The NTSB investigation http://t.co/cVURqNHFJM into the Asiana 214 Boeing 777 'land short' accident at San Francisco determined that the aircraft was already high on the approach profile when the pilot flying incorrectly engaged ‘CLIMB' mode to the missed approach altitude target, causing the flight director to command the autopilot into a climb. In the normal response to this erroneous command, the pilot disengaged the autopilot and retarded thrust to idle, which had further adverse consequences.
It is interesting that Airbus fly-by-wire autopilot/flight director systems incorporate a very similar trap for pilots. Once established on final approach the SOP requires the pilot to set the missed approach altitude in the flight control unit (FCU) altitude window, in preparation for a potential go-around. However, almost every other occasion that the pilot is required to make a change to the altitude window via the adjacent rotary altitude knob, he/she must also either pull or push the knob to activate the desired vertical flight mode. Therefore there is a strong subconscious habitual demand to follow the rotary setting motion on the knob with a pull or a push – history suggests a pull is the more frequent mistaken action on approach.
Such errors are of course more likely when cockpit workload is already elevated, for example when struggling to get the aircraft back on to the required approach angle. I wonder why both manufacturers have found it necessary to ‘build in’ an obvious trap?
No comments:
Post a Comment