Proposed US fix for Boeing 737 Max software woes does not address Ethiopian crash scenario, UK pilot union warns

MCAS saga still hasn't ended as reps warn of trim wheel problem

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The British Airline Pilots' Association (BALPA) has told American aviation regulators that the Boeing 737 Max needs better fixes for its infamous MCAS software, warning that a plane crash which killed 149 people could happen again.

Airlines, in contrast, are broadly happy with proposed changes to the Boeing 737 Max, even as trade unions bellow at the US Federal Aviation Administration (FAA) that more needs to be done.

In public comments submitted to the FAA's notice of proposed rulemaking (NPRM), BALPA warned that one of the proposed workarounds for a future MCAS failure could lead to a repeat of the crash of Ethiopian Airlines flight ET302.

MCAS – Manoeuvring Characteristics Augmentation System – is a software system intended to counteract the effect of hanging bigger and more powerful engines off the Boeing 737 airframe. The new engines gave the airliner different flying characteristics from previous models. With Boeing relying on regulators certifying the 737 Max as an incremental advance rather than a whole new design, MCAS was necessary to get it through FAA certification without regulators imposing expensive training requirements on the new aircraft before pilots could fly it.

The NPRM, published here, proposes various fixes to the 737 Max design, its software and procedures for pilots to follow in the event of a problem. One of those procedures includes disabling the airliner's automatic trim system, operated by MCAS when the software kicks in, and having the two pilots use a manual backup trim wheel instead of the aircraft's powerful electric motors.

BALPA said: "Requiring both crew members to turn the trim wheel simultaneously in a non-normal scenario is extremely undesirable and goes against all philosophies of having one pilot fly and one run the QRH [quick reference handbook: reading out the emergency checklist]. No flight control system should require both pilots to operate it at any stage, let alone in an emergency."

The trade union added: "It is felt that this should be reconsidered (particularly in light of the smaller diameter trim wheel as fitted to the MAX to enable the new larger screens to fit, and as per the scenario observed in the Ethiopian Airlines accident).

ET302 crashed after its pilots, who were fully aware of MCAS after the earlier crash of Lion Air flight 610 (the first 737 Max crash), tried without success to override the flawed software system. MCAS works by automatically trimming the 737 Max's nose downwards if it senses that the aircraft is about to stall, a dangerous condition that normally comes about when the nose is pointing too high and the speed is too low. In ET302's case that MCAS activation was false, however.

Its pilots disabled electric trim motors that had been activated by MCAS and, crash investigators believed, tried to use the manual trim wheel in the cockpit to physically undo what the software had done – following Boeing procedures published after the Lion Air crash. Thanks to the aircraft's excessive speed, built up as MCAS forced its nose to point downwards at the ground, the pilots were unsuccessful. Aerodynamic forces on the control surfaces made it impossible for them to rotate the trim wheel and point the airliner's nose back at the sky.

Meanwhile, back with the FAA's NPRM, the Joint European Max Operators' Group, which includes Ryanair, Norwegian, and Tui, among other airlines, made some minor suggestions for textual edits while reassuring the FAA that they "are not intended to impact on the planned RTS [return to service] programme" for the 737 Max. Some airlines believe all will be well when their Maxes are allowed to fly again. ®

Bootnote

The 737 Max will be known as the 737-7, 737-8 and 737-9. In Ryanair's case it will be known as the 737-8200, a reference to the base -8 Max model having been fettled to fit 200 seats rather than the stock -8's 180ish.

International Air Transport Association aeroplane type codes will be B37M, B38M and B39M should you want to avoid booking a flight on one.


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