WASHINGTON — The Federal Aviation Administration revealed two of 38 Airbus A220 take-off incidents were nearly catastrophic. The unintentional autopilot engagement requires additional precautionary measures to prevent a recurrence, the US regulator says.
According to the incident report, the crew attempted to re-engage a detached autothrottle but accidentally activated the autopilot, causing the A220 to rotate below the V1 decision speed."This resulted in a low-energy take-off, which is extremely hazardous as it could lead to the [aircraft] stalling [or] impacting terrain," says the FAA in a 22 November directive.
The A220's autopilot and autothrottle buttons are located directly one above the other in the center of the mode control panel."The control panel for autothrottle and autopilot engagement is structured in such a way that it is possible for the flight crew to mistakenly engage the autopilot when attempting to re-engage the autothrottle," says the FAA.
Activation of the autopilot is restricted below 400ft. The FAA states that the autothrottle is prone to disconnect during turbulence because the airspeed information comes from a different source rather than the flight control system monitor. Different sources for pressure altitude between systems are likely to cause a disconnection due to inconsistent data.
Transport Canada has already ordered the Airbus A220 operators to make the necessary changes in flight manuals to keep pilots alerted that accidental autopilot engagement could cause premature rotation, tail strike, inability to climb, or a stall. But the FAA's directive goes beyond it by mandating an inclusion in the manual – the prohibition of selecting or re-selecting the autothrottle once the thrust levers have been pushed to the take-off setting.The prohibition will apply until the aircraft reaches at least 400ft above the ground, the threshold for autopilot engagement.
