The Ethiopian Airlines 737 Max 8 that crashed this month, killing all 157 passengers and crew, was actively using Boeing's Maneuvering Characteristics Augmentation System (MCAS) that is thought to have brought down a similar 737 five months earlier.
In an interview with the Wall Street Journal over the weekend, Ethiopian CEO Tewolde Gebremariam said the MCAS anti-stalling system was, “to the best of our knowledge,” active as the aircraft crashed on March 10. The plane's black box recorder has been recovered, analyzed in France, and its contents shared with investigators in the US, EU, and other nations.
The MCAS software was introduced with the 737 Max range of aircraft to deal with design changes to the airframe. Boeing put larger, more fuel-efficient engines on the Max range, which had to be mounted forward of the wing, which made the aircraft more prone to tipping back and stalling during flight. If the MCAS software detects the aircraft is rising too steeply, it automatically moves the stabilizers at the back of the aircraft to bring the nose back down.
It's thought an angle-of-attack sensor on-board Lion Air flight 610 in October sent faulty signals to MCAS, leading the system to activate and pitch the 737 Max 8 aircraft nose down, and repeatedly restarting such moves after the pilots tried to override it. It eventually crashed into the sea, killing all 189 passengers and crew.
Read the manual – oh wait!
It is possible to disable MCAS. Indeed, a day before the Lion Air 610 tragedy, an off-duty pilot hitching a ride on another Lion Air 737 Max 8 flight realized the plane was dangerously pitching down due to the MCAS activating, and instructed the on-duty pilots on how to disable the safety system so they could regain control of the aircraft, saving all on-board. Disabling MCAS involved flipping the right switches to kill it before it killed them. Relatively few pilots were aware of MCAS, though: it wasn't mentioned in the basic 737 Max pilot's manuals.
Bear in mind, aviators have just seconds to override MCAS to avoid an unrecoverable nose dive, according to simulations.
The aircraft's designers did come up with a warning indicator to alert pilots if there is an error in the angle-of-attack sensor data feeding into MCAS, a condition that would lead to the safety system making lethal decisions. But this warning indicator doesn't come as standard, and many airlines, particularly at the cheaper end of the market, didn't order them. Boeing has now said the $80,000 upgrade will be installed as standard on all new 737 Maxes.
The saga has raised other questions, too. Boeing's hometown newspaper, The Seattle Times, has published a series of reports highlighting purported failures in the 737 Max's design and certification.
If the claims are correct, America's Federal Aviation Authority (FAA) took a rather hands-off approach to checking out the new design, and outsourced much of the work to Boeing to certify its own kit. This led to a miscommunication, with the watchdog believing MCAS could, at most, angle the plane downwards by 0.6 degrees, whereas the actual figure is 2.5 – enough to avoid stalling the thing.
Boeing is now working on a fix for the issue, including: getting data from multiple sensors to check that the angle-of-attack reading is correct before activating MCAS; making it easier to disable the system and to stop it resetting; and providing details of its operation in the pilot's training materials. The updated software will be reportedly pushed out to airlines for free, though it needs to be signed off by the FAA.
"Safety is our highest priority as we design, build and support our airplanes," Boeing said last week in a statement.
"While investigators continue to work to establish definitive conclusions, Boeing is finalizing its development of a previously-announced software update and pilot training revision that will address the MCAS flight control law's behavior in response to erroneous sensor inputs."
It can't come soon enough for the largest passenger airline in the world, American Airlines.
The biz has had a long-standing good relationship with Boeing, and was an enthusiastic adopter of the 737 Max line. But it was hit hard when the FAA decided (belatedly) to ground all of the suspect 737 Maxes for the moment. On Sunday, American announced large-scale cancellations as it has run out of aircraft to fill in the gaps caused by the grounding order.
"In an effort to provide more certainty and avoid last minute flight disruptions, American has extended cancellations through April 24," the airline said in a statement.
Boeing big cheese repeats pledge of 737 Max software updates following fatal crashesREAD MORE
"This will result in the cancellation of approximately 90 flights each day based on our April schedule. By proactively canceling these flights, we are able to provide better service to our customers with availability and rebooking options."
Folks who are on cancelled flights will be told in advance by the airline so that they can make alternative arrangements. But it's still going to mean a lot of peeved passengers, profitable routes under-served, and adds to Boeing's woes.
Even if the FAA makes a quick order to lift the grounding and ease American's woes, the same might not be true for Boeing's aircraft in Europe. On Sunday, a senior EU official told the Financial Times the 737 Max family won't fly on the continent until Euro nations' safety inspections have checked for themselves that the aircraft are safe.
“The system was based on trust, and the trust has gone,” the official said. ®