737 MAX CRASH
I used to do flight control software for missiles (a really long time ago, and we didn't have to fly for very long ;-)), so I know a little bit about this stuff - here's what I've read about these incidents (the latest crash is still under investigation, so pretty much everything about this one is speculation)
Boeing added MCAS to correct a loss of lift condition, and speculation is that this 'fix' that probably shouldn't happen during take off.
https://phys.org/news/2019-03-ethiopian-airlines-mcas-boeing-max.html
Boeing is releasing an updated autopilot shortly -
Boeing plans autopilot software update after two 737 MAX crashes | ZDNet
That article includes this bit
From the Boeing press release:
A pitch augmentation control law (MCAS) was implemented on the 737 MAX to improve aircraft handling characteristics and decrease pitch-up tendency at elevated angles of attack. It was put through flight testing as part of the certification process prior to the airplane entering service. MCAS does not control the airplane in normal flight; it improves the behavior of the airplane in a non-normal part of the operating envelope.
Boeing's 737 MAX Flight Crew Operations Manual (FCOM) already outlines an existing procedure to safely handle the unlikely event of erroneous data coming from an angle of attack (AOA) sensor. The pilot will always be able to override the flight control law using electric trim or manual trim. In addition, it can be controlled through the use of the existing runaway stabilizer procedure as reinforced in the Operations Manual Bulletin (OMB) issued on Nov. 6, 2018.
There are 3 ways to disable this, per an article I found this morning (and can't find again).
This isn't the same article (the one from this morning showed the locations of the trim control (yoke - left thumb, IIRC) a pitch wheel/crank, and a circuit break, IIRC)
Satcom Guru: 737 MCAS - Failure is an Option
The earlier crash led to Boeing letting pilots know about the MCAS (from
Answers to Your Questions About the Boeing 737 Max 8)
Are all pilots that fly the 737 Max 8 explicitly trained on Boeing’s MCAS flight control system? Do they learn how it works and how to turn it off if it malfunctions?
— Alexandra Zaporozec, Chicago
Before the crash of Lion Air Flight 610 in October, Boeing had not notified pilots that the MCAS was operating on the Max or that in certain circumstances it might cause the airplane to pitch down. After the Lion Air crash, Boeing sent a service bulletin to its customers, and the Federal Aviation Administration followed up with an emergency directive ordering Boeing to change the airplane flight manual and provide the flight crew with a way to avoid being surprised or reacting incorrectly to the MCAS.
I remember flying one of the newer/bigger models (737-800 maybe?) on an early morning flight to Southwest. The landing approach was odd and disturbing (the guy I was with worked on the 737 software a while back, and he gripped the arm rests a couple of times). We said something on the way out and found out that was apparently the second or third commercial flight with that particular airframe, and the first time for that crew, and it behaved a bit different than the -700. They Max8 has more 'bit different' handling, and they added software to protect against one condition, but it may be that they have found a situation where the 'fix' is a really not good thing (esp. if this last crash is the same root cause as the previous).
