Boeing wants to get its stalled fleet of machines of the type 737 Max 8 back up with a software update. Now, the aircraft manufacturer explains to its customers, according to information from the Reuters news agency, the exact functioning of the rectification.
Two machines of the comparatively young aircraft type were crashed recently, 346 people died. In the case of the Lion Air jet, which crashed in Indonesia in October, the so-called MCAS system has been identified as the cause, and investigations into a 737 Max in Ethiopia are still ongoing. Because of clear parallels, however, experts assume that even there, the MCAS system has caused the crash.
The abbreviation, which stands for "Maneuvering Characteristics Augmentation System", hides a software that is supposed to support the pilot: Because the latest version of the Boeing 737 evergreen tends to raise its nose in some flight situations due to its new engines, the software lowers them without the pilot's intervention. So a stall and a crash of the jet should be prevented. (Read the history of the 737 Max 8 here)
In the future only limited intervention of the system
The now presented by Boeing update of this software is intended to severely limit the intervention in the future. So far, the system has been able to repeatedly lower the nose of the machine - even if the pilots pulled the machine up the stick. Evidence of this is the trajectory of the two crashed jets: a desperate up-and-down - and a fight that the pilots lost in the end.
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However, this fatal behavior of the machines was evidently not only triggered in an actual emergency - an impending stall. But also due to erroneous data of the two so-called Angle-of-Attack sensors (AOA), which continuously assess the attitude of the machine. If the MCAS in this way developed its dangerous life of its own, the pilots could only make do with a complete deactivation of the system.
That's exactly what Boeing wants to fix with his software update. In the future, the automatic position correction should not be repeated, but only done once. This should give the pilot more intervention options again.
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In addition, the system should disable itself in case of possible measurement errors. If the data of the two AOA sensors on the outer skin of the aircraft deviate too much from each other, a warning light flashes in the cockpit and the MCAS is deactivated. The warning light offered Boeing so far at delivery only for a surcharge, in the future they should belong to the basic equipment of the aircraft.
Previously, the MCAS always referred only to the data of one sensor and ignored the data of the other. A procedure that is unusual for aviation: for safety reasons, the law of redundancy applies here; in principle, everything must be present at least twice in order to compensate for the failure of a system.
The software update is currently being reviewed by the US aviation authority FAA. Only when the release is granted, it can be loaded and restart the 737 Max fleet.