Primarily for general aviation discussion, but other aviation topics are also welcome.
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#1822694
A4 Pacific wrote:I already have friends asking how they can avoid flying on it!

The way the market due Covid seems to be going there might be thousands of perfectly good aeroplanes being scrapped. It will take a brave airline that tries to attract pax to a notorious airframe, regardless of finance agreements / leases.
#1827102
Stu B wrote:
There is a misconception as illustrated by some comments above that the MCAS is designed to operate routinely. This is not the case ,

True - but that in turn assumes that the on-board sensors correctly identify WHETHER the aircraft is operating routinely. The latest build-quality allegations suggest perhaps the sensors cannot always be trusted to be doing that!


Yes , however I wasn’t commenting on the problems and malfunctions , just on when it was designed to operate. It was/is only designed to operate in a specific regime of abnormal flight.

Having just flown the sim and looked at the operation of the system & the fail safes put in place , I am confident in it. It’s also a lovely aeroplane to fly, nicer handling than the NG . Just need to convince the passengers , that’ll be a steep climb. As already alluded to , it’ll come down to cost of tickets for most.
#1827113
While ever MCAS has only two inputs for AoA and dynamic info, it will always be flawed. If they can give it 3 inputs like all FBW does, so a voting system can be used, it will be safe....... Until then, I am not sure.
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#1827155
As I wrote above, a voting system does not require three inputs to indicate a problem. A 2oo3 vote is required for fault-tolerance, i.e., the system continues to fulfil its designated safety function in the presence of a single fault (1). However, a 1oo2 vote with two sensor inputs is sufficient to detect a fault in the system (the sensors disagree) and thus declare the safety system inoperable. The aircraft will still fly perfectly without MCAS enabled.

(1) Technically, for asynchronous inputs such as an analogue AoA indicator, it’s actually a 4-way Byzantine vote that is required to resolve a fault in the presence of asynchronous inputs presented to the three triple mode redundant lanes.

Iceman 8)
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#1827194
Which I guess was the main focus of their changes because in the original system, a single failure was creating incorrect pitch downs, whereas it should have disabled the system with a Master Caution perhaps ?
#1827201
Yes, that was there major flaw. Believe in one AoA sensor and when that goes faulty, indicating an unsafe AoA, believe it, MCAS then does what it’s supposed to and catastrophe ensues. With just a single sensor, there is no means of determining if the data it is giving is correct.

Iceman 8)
#1827207
Have they also not made it possible for easier, one-handed operation of the manual trimmer. Replacing the 'two people and all their best efforts couldn't overcome it' system?

Rob P
#1827230
Iceman wrote:... Believe in one AoA sensor and when that goes faulty, indicating an unsafe AoA, believe it, MCAS then does what it’s supposed to and catastrophe ensues. With just a single sensor, there is no means of determining if the data it is giving is correct.

Iceman 8)


ISTR reading that all Max's were equipped with 2 AoA sensors, but by default the output of only 1 was fed to MCAS. Airlines could specify that both should be fed, and that discrepancies could both warn the crew and disable MCAS, and that this was merely a software change; but

a. this would have cost the airline, and

b. it would also have required training the crew about the very existence of MCAS, the role of MCAS, and action to be taken in event of a discrepancy warning. As the major selling point by Boeing to the airline customers of the Max was that 737 Type-Rated crew would need no extra training, this option was either not explained or not pushed to the airline customers' purchasing decisionmakers.

Happy to be corrected, of course.
#1827235
Quite possibly @kanga, although for both the reasons you mention, I guess that it wasn’t pushed as a feature and there was no uptake as a consequence. The facts that this shouldn’t have been a costed option and that the requirement for difference training shouldn’t have been brushed under the carpet are perhaps the real issues.

Iceman 8)
Trent772, kanga, Stu B and 1 others liked this
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