Boeing admits 737 Max sims didn't accurately reproduce what flying without MCAS was like

Turning off trim control software in training wouldn't give realistic results – report

Boeing has admitted that pilot training simulators for the controversial 737 Max did not accurately reproduce what happened if the infamous MCAS system went gaga.

In a statement, the American aircraft manufacturer said it had "made corrections to the 737 MAX simulator software and has provided additional information to device operators to ensure that the simulator experience is representative across different flight conditions".

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The US Wall Street Journal newspaper reported over the weekend that simulators used for pilot training "did not reflect the immense force that it would take for pilots to regain control of the aircraft" after disabling electronically assisted trim controls.

Those controls interfaced with MCAS, the Manoeuvring Characteristics Augmentation System. As reported extensively here and elsewhere, MCAS was intended to automatically kick in and help prevent the 737 Max from stalling – falling from the sky, basically – in a particular flight scenario where the aircraft's angle of attack (AoA) becomes too high. It does so through adjusting the airliner's trim, pushing the aircraft's nose down in 10-second bursts.

After two fatal crashes that killed all aboard, it emerged that pilots were not made aware of what MCAS was, how it worked or – after the second crash – how to safely disable it. Boeing instructions after the first crash were to disable the electric stabiliser trim motors, preventing MCAS from operating at all. However, that led to pilots being forced to rely on the manual backup trim: a great big mechanical wheel in the cockpit.

Theories are circulating that the crew of the second fatal crash, Ethiopian Airways flight ET302, after successfully cutting out the electric stab trim per Boeing's instructions, were then unable to move the trim wheel against the huge aerodynamic forces caused by their airliner accelerating towards the ground. As speed increases, so does the force needed to move control surfaces, much as the wind pressure you feel when putting your hand out of a car window at speed.

If Boeing-approved 737 Max flight simulators were not correctly reproducing those forces on the mechanical trim wheel, pilots could have been being lulled into a false sense of security while practising emergency drills on the ground.

Updates coming but airlines aren't convinced

Boeing also said it had finished testing a software update it claims will fix the MCAS problem, as well as having provided "additional information to address Federal Aviation Administration (FAA) requests that include detail on how pilots interact with the airplane controls and displays in different flight scenarios. Once the requests are addressed, Boeing will work with the FAA to schedule its certification test flight and submit final certification documentation."

According to an earlier Boeing statement, the patch will do the following:

  • Flight control system will now compare inputs from both AoA sensors. If the sensors disagree by 5.5 degrees or more with the flaps retracted, MCAS will not activate. An indicator on the flight deck display will alert the pilots.
  • If MCAS is activated in non-normal conditions, it will only provide one input for each elevated AoA event. There are no known or envisioned failure conditions where MCAS will provide multiple inputs.
  • MCAS can never command more stabilizer input than can be counteracted by the flight crew pulling back on the column. The pilots will continue to always have the ability to override MCAS and manually control the airplane.

Ryanair, one of the world's biggest operators of Boeing 737s in general, has ordered a number of 737 Maxes. It said in an investor presentation (PDF) that it had "delayed the delivery of our first 5 B737-MAX aircraft to Winter 2019 (subject to regulatory approval by EASA)", adding: "We continue to have utmost confidence in these aircraft."

Similarly, Germany's TUI group is reportedly going to decide by the end of this month whether or not to abandon hopes of flying its 737 Maxes for this year's key holiday season.

Boeing itself went a full month without receiving a single new order and also deleted around 200 aircraft from its order books, according to reports, though the Paris Air Show, a big sales event, takes place next month and could see a number of new orders being placed to balance that out.

All in all, the 737 Max problems haven't gone away just yet. Software problems have big repercussions in the real world. ®




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