Moon of Alabama
provides a good summary of what is now believed to be the reason Boeing's 737MAX airliner is crash prone.
Four factors seem to be responsible.
Suboptimal design:
| In 2010 Airbus decided to offer its A-320 with a New Engine Option (NEO) which uses less fuel. To counter the Airbus move Boeing had to follow up. The 737 would also get new engines for a more efficient flight and longer range. The new engines on the 737 MAX are bigger and needed to be placed a bit different than on the older version. That again changed the flight characteristics of the plane by giving it a nose up attitude. |
The plane is low slung for easy access to the baggage hold, but with larger engine nacelles it was necessary to raise the top of the nacelles above the leading edge of the wing, thereby creating additional lift. Thus, whereas, in most aircraft, if the pilot takes his hand off the stick, the plane will continue in level flight, the 737MAX is inherently unstable and tends to go nose up, leading to a stall.
Deceptive marketing:
The new flight characteristic of the 737 MAX would have require a retraining of the pilots. But Boeing's marketing people had told their customers all along that the 737 MAX would not require extensive new training. Instead of expensive simulator training for the new type, experienced 737 pilots would only have to read some documentation about the changes between the old and the new versions.
To make that viable, Boeing's engineers used a little trick. They added a "maneuver characteristics augmentation system" (MCAS) that pitches the nose of the plane down if a sensor detects a too high angle of attack that might lead to a stall. That made the flight characteristic of the new 737 version similar to the old one. |
By calling the automated anti-stall system (ASS) the "Maneuver Characteristics Augmentation System" (MCAS) deliberately or otherwise deflected attention from the vital importance of that system.
A poorly designed engineering solution to the plane's inherent instability:
The 737 MAX has two flight control computers. Each is connected to only one of the two angle of attack sensors. During a flight only one of two computer runs the MCAS control. If it detects a too high angle of attack it trims the horizontal stabilizer down for some 10 seconds. It then waits for 5 seconds and reads the sensor again. If the sensor continues to show a too high angle of attack it again trims the stabilizer to pitch the plane's nose done.
MCSA is independent of the autopilot. It is even active in manual flight. There is a procedure to deactivate it but it takes some time.
One of the angle of attack sensors on the Indonesian flight was faulty. Unfortunately it was the one connected to the computer that ran the MCAS on that flight. Shortly after take off the sensor signaled a too high angle of attack even as the plane was flying in a normal climb. The MCAS engaged and put the planes nose down. The pilots reacted by disabling the autopilot and pulling the control stick back. The MCAS engaged again pitching the plane further down. The pilots again pulled the stick. This happened some 12 times in a row before the plane crashed into the sea.
To implement a security relevant automatism that depends on only one sensor is extremely bad design. To have a flight control automatism engaged even when the pilot flies manually is also a bad choice. But the real criminality was that Boeing hid the feature. |
Concealment of a Fundamental System Vulnerability:
With seeming insanity, Boeing failed to inform pilots of how the "solution" to the plane's tendency to stall worked, or might fail to work, or if necessary, might be shut off to allow the aircraft to be flown manually:
| Neither the airlines that bought the planes nor the pilots who flew it were told about MCAS. They did not know that it exists. They were not aware of an automatic system that controlled the stabilizer even when the autopilot was off. They had no idea how it could be deactivated. |
Boeing's best way forward would appear to be the resignation of the entire board of directors and their replacement by responsible people with relevant qualifications. Likewise, the top guys at the Federal Aviation Administration which was responsible for giving the plane a certificate of airworthiness should, but won't, go now.
Related:
CanSpeccy:Way to Go: Foundering Boeing Corp. Replaces Aeronautical Engineer With Real Estate Developer as CEO
FAA’s close ties to Boeing questioned after 2 deadly crashesPiece Found At Ethiopian Airlines Crash Site Shows Jet Was Set To DiveNew Satellite Network Offers Clues Into Boeing 737 Max CrashesSomething was extraordinarily wrong: Doomed Boing Swung Up and Down Hundreds of Feet
