What does the Airbus A320 FCU do, and how do you use it?

The Airbus A320 Flight Control Unit (FCU) is the glareshield panel used to set and engage flight-guidance targets and modes: speed/Mach, heading/track, altitude and vertical speed/flight-path angle. Pilots push or pull its selectors to choose managed FMS guidance or selected targets, then confirm the aircraft’s actual response on the PFD Flight Mode Annunciator.

For Aviation & Real-World Flying readers, this explanation follows standard A320-family logic and then applies it to flight simulation. Detailed add-ons reproduce most of that logic closely; simplified aircraft may omit modes, change mouse interactions or model only part of the push/pull behaviour.

What does the Airbus A320 FCU control?

The FCU controls the aircraft’s immediate flight-guidance targets rather than building the flight plan itself. It works with the Flight Management and Guidance System, flight directors, autopilots and autothrust.

• Speed or Mach: selects a manual target or returns control to the managed speed calculated by the FMGS.
• Heading or track: commands a selected direction or returns the aircraft to managed NAV guidance along the active route.
• Altitude: sets the cleared altitude and initiates managed or open climb and descent modes.
• Vertical speed or flight path angle: commands a specific rate of climb or descent, or an angular flight path when TRK/FPA is selected.
• AP1, AP2 and A/THR: control the autopilots and autothrust system.
• LOC and APPR: arm the applicable localiser and approach guidance modes.

The HDG-V/S and TRK-FPA selector changes the paired references used by the lateral and vertical windows. Flight director switches are normally on the adjacent EFIS control panels rather than the central FCU itself. Some aircraft standards also include an EXPED function for expedited climb or descent, but its availability and simulation vary.

The MCDU is the interface used to enter route, performance and approach data into the FMGS; the FCU gives tactical commands during the flight. Managed guidance therefore depends on suitable FMGS data, covered in our guide to setting up the A320 route and performance data in the MCDU.

How do the A320 FCU push and pull controls work?

Pulling a selector normally takes direct control with a selected target, while pushing it normally returns guidance to the aircraft’s managed system. The useful mnemonic is “pull towards the pilot, push towards the aircraft”, but the vertical-speed selector is an exception.

Turning a knob does not necessarily engage the displayed value. Speed, heading and vertical-speed values can be preselected temporarily, while changing the altitude window does not by itself choose a new vertical mode. This is why rotating a selector and waiting for the aircraft to respond is such a common simulator mistake.

On a conventionally modelled FCU, dashes and an illuminated dot indicate managed operation in the speed and heading windows. Even then, the definitive source is the Flight Mode Annunciator at the top of the PFD: green modes are active and blue modes are armed. Our explanation of the A320 PFD and its mode annunciations shows where to check.

How do you use the Airbus A320 FCU?

Use a three-part discipline for every FCU change: set the target, engage the required mode, then verify the result on the FMA.

1. Prepare the managed guidance. If you intend to use NAV, managed climb, managed descent or managed approach guidance, check that the active route has no unwanted discontinuity and that the required performance and approach data are present.
2. Check the automation state. Select the relevant flight directors and A/THR as required. AP1 or AP2 can follow the same guidance commands; routine flight normally uses one autopilot rather than both.
3. Set the cleared altitude. Rotate the altitude selector to the altitude authorised by ATC or required by your procedure. Treat this as a limit: managed guidance will not deliberately continue through the FCU altitude.
4. Choose lateral guidance. Leave or return to NAV for the programmed route. For ATC vectors, weather avoidance or circuit work, rotate the heading or track selector and pull it.
5. Choose the speed target. Use managed speed for a correctly programmed departure, climb, cruise or approach profile. Pull selected speed for an explicit ATC assignment, spacing requirement or training exercise.
6. Select the vertical mode. Push the altitude selector for managed climb or descent, pull it for open climb or descent, or select and pull V/S-FPA when a particular rate or angle is required.
7. Read the FMA. Confirm both the active mode and any armed follow-on mode. Do not make the next input until the aircraft has accepted the first one.

A worked example of these actions in context appears in our complete Microsoft Flight Simulator A320 flight procedure.

