> Original MCAS system used only 1 AOA sensor and switched back and forth between the two after every flight.
Who the fuck thought that was a good idea???
Let's make it 10x more difficult to detect that there is a problem.
Who the fuck thought that was a good idea???
Let's make it 10x more difficult to detect that there is a problem.
If you're looking from a regulatory compliance PoV towards optimising sales - that's actually desired behaviour - if it's overly complex to diagnose it's less likely that somebody understands and point fingers back at us. You know, basically what happened after the Lion Air crash - Boeing being all over "it's not us, it's them"
I'm not a pilot, but if the controls are linked -- why would the plane need to know where the pilot is sitting (or even have a switch for it)?
(Any 747 pilots reading? Can you please fill in the gaps for me?)
I said 747 because I was thinking Boeing at the time, and that was the first of their aircraft I could think of!
I was also thinking something smaller like a Cessna might not have the same setup because they're used for very different things (the air travel equivalent of a bus vs. a car).
That's what I meant yes
Independent comparable sensor input is invaluable and irreplaceable.
To be fair the statistics are swayed slightly by a number of factors, training accidents and different risk profiles of the flights.
As outlined above, you double the probability that a mechanical problem occurs. (For p small, 1-(1-p)^2 is around 2p).
Now, if the pilots are very much on top of things (well trained and current), then they can control things and safely land at the nearest suitable airport. However, if they make a mistake (and that's surprisingly easy [1]), it could easily be fatal.
A single-engine plane with an engine failure, in contrast, becomes a bad glider, with a decent chance of surviving the ensuing forced landing.
[1] For example, the TransAsia ATR 72 twin turbo prop clipping a bridge in Taiwan after the crew erroneously shut down the "good" engine.
The only reason I know is because the captain informed us about it and added that since it was technically an emergency landing we would be greeted by the fire department.
He then turned the plane around and landed as if nothing had happened.
The bloke across the corridor, an old pilot, complained about how there never happened anything remotely exiting on any of his flights ;-)
[0]: to be as accurate as possible I think what he said was they'd lost oil pressure on one engine and decided to shut it down voluntarily.
When one engine fails, while you've lost 50% horsepower, you've lost more like 90% of excess horsepower which is what you need to accelerate and to climb. And assymmetric thrust is dangerous at slow airspeed. You must react exactly correctly and quickly. Failure on takeoff roll means an immediate abort. Failure at takeoff with runway remaining means cutting power and landing on what remains. Failure once airborne and you must quickly identify the failed engine, apply full opposite rudder (toward the good engine), if you don't do this while in a full power low airspeed climb the airplane will absolutely roll over. Many accidents are the result of continuing when they should have aborted, and being anemic or slow with corrective rudder.
Turbine powered airplanes are way different, they have a lot more excess thrust available so powerplant failure is not dire. They have so much more power that they will still easily accelerate to a safe single engine takeoff speed and climb away for a circle to land, which is safer than aborting after certain speeds that smaller twins won't get to on takeoff. That's all part of the computation for "balanced field length".
Later, the MCAS ended up adjusting the trim multiple times, by an amount the pilots couldn't override with the stick. Thus it should have been safety level DAL-A (loss of plane) [3] - but the safety analysis and MCAS design weren't updated to reflect that.
And the FAA, in what with hindsight seems like a ridiculously naive move, allowed Boeing to self-certify their own faulty safety analysis.
[1] https://www.seattletimes.com/business/boeing-aerospace/faile... [2] https://news.ycombinator.com/item?id=19419454 [3] https://en.wikipedia.org/wiki/DO-178B#Software_level
A problem no one can detect is a problem you don't need to fix ! /s