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Investigators who are investigating the causes of the Lion Air crash in Indonesia last week have discovered a potential failure of a sensor on a jet plane.
Following the fatal crash of a Lion Air aircraft in Indonesia last week, Boeing was preparing Wednesday night to warn all airlines operating its new 737 MAX of the risk of instrument failure that could result in diving into a dangerous dive informed about the details of the newsletter.
The warning is in the form of a service bulletin addressed to all operators of the aircraft and containing instructions indicating exactly what the pilots should do if the situation arises.
It is normal for the Federal Aviation Administration to follow such a warning with an "Airworthiness Directive" which makes it mandatory, which is expected in the coming days.
Investigators who study the causes of the Lion Air accident have identified a potential failure of a sensor that notifies the pilot and the flight control computer of the "angle of attack". "attack" of the aircraft, which is the angle between the wing of the aircraft and the airflow that it passes through.
An airplane will have a high angle of attack when climbing. An angle that is too high will cause a stall.
The concern about the flight model and the initial investigation of the Indonesian accident is that the sensor could possibly provide false information on this angle to the flight computer, which would trigger others.
In particular, when the sensor falsely indicates that the nose is too high, it triggers an automatic response from the system that "cuts" the aircraft's horizontal tail to begin to fold the nose of the aircraft.
At the same time, a minimum speed indicator indicates to the pilot that the aircraft is close to a stall, which also causes the pilot's control column to tremble. And the air speed indicators on both sides of the cockpit are at odds.
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Pilots may use extra force to correct the nose-down compensation, but the failure condition is repeated, so that the leaning thrust starts again 10 seconds after the correction.
"If the nose of an airplane is cut, it becomes difficult for the crew to hold it back," said the informed person of Boeing's newsletter. "The nose goes down and they have to fight it. It takes a lot of effort to prevent it from diving. Especially if your crew is confused and does not know what's going on. "
This description corresponds exactly to the type of flight of the Lion Air jet that crashed.
For 12 minutes before the crash, the altitude went up and down as if the pilots were trying to maintain the height, making the plane go up and down several times.
Pilots are usually trained to handle a tricky situation, said the Boeing newsletter's informed person, but it's with everything else that works as it should. In this case, the control column jolts, the stall warning and the speedometer clash combine to create confusion and occupy the busy drivers.
In its bulletin, Boeing tells pilots that if this failure occurs, "larger control forces may be needed to overcome any dive stabilization compensation." The instructions then indicate that after stabilization, the system automatically clears the horizontal tail off and any compensation performed manually.
"All this comes from the Indonesian accident," said the informed person of Boeing's newsletter. "I am not aware of any other operator having this problem."
More than 200 MAXs are in service worldwide.
