Airbus To Correct A220 Autothrottle Imperfection

LYON—Airbus is working on improving the A220’s autothrottle design, after several reports of crew errors that could have led to a tail strike or more serious incidents. 

The aircraft’s autopilot will be modified, too. In the meantime, procedures are temporarily added in the takeoff phase.

An autothrottle enables the pilot to control power in a smarter way than manually. Typically, the system can adjust fuel flow to attain a specified speed. It therefore helps with pilot workload, fuel consumption and engine life.

On the A220, it happened that the autothrottle unexpectedly disengaged during takeoff. While attempting to reengage the autothrottle during the takeoff roll, some crews inadvertently selected the autopilot.

Inadvertent autopilot engagement may have serious consequences, Airbus says in an article published in its Safety First online magazine. Such an action may result in early rotation that can lead to a tail strike, inability to climb, runway overrun, or even loss of control.

In one event, when the crew mistakenly pressed the autopilot switch, the aircraft started to rotate. At 110 kt, speed was 27 kt below the computed rotation speed. The autopilot nevertheless commanded a pitch-up to reach the flight guidance pitch target. The sequence of events suggests the pilot flying’s immediate inputs were only partly right. The pitch attitude reached 10.7 deg. and the aircraft therefore came 1-2 ft. close to a tail strike, Airbus reckons. After some corrective inputs, the aircraft eventually took off eight kt below the computed speed. The crew continued the flight.

Such a situation can be avoided by design, the airframer’s engineers have determined. To prevent autopilot engagement during the takeoff roll, the Primary Flight Control Computer will be upgraded to inhibit autopilot engagement until six seconds after liftoff. The improvement will be introduced in the second quarter of 2024.

As for the autothrottle, its disconnect logic is being updated. The issues that caused it to disconnect during the takeoff roll will be addressed, Airbus says, falling short of giving a time frame.

Finally, higher priority will be given to takeoff configuration warning messages. In the aforementioned event, the crew could have been warned about the autopilot being wrongly engaged on the ground. That alert, however, was partly hidden by the autothrottle alert.

While system enhancements are being designed, Airbus has issued operational changes to prevent the event from happening again. From now on, the pilots must not attempt to select and engage the autothrottle during the takeoff roll. This will reduce the risk of unintentional selection of the autopilot switch, Airbus says.

Managing an autothrottle disconnect during takeoff is more complex. Depending on the speed, autothrottle takeoff mode and engine rotational speed, the crew should continue or abort takeoff.