Russia requests Boeing to amend 747’s autopilot logic
March 29, 2017
The Boeing 747-400F jumbo jet belonging to a Turkish cargo company MyCargo Airlines crashed near Kyrgyzstan’s Manas airport on 16 January, 2017. The crash killed at least 39 people and most of the victims were the residents of a village. The 747 overshot the runway, taking it past the airport and into a residential district.
Considering the crash, Russian investigators are advising Boeing to improve autopilot logic to avoid the possibility of an aircraft’s automatically following a descent path incompatible with runway position.
According to the report from Russia’s Interstate Aviation Committee, the wide body jet had intercepted a false glide slope, above the normal 30 descent path, because it had been too high on the approach. This resulted error in flight director system which indicated the aircraft was no longer following the glideslope.
The inquiry team says that the autopilot would not have disengaged instead it would have maintained an inertial path, continuing to track a standard 30 descent path, regardless of the actual glideslope.
“The path will be maintained until a valid glideslope signal is regained or until the crew intervenes by disengaging the autopilot or initiating a go-around,” adds the inquiry.
Boeing equips its aircraft with such type of inertial-path generation capability in order to permit the autopilot to continue an approach even if glideslope or localizer signals are disrupted.
The crew of the 747 did not intervene or attempt to initiate a go-around until the decision height. The approach was complicated due to darkness and fog. Pilots allowed the aircraft to drift down even after knowing the runway was not visible. Also the aircraft autopilot’s flare mode engaged before crew commanded go-around power.
The airlines operating Boeing aircraft are recommended to increase crews’ awareness of a possible switch to inertial mode by the autopilot during a glideslope descent.