From FlightGlobal:
Test pilots on the Boeing 787 encountered the dormant throttle phenomenon at the centre of the Asiana 777 crash inquiry, the hearing into the accident has shown.
It has also revealed that the European Aviation Safety Agency had noted the behaviour logic following a series of familiarisation flights on the 787 in May 2011.
Delegates at the National Transportation Safety Board hearing into the Asiana crash, which is exploring automation issues, had heard that the 777’s flight-level change mode – normally only used in cruise – was activated during the final approach to San Francisco.
As a result of the aircraft’s system logic, the mode change effectively left the autothrottle in an unresponsive “hold” state when the pilot disengaged the autopilot and retarded the thrust to idle.
The airspeed of the 777 bled away, with no increase in thrust, and the aircraft sank before colliding with a sea wall short of the runway.
Boeing’s 787 shares a number of cockpit characteristics with the 777 and the two have a common type rating.
US FAA acting assistant manager, transport airplane directorate, Stephen Boyd told the hearing that, during a 787 test flight, an FAA pilot had initiated a flight level change which was then interrupted by a traffic-avoidance event.
Boyd said the autothrottle similarly entered a hold mode and the test pilot, upon realising that airspeed was decaying, let the situation continue to “see what would happen”.
“Our test pilot believed that the autothrottle would ‘wake up’, not realising that the autothrottle…would not ‘wake up’. It was already awake,” added Boyd. The pilot eventually added thrust to bring the airspeed back and continue the flight.
EASA had similarly noted that the autothrottle ‘wake up’, which acts as an airspeed-protection feature, is inoperative during certain automation modes – including flight-level change mode with the autothrottle on hold.
In its debriefing document following six 787 validation flights in May 2011, EASA stated that, while the ‘wake-up’ feature is not required for certification, its absence under certain conditions might be considered an “inconsistency” from the pilot’s perspective.
“Inconsistency in automation behaviour has been in the past a strong contributor to aviation accidents,” it added. “The manufacturer would enhance the safety of the product by avoiding exceptions in the ‘autothrottle wake-up’ mode condition.”