Category: How flying works
How to Read the FMA: Autopilot Mode Boxes on an Airliner Display
Short answer
The flight mode annunciator (FMA) is the row of mode boxes on an airliner's primary flight display. It shows which modes the autothrottle and autopilot are using now (engaged) and which will take over next (armed).
Autopilot, autothrottle and flight director
An airliner has three linked kinds of automation. The autopilot moves the flight controls. The autothrottle, or autothrust, controls engine thrust, for example to hold a set speed. The flight director only shows steering cues that tell the pilot how to fly a path. Each works in modes, such as holding a heading or following a radio beam.
Try it yourself
Look at the three FMA boxes and the white lines under them, then say what is engaged, what is armed and what just changed.
Engaged and armed modes on the FMA
The flight mode annunciator (FMA) sits on the primary flight display (PFD), the main screen in front of each pilot. FAA design guidance says it must show clearly what the system is doing now (engaged modes) and what it will do next (armed modes).
In the layout used here, three boxes run along the top: autothrottle, roll and pitch, from left to right. Green means engaged: happening now. A white line under a box means armed: it engages by itself when its condition is met. A changed mode is boxed for about 10 seconds. Colours, names and positions differ between aircraft types.
Example: the FMA during an ILS approach
An instrument landing system (ILS) has two radio beams: the localizer for left-right guidance and the glideslope for up-down guidance, normally at 3°. With the autopilot flying (CMD), the FMA can read MCP SPD, HDG SEL and ALT HOLD: hold the set speed, fly the set heading, hold the current altitude. Arming the approach adds VOR/LOC in white under HDG SEL and G/S under ALT HOLD.
At the localizer, VOR/LOC turns green and HDG SEL disappears. At the glideslope, G/S turns green and ALT HOLD disappears: the aircraft descends on the beam while the autothrottle holds the speed. Depending on airline procedures, the pilots call each change aloud, such as "Localizer captured".
Why reading the FMA matters
The automation does what its active mode says, not what the crew expects. Believing the wrong mode is active can make the aircraft do something unplanned: this is mode confusion. A 2013 FAA-sponsored working group found such errors still occur, with mode selection errors cited in 27 percent of the accidents it reviewed. FAA guidance tells pilots to check the FMA after every mode selection.
Common mistakes and myths
- Trusting the button instead of the FMA. A pressed button only shows a request; the FMA shows what the system is actually doing.
- Treating an armed mode as active. Until it turns green, the previous mode is still flying the aircraft.
- Assuming an approach mode will land the aircraft. Automatic landing needs extra equipment, approval and procedures.
Questions people ask
What does FMA stand for in aviation?
Flight mode annunciator: the strip of mode boxes on the primary flight display that shows which modes the autothrottle, autopilot and flight director are using now and which are armed to take over next.
What is the difference between armed and engaged?
An engaged mode is controlling the aircraft now. An armed mode is selected but waiting for its condition, such as reaching the localizer beam. Then it engages by itself and the previous mode drops out.
Is the FMA the same in every airliner?
No. The purpose is the same, but colours, mode names and box positions differ between aircraft types. This page describes the AeroFox airliner: autothrottle, roll and pitch boxes from left to right, green for engaged and white for armed.
Practise it in the simulator
In the free Read the FMA lesson, you engage the autopilot, arm an ILS approach and read five mode changes as they happen.
Related explainers
Sources
- Advisory Circular 25.1329-1C, Approval of Flight Guidance Systems (2014) (FAA)
- Advisory Circular 120-71B, Standard Operating Procedures and Pilot Monitoring Duties (2017) (FAA)
- Operational Use of Flight Path Management Systems, PARC/CAST Flight Deck Automation Working Group final report (2013) (FAA)
- Aeronautical Information Manual, chapter 1 section 1 (1-1-9 Instrument Landing System) (FAA)
- Advisory Circular 120-118, Criteria for Approval/Authorization of All Weather Operations (2018) (FAA)
About these explainers
AeroFox is a free, public-interest project with no paid features. The explainers are written by the AeroFox team from public sources such as FAA handbooks, NASA and regulators, and, for the lessons from the news, from the news reports we link to. Each page lists its sources, and pages are updated when the facts or the lessons change. They explain ideas. They are not flight instruction, medical advice or legal advice, and they do not count toward any licence.