Boeing to warn 737MAX operators, a potential instrument failure, following the fatal crash of a Lion Air flight 610, killing all 189 passengers onboard.
According to Seattle times, Boeing was preparing a service bulletin, Tuesday evening to warn all its new 737 MAX operators of the potential for an instrument failure that could result in the plane entering a dangerous dive.
FAA is expected to follow the Boeing’s service bulletin and issue a mandatory “airworthiness directive” in the coming days.
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.
“In particular, with the sensor falsely indicating that the nose is too high, when it isn’t, it causes an automatic system response that “trims” the horizontal tail of the plane to begin putting the plane’s nose down. At the same time, it causes an indicator of the minimum speed to tell the pilot that the plane is near a stall, which also causes the pilot’s control column to shake as a warning. And the air-speed indicators on both sides of the flight deck disagree.”….“If the nose is trimmed down on an aircraft, it becomes difficult for the crew to hold it,” said the person briefed on Boeing’s bulletin to Seattle times.
Based on the SB, lion air flight, “For 12 minutes before it crashed, the altitude swung up and down as if the pilots were fighting to maintain height, bringing the plane up, then having it swing down again repeatedly.”
On 6 November, Boeing issued an Operations Manual Bulletin (OMB) directing 737MAX operators to address circumstances where there is erroneous input from an AOA (Angle Of Attack) sensor on Boeing 737 MAX aircraft.