A recently discovered document proves that Boeing ignored requirements international regulators made when they certified Boeing's 737 MAX airplane.
After the recent Boeing 737 MAX incident in Ethiopia we explained why it happened. Even before the plane type was grounded by the FAA we wrote:
Our early take was confirmed by the reporting of other media which we also discussed:
The basic problem:
For commercial reasons Boeing wanted the new 737 version to handle like the old ones. But changes in the new version required an additional system to handle certain flight situations. The development of that system and the safety analysis of its implications were rushed through. Pilots were not informed of it and not trained to counter its failure.
The added 'maneuver characteristics augmentation system' (MCAS) depended on only one sensor. When the sensor provided false data MCAS engaged and pointed the planes towards the ground. Manual trim using the plane's trim wheel was required to regain flight stability. The pilots were not aware of that. The regulators who certified the plane as safe were unaware of the extend of the problem:
The MCAS system is poorly engineered and the design should never have been certified in the first place. But the issue is even worse. The certification that was given relied on false data.
The first MCAS design, on which the safety analysis and certification was based, allowed for a maximum trim movement by MCAS of 0.6 degree of a maximum of 5 degree. Flight tests proved that to be too little to achieve the desired effects and the maximum movement was changed to 2.5 degree.
No safety analysis for the much greater movement was conducted. The FAA and foreign regulators were not informed of it. Their certification of the 737 MAX was based on misleading data.
But even those certifications were only conditional. They required from Boeing to include relevant training material that explained the MCAS trim system and its potential problems to the pilots.
The original certification for the 737 MAX was issued by the U.S. regulator FAA. The European regulator EASA based its certification on the one the FAA provided but it added several of its own requirements. There is now documentary evidence that Boeing neglected to fulfill at least one of those requirements.
Page 15 of the Explanatory Note discusses "Longitudinal trim at Vmo". Vmo is the maximum operational speed. The trim sets the nose of the plane up or down, independent of other pilot input. Too high up and the plane with lose lift and stall, too low down and the plane will hit terrain.
A failure of the MCAS system could trim the nose down. As a countermeasure the pilots would have to switch the trim system off. They would then manually trim the plane back into a level flight. This was a concern. The EASA note says:
Subsequent to flight testing, the FAA-TAD expressed concern with compliance to the reference regulation based on an interpretation of the intent behind "trim". The main issue being that longitudinal trim cannot be achieved throughout the flight envelope using thumb switch trim only.
EASA considered the need to use manual trim "unusual". But it allowed it to pass because the required training material would "clearly explain" the issue:
The need to use the trim wheel is considered unusual, as it is only required for manual flight in those corners of the envelope.