How do you start an A320 descent with the FCU?

Set a lower cleared altitude first, then choose the descent mode that matches the situation. Merely lowering the altitude window while level does not initiate a descent.

• Push for managed DES when the route and vertical profile are valid and you want the FMGS to account for programmed altitude and speed constraints.
• Pull for OP DES when you need a direct descent towards the FCU altitude without observing intermediate flight-plan altitude constraints.
• Select and pull V/S when ATC assigns a rate or you need precise short-term path control. Monitor speed closely because an excessive rate can cause the aircraft to lose or gain energy faster than thrust can correct it.

After the input, look for DES, OP DES or V/S on the FMA. As the aircraft captures the selected altitude, the vertical mode will normally change through an altitude-capture indication such as ALT* before settling in ALT.

Does the FCU work with the autopilot off?

Yes. With the relevant flight director on, the FCU’s lateral and vertical commands appear as guidance on the PFD for manual flying. A/THR may also continue controlling speed or thrust as appropriate to the active mode.

An FCU speed target is not always a simple throttle command. In open climb and open descent, pitch controls speed while thrust follows the commanded climb or descent mode; in V/S, autothrust generally tries to maintain speed with thrust until it reaches its authority or operating limits.

When should you use selected mode instead of managed mode?

Use selected mode for immediate tactical control and managed mode when a valid flight plan should drive the aircraft.

• Choose selected heading or track for vectors, weather avoidance, visual manoeuvring or recovery from a poor active route. Selected heading does not rewrite the flight plan; intercept the desired leg and push for NAV when appropriate.
• Choose selected speed for an explicit assigned speed or close spacing. Published speed restrictions correctly entered in the FMGS are usually better handled in managed speed.
• Choose OP CLB or OP DES when an unrestricted climb or descent to the FCU altitude is needed. These modes disregard intermediate FMGS altitude constraints.
• Choose V/S or FPA for an assigned vertical rate, a controlled shallow descent or short-term path correction. Avoid using a large V/S command to rescue a badly planned descent.
• Choose managed modes for normal route tracking, constraint-aware climb and descent, and properly prepared arrival or approach guidance.

Why is the A320 FCU not doing what you selected?

Most apparent FCU failures are mode-selection, flight-plan or simulator-interaction problems rather than faults in the panel.

• The value changed but the aircraft did not respond. You probably turned the selector without pulling or pushing it. Check whether the FMA still shows the previous mode.
• The altitude changed but the aircraft stayed level. The altitude window is a target and clearance limit, not a climb or descent command. Engage managed, open or V/S guidance.
• NAV will not engage or capture. Check for an invalid active leg, route discontinuity or unsuitable intercept. Use selected heading to establish a sensible intercept, repair the route or activate the correct leg.
• Managed descent behaves unexpectedly. The aircraft may be above or below its computed profile, or the FMGS may lack suitable performance, constraint or arrival data. Use an appropriate selected mode while correcting the setup.
• Speed decays or runs away in V/S. The commanded vertical rate may exceed the aircraft’s available energy. Reduce the rate and consider managed or open descent instead.
• LOC or APPR does not capture. These buttons arm guidance; they do not force the aircraft onto the beam. Verify the approach data or tuning, localiser reception and a sensible intercept. Glideslope capture should normally be approached from below.
• The autopilot itself will not engage. That can involve aircraft state, control inputs, failures or add-on configuration rather than the FCU target. Work through our checks for an autopilot that refuses to engage in Microsoft Flight Simulator.
• The knob will rotate but not push or pull. Mouse hotspots and cockpit interaction systems vary between simulators and add-ons. Use the displayed cockpit tooltip and verify that hardware bindings send the aircraft-specific push, pull or managed-mode event rather than only increasing or decreasing the value.
• The aircraft uses simplified Airbus logic. Some default or lighter models omit mode transitions or combine commands. Trust the FMA and the model’s documented behaviour rather than assuming every real-aircraft function is represented.

Our practical rule is simple: set the target, choose selected or managed guidance, and verify the FMA. That prevents most FCU errors before they develop into route, speed or altitude deviations.