Part 5: How do Aircraft Navigate?


In the last edition, we spoke about the problem with many existing noise abatement procedures that they are not integrated into flight procedures that govern how aircraft will arrive to and depart from an airport. In this installment, we will outline how aircraft navigate along flight paths. NOTE: As this blog series is focused on establishing a baseline knowledge level for further discussions about current concerns for airports and communities, this will focus on air carrier and business jet aviation. This will not focus on general aviation such as small private aircraft.


Flight procedures, paths that aircraft fly through the sky from airport to airport, are provided to most pilots through two means: 1) paper charts, and 2) digitally in their aircraft navigation systems. These aircraft navigation systems are an onboard computer, outlined in the red circles in Figure 1, that contain a database from which the pilot selects an Air Traffic Control (ATC) assigned path. This onboard computer, known as a Flight Management System (FMS) then sends navigation commands to the aircraft’s navigation displays. Additionally, the FMS receives inputs from GPS satellites to assist in the location and navigation along the flight procedure.

Figure 1. Flight Management Computer (FMS) sends flight commands to the aircraft’s
navigation displays to assist the pilot fling the Flight Procedure assigned by ATC.


When the pilot is preparing the aircraft for flight, they will enter the ATC provided flight procedures into the FMS. They will then confirm the FMS displays on the navigation screens in front of the pilots. Once satisfied that the flight displays are programmed correctly per the ATC clearance, they will proceed to the runway for takeoff. An important point to make here is that the FMS only displays the flight procedure from the database within its memory. It does not have an ability to show other FYI items that might be of concern to local communities such as noise monitors, areas to avoid, houses, etc. The FMS only displays the ATC cleared flight path for the pilots to reference.


In the next blog, we will identify the takeoff profile of an aircraft using the FMS programmed flight procedures. This is a more complicated procedure that it appears on the surface and has implications on community expectations surrounding the airport.


About the Author:

Grady Boyce is a current and active Captain for a major airline flying the B-737. He has participated in, and led, airspace developments and ATC modernization efforts on all continentsexcept Antarctica. Grady is a consultant to BridgeNet bringing flight procedure development, ATC expertise, and TERPS assistance into their current and future activities.