Boeing 737Max, l’enchaînement des modifications marginales aboutit à une catastrophe (deux catastrophes ?) Sous la pression de la réduction des coûts, un bricolo dans le logiciel de contrôle de vol a été introduit et de ne pas en informer les pilotes (il aurait fallu les faire repasser au simulateur de vol pour les habiliter au nouveau système…)
After a Lion Air 737 Max Crashed in October, Questions About the Plane Arose - The New York Times
Boeing’s 737 Max is the latest version of a plane that first went into service half a century ago.
Credit : Matt Mcknight/Reuters
But Boeing’s engineers had a problem. Because the new engines for the Max were larger than those on the older version, they needed to be mounted higher and farther forward on the wings to provide adequate ground clearance.
Early analysis revealed that the bigger engines, mounted differently than on the previous version of the 737, would have a destabilizing effect on the airplane, especially at lower speeds during high-banked, tight-turn maneuvers, Mr. Ludtke said.
The concern was that an increased risk of the nose being pushed up at low airspeeds could cause the plane to get closer to the angle at which it stalls, or loses lift, Mr. Ludtke said.
After weighing many possibilities, Mr. Ludtke said, Boeing decided to add a new program — what engineers described as essentially some lines of code — to the aircraft’s existing flight control system to counter the destabilizing pitching forces from the new engines.
That program was M.C.A.S.
The F.A.A. would also determine what kind of training would be required for pilots on specific design changes to the Max compared with the previous version. Some changes would require training short of simulator time, such as computer-based instruction.
“I would think this is one of those systems that the pilots should know it’s onboard and when it’s activated,” said Chuck Horning, the department chairman for aviation maintenance science at Embry-Riddle Aeronautical University.
That was not the choice that Boeing — or regulators — would make.
The F.A.A. Sides With Boeing
Ultimately, the F.A.A. determined that there were not enough differences between the 737 Max and the prior iteration to require pilots to go through simulator training.
While the agency did require pilots to be given less onerous training or information on a variety of other changes between the two versions of the plane, M.C.A.S. was not among those items either.
At least as far as pilots knew, M.C.A.S. did not exist, even though it would play a key role in controlling the plane under certain circumstances.
Boeing did not hide the modified system. It was documented in maintenance manuals for the plane, and airlines were informed about it during detailed briefings on differences between the Max and earlier versions of the 737.
But the F.A.A.’s determination that the system did not have to be flagged for pilots gave pause to some other regulators.
Across the Atlantic, the European Aviation Safety Agency, the European Union’s equivalent of the F.A.A., had qualms, according to a pilot familiar with the European regulator’s certification process.
At first, the agency was inclined to rule that M.C.A.S. needed to be included in the flight operations manual for the Max, which in turn would have required that pilots be made aware of the new system through a classroom or computer course, the pilot said. But ultimately, he said, the agency did not consider the issue important enough to hold its ground, and eventually it went along with Boeing and the F.A.A.