN— GPS Aided GEO Augmented Navigation is a regional satellite-based augmentation system that improves the accuracy of satellite receivers on aircraft by providing it with reference signals.

Radio Aids

Radio beacons such as the Very high-frequency Omni directional Radio range (VOR), Distance Measuring Equipment (DME), Non-Directional Beacon (NDB), and Instrument Landing System (ILS) are ground-based systems that the pilots use for navigation. An NDB is a beacon located on land or at the airport which transmits radio signals on a particular frequency. 

The receiver in the aircraft when tuned to the frequency identifies this signal and points towards the beacon emitting the signal. So you know where the signal is coming from and the relative direction of the airport from your location in the air.

The VOR is a short-range navigation system that is more widely used than the NDB as it gives you more information when compared to the NDB. VOR is also a radio beacon on the ground transmitting very high-frequency radio signals and it is more reliable than the NDB. VOR can be used along with a DME to get an accurate position and distance from a particular airport or ground station.

ILS or instrument landing system assists the pilots in the landing phase of flight by providing vertical and horizontal guidance. The radio beams emitted by the ILS antenna located near the runway define a slanted glide path in the air which can be followed by the pilots during the approach phase to fly down their airplanes to the runway.

Why Pilots Don’t Get Lost?

As you can see, modern commercial airliners are equipped with a wide range of instruments that assist the pilots to accurately navigate and find their way in the skies. They make use of self-contained systems like IRS and INS, satellite-based systems like GPS, GLONASS, and GAGAN, and ground-based systems like VOR, NDB, DME and ILS to name a few.

Flight Management System/ Computer constantly receives and monitors information from all these sources. This information is made available to the pilots as well, on their cockpit screens. The route that the pilots intend to fly is fed into the system and it is displayed on a moving map on the cockpit screen which the pilots monitor throughout the flight.

Apart from the route, the pilot can view other things around his flight path on the screens, such as the weather ahead of him, other airplanes flying around him, nearby airports, and the terrain beneath the airplane. Each of these information is provided by its dedicated sources and instruments and it is beyond the scope of this article. Along with all these instruments, there are dedicated maps and charts that are used by pilots to fly any designated route and navigate to an airfield.

State regulations require airliners to be equipped with more than one set of these instruments and several other types of equipment to ensure safety in case one of these fails. For example, a Boeing737NG aircraft has two IRS, two GPS receivers, and usually two sets of VOR and ILS. Just like most of the aircraft systems, there is a lot of redundancy on board when it comes to navigation equipments. That's why pilots don't get lost very often! 


Written by - Rahul Prem

Edited by - Nidhi Verma