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Another deadly 737 Max control bug just found!
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windsmurf:

--- Quote from: sokoloff on June 27, 2019, 01:25:21 pm ---
--- Quote from: EEVblog on June 27, 2019, 12:58:16 pm ---
--- Quote from: ptricks on June 27, 2019, 12:55:58 pm ---Too bad they can't add a toggle switch in the cockpit to cut power from the pin on the micro that controls the specific part the computer is trying to control , something like a auto/manual option.

--- End quote ---
It did/does actually have a switch that disables MCAS, and it could have saved those flights if they had been trained to use it.

--- End quote ---
There's a pair of switches in all 737s that cutout power to the stab trim and all 737 pilots have been trained to use that as a memory item (must be recalled without reference to a printed checklist) in the event of stab trim runaway.

--- End quote ---

They modified the switch functionality with the 737 max.

https://www.seattletimes.com/business/boeing-aerospace/boeing-altered-key-switches-in-737-max-cockpit-limiting-ability-to-shut-off-mcas/
MrMobodies:

--- Quote ---But on the Ethiopian Airlines flight, the pilots appear to have recognized the errant MCAS problem and flipped the cutoff switches as descrbed in the checklist. But then it appears that the pilots were unable to move the manual wheel, likely because the forces on the tail made it physically challenging to turn.

After failing to manually control the stabilizer, the Ethiopian Airlines pilots appear to have flipped the cutoff switches back on, which awakened the MCAS system. It soon sent the plane diving to Earth.

Lemme said he’s surprised that Boeing made the change to take away the functionality that could have allowed the pilots to shut off MCAS without shutting off the electric switches at their thumbs.

--- End quote ---

So turn off the cutout switches and it cuts out the controls turn it back on and the MCAS overrides the pilots control and controls the plane based on some faulty sensor.


https://en.wikipedia.org/wiki/Maneuvering_Characteristics_Augmentation_System

--- Quote ---Boeing and the FAA decided that the AOA display and an AOA disagree light, which signals if the sensors give different readings, were not critical features for safe operation.[42] Boeing charged extra for the addition of the AoA indicator to the primary display.[43][44]. In November 2017, Boeing engineers discovered that the standard AoA disagree light cannot independently function without the optional AoA indicator software, affecting 80% of the global fleet which had not ordered the option.[45][46][47] The software remedy was scheduled to coincide with the roll out of the elongated 737 MAX 10 in 2020, only to be accelerated by the Lion Air accident. Furthermore, the problem had not been disclosed to the FAA until 13 months after the fact. Although it is unclear whether the indicator could have changed the outcome for the ill fated flights, American Airlines said the disagree indicator provided the assurance in continued operations of the airplane. "As it turned out, that wasn't true." [48]

Boeing CEO Dennis Muilenburg has stated that there was "no surprise, or gap, or unknown here or something that somehow slipped through a certification process."[49] On April 29, 2019 he stated the design of the aircraft was not flawed and reiterated that it was designed per Boeing's standards.[50] In a May 29 interview with CBS, Boeing admitted that it had botched the software implementation and lamented the poor communications. [51]
--- End quote ---

It looks like some things were also missing and the airlines wanted save money.
Gyro:
I knew this would happen as soon as a second thread started - go and look at the original thread, there is a lot of relevant information already covered there, I suggest starting at the last page and working backwards!

 https://www.eevblog.com/forum/chat/lion-air-crash-jakarta-boeing-737-had-prior-instrument-error/1075/


--- Quote from: MrMobodies on June 27, 2019, 08:54:27 pm ---It looks like some things were also missing and the airlines wanted save money.

--- End quote ---

Irrc, that AOA disagree indicator was a $80k per plane option and Boeing couldn't make it work.
MrMobodies:

--- Quote from: Gyro on June 27, 2019, 09:17:59 pm ---I knew this would happen as soon as a second thread started - go and look at the original thread, there is a lot of relevant information already covered there, I suggest starting at the last page and working backwards!

Irrc, that AOA disagree indicator was a $80k per plane option and Boeing couldn't make it work.

--- End quote ---


Sorry about that. I forgot all about the thread.

Lot of money for something they couldn't get working.
SiliconWizard:
That doesn't bode well for Boeing. ::)
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