737 max 8

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mair

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Unread post13 Mar 2019, 20:14

With the Ethiopian airlines crash in Africa, many airlines have suspended operations on their 737 max fleet. According to a theory that a friend of mine gave, the onboard computers automatically correct any excess angle of attack by overriding pilot control and pitching nose down. Apparently this occurred during the approach phase of flight, and for some reason the pilots were unable to manually override the computer and adjust the pitch attitude. Thereby resulting in the crash.

It’s been asserted that this isn’t the first time the 737 max has had this problem, thus the ban by several airlines. I’m a commercial pilot myself but haven’t flown 737s. My guess is what would have been critical in said scenario would be the altitude at which said angle of attack override occurred.( for those of you familiar with airliners, this mechanism is distinct from the stick shaker that occurs at 1.05 Vs). Thoughts?
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vilters

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Unread post13 Mar 2019, 23:08

Most "high profile" recent crashes (including AF447) are the vicim of failing sensors. (Euh, also including the one and only B-2 crash)

The outside and always exposed sensors are what is killing us.
Be it broken wires, voltage jumps, simpe mechanical or electrical failure, or being taped over during washing and corosion inspections, forgotten to engage anti-ice. You name it, It happened.

it is becoming frightening how many of the latest "crashes" are due to "sensors".
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vilters

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Unread post13 Mar 2019, 23:09

Euh, and for your info, both 737 went down during the take off phase. ( as did the b-2)

And come to think about it? ?
What about a whole test-crew and test airframe and a very unlucky test-pilot who had to eject?

The X-31 crash. Who flew with a new pitot static system and the anti ice was not connected, and nobody bothered to tell the pilot becasue they thought it was not needed for that flight.

Bad luck, they needed it.
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35_aoa

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Unread post14 Mar 2019, 03:01

vilters wrote:Most "high profile" recent crashes (including AF447) are the vicim of failing sensors. (Euh, also including the one and only B-2 crash)

The outside and always exposed sensors are what is killing us.
Be it broken wires, voltage jumps, simpe mechanical or electrical failure, or being taped over during washing and corosion inspections, forgotten to engage anti-ice. You name it, It happened.

it is becoming frightening how many of the latest "crashes" are due to "sensors".


I wouldn't lump AF447 into that category. Yes, there was a momentary AoA vane mismatch (not normally a big deal) due to a short lived presumed icing encounter, but the pilot response was departing the airplane from controlled flight at 37,000 feet, and holding full aft stick all the way until impact, with the FBW version of 0 airspeed the whole way down. The fact that they didn't recognize that is chilling.
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Corsair1963

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Unread post14 Mar 2019, 05:51

Most such accidents end up with a number of factors that lead to the ultimate crash. Even in mechanical cases usually human factors make the situation worse....(i.e. not following the correct procedure)


This is why it's good not to rush to judgment one way or the other. Until we have all of the "facts".
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popcorn

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Unread post14 Mar 2019, 07:09

I just hope that software update coming out end-April fixes the problem.
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mair

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Unread post14 Mar 2019, 07:50

vilters wrote:Most "high profile" recent crashes (including AF447) are the vicim of failing sensors. (Euh, also including the one and only B-2 crash)

The outside and always exposed sensors are what is killing us.
Be it broken wires, voltage jumps, simpe mechanical or electrical failure, or being taped over during washing and corosion inspections, forgotten to engage anti-ice. You name it, It happened.

it is becoming frightening how many of the latest "crashes" are due to "sensors".


Strange, because most airliner aircraft today have multiple sources of inputs to the ADC, with 3-4 pitot tubes and as many static vents. The Air France crash seems to have been caused by a spin since the pilots kept pulling nose up. AF 447 was human error(which unfortunately accounts for 70% of all crashes), because even if the icing over of all pitot probes did occur it wasn’t, by itself a critical condition/assuming of course that there was no ice on any of the control surfaces) . It was made critical by the pilot panic to said situation that ensued.

This particular tragedy seems to have non human causes, thus far .
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rheonomic

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Unread post19 Mar 2019, 01:40

Interesting article with some possibly relevant ASRS reports: https://www.theatlantic.com/notes/2019/ ... ax/584791/

So far I haven't been able to find anything authoritative on the MCAS design. Some news articles I've read seem to indicate that it relies on a single AOA sensor, but I'm not sure how accurate that is. As I understand it there should be an override that does not depend on the MCAS s/w but it seems that this is not in the flight manual and is otherwise poorly documented.
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