Investigators have carried out a series of observations to examine whether pilots of an Atlas Air Boeing 767-300 freighter could have accidentally activated a go-around switch while operating other flight controls.
The 767 entered go-around mode while descending for approach to Houston on 23 February, apparently triggering an in-flight upset during which the aircraft was pushed into a steep dive.
While the US National Transportation Safety Board has not conclusively established the reason for the go-around activation, it has examined various human factors scenarios using a 767 simulator in Miami.
Along with the NTSB, representatives from Boeing and Atlas Air took part in the simulations which replicated the aircraft’s approach path to Houston.
Part of the study monitored various hand and arm positions of the captain and the first officer as they operated controls – including the captain’s reaching behind the throttles to grasp the flap lever on the right, and the first officer’s similarly reaching to activate the speedbrake on the left.
The tests considered not only accidental interference from the pilots’ arms but also the possibility that a go-around switch – located on the rear of the thrust levers – could have been brushed by a wristwatch, or bumped during turbulence.
No specific evidence has emerged of such a scenario, but the inquiry notes that air traffic control had instructed the aircraft to expedite a descent to 3,000ft about 2min before the go-around mode activation, and that the speedbrake was subsequently extended.
Atlas Air’s crew operating manual recommends that the flying pilot should keep their hand on the speedbrake while in use, to prevent its being left extended when no longer required.
The inquiry says the speedbrake was recorded as retracting a few seconds after the go-around mode activation, and just before the crew reacted with initial exclamations over the aircraft’s unexpected behaviour.
Atlas Air has not received any safety reports, prior to the accident or since, describing inadvertent activation of go-around mode on the 767. The carrier’s crew operating manual does not have specific procedures for inadvertent selection of a go-around switch.
Investigators obtained provisional information on other inadvertent go-around selection incidents through a request to NASA’s aviation safety occurrence database. While the extent of such events is not clear, the request returned data on 11 incidents involving various aircraft types.
The inquiry is still analysing the findings from the simulator human factors study.
Simulation exercises were also carried out to assess the forces needed to override the autopilot and stop trim activation during an inadvertent go-around, check autopilot and autothrottle indications, and document stall-recovery techniques.