As a result of continuing investigations into last week’s crash of Lion Air flight 610, the US Federal Aviation Administration has issued an emergency airworthiness directive (AD) to operators of Boeing 737 MAX aircraft calling on them to address procedures in the event of pilots receiving erroneous angle of attack sensor information.
“This emergency AD was prompted by analysis performed by the manufacturer showing that if an erroneously high single angle of attack (AOA) sensor input is received by the flight control system, there is a potential for repeated nose-down trim commands of the horizontal stabiliser,” the AD, issued on Wednesday evening (US time), reads.
“This condition, if not addressed, could cause the flightcrew to have difficulty controlling the airplane, and lead to excessive nose-down attitude, significant altitude loss, and possible impact with terrain.”
The FAA says the AD is an interim action, and “if final action is later identified, we might consider further rulemaking then”.
“This AD requires revising certificate limitations and operating procedures of the airplane flight manual (AFM) to provide the flightcrew with runaway horizontal stabiliser trim procedures to follow under certain conditions.”
The AD followed Boeing’s issuing of an operations manual bulletin (OMB), asking 737 MAX operators to remind pilots of how to handle “erroneous” information from the aircraft’s angle of attack sensors.
“The Indonesian National Transportation Safety Committee has indicated that Lion Air flight 610 experienced erroneous input from one of its AOA (angle of attack) sensors,” Boeing said in a statement on its website on Wednesday.
“On November 6 2018, Boeing issued an operations manual bulletin (OMB) directing operators to existing flightcrew procedures to address circumstances where there is erroneous input from an AOA sensor.”
The investigation into the loss of the two-month-old Lion Air 737 MAX 8, which crashed into the sea off the coast of the Indonesian capital Jakarta after a high-speed dive with the loss of all 189 passengers and crew on board, is being led by the Indonesian National Transportation Safety Committee, which has found that the aircraft had experienced airspeed indicator malfunctions on its last four flights.
Attempts to fix the issues were unsuccessful, NTSC chairman Soerjanto Tjahjono has said, with the pilots of the 737’s second-to-last flight experiencing conflicting information despite an AOA sensor being replaced.
“The point is that after the AOA [sensor] is replaced the problem is not solved, but the problem might even increase. Is this fatal? NTSC wants to explore this,” he is reported as saying.
The 737’s flight data recorder was recovered last Thursday, while the search for the aircraft’s cockpit voice recorder, hampered by the muddy seabed, is continuing.