prashanth.mundkur@gmail.com
Date: Tue, 5 Feb 2019 08:33:27 -0800
Behind the Lion Air Crash, a Trail of Decisions Kept Pilots in the Dark
By James Glanz, Julie Creswell, Thomas Kaplan and Zach Wichter
Feb. 3, 2019
https://www.nytimes.com/2019/02/03/world/asia/lion-air-plane-crash-pilots.html
In designing the 737 Max, Boeing decided to feed MCAS with data from
only one of the two angle of attack sensors at a time, depending on which
of two, redundant flight control computers -- one on the captain's side,
one on the first officer's side -- happened to be active on that flight.
That decision kept the system simpler, but also left it vulnerable to a
single malfunctioning sensor, or data improperly transferred from it -- as
appeared to occur on the day of the crash.
There is no evidence that Boeing did flight-testing of MCAS with erroneous
sensor data, and it is not clear whether the F.A.A. did so. European
regulators flight-tested the new version of the plane with normal sensor
data feeding into MCAS but not with bad data, the pilot familiar with the
European certification process said. [...]
Older 737s had another way of addressing certain problems with the
stabilizers: Pulling back on the yoke, or control column, one of which
sits immediately in front of both the captain and the first officer, would
cut off electronic control of the stabilizers, allowing the pilots to
control them manually.
That feature was disabled on the Max when MCAS was activated -- another
change that pilots were unlikely to have been aware of. After the crash,
Boeing told airlines that when MCAS is activated, as it appeared to have
been on the Lion Air flight, pulling back on the control column will not
stop so-called stabilizer runaway.
There's a lot more context in the full article.