What is the trim wheel behavior on the A320 family?

The Trim Wheel in the A320s usually is moving by itself, representing the current stabilizer position (or rather command). Before takeoff I believe it is set by hand to set the takeoff trim.

During flight it is not touched unless the aircraft goes into direct law or "worse".

What happens though if the pilot touches the trim wheel in normal law?

Will the aircraft shift into another Law where manual trim can be used? Will it move the stabilizer to the position set by the pilot and then adjust back to where it would usually be, possibly turning off any AP that is engaged? Will the aircraft ignore the manual input?

1 Answer

Before takeoff I believe it is set by hand to set the takeoff trim.

Correct.

The trim wheels always have priority over the electrical trim. Moving them in-flight:

• Bypasses the flight computers (an override mechanism with micro-switches).
• Disconnects the autopilot when moved beyond a certain threshold.
• Freezes the automatic trim.

The flight computers for normal stabilizer control (ELACs) remain active though, no change in laws would take place. They remain active to ensure they're synchronized with the manual action. Let go of the trim wheels, use the stick again in pitch, and auto trim will resume.

If you use the stick, while holding tight on the wheels, the flight computers will think the stabilizer is jammed, and the warning STABILIZER JAM will show, with it the associated procedure.

During flight it is not touched unless the aircraft goes into direct law or "worse".

There are two scenarios where you'd need them that are better (not worse) than direct law. That is the aforementioned [actual] stabilizer jam, or F/CTL STABILIZER JAM. The latter is when the flight computers lose contact (electrical signal) with the stabilizer (this scenario leads to alternate law with protections lost).

In both scenarios, if the pilot is able to move the trim wheels, they'll use the elevator position shown on the flight controls display to make trim inputs such that the elevator moves to the neutral position.

Source: A320 FCOM (don't use for flight).

• Can you show where in the FCOM you found that information for further reading, please? – Maverick283 Mar 28 at 12:51
• @Maverick283: Typically I add the quotation if the information is from one place, but the findings I presented are from multiple places, which makes for clunky presentation. However, check now as I added screenshots (adding the QRH elements would be too much though). – ymb1 Mar 28 at 13:05
• Perfect, thanks a lot for your effort! – Maverick283 Mar 28 at 13:07