Lack of redundancies on Boeing 737 MAX baffles some involved in developing it
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Re: Lack of redundancies on Boeing 737 MAX baffles some involved in developing it
#2Despite the headline, the article ends with:
That triple-sensor system isn’t foolproof, however.
In 2008, on a customer-acceptance flight of an Airbus A320, two of the angle-of-attack sensors froze and those two sensors then outvoted the third. When the pilots went to demonstrate the stall-prevention system, they were not aware of the malfunctioning sensors. The plane crashed, killing the seven people on board.
The same problem arose again on a 2014 Airbus A321 Lufthansa flight leaving Spain. Eight minutes after takeoff, two of the angle-of-attack sensors froze at the same pitch. This time, after a drop in altitude, the pilots were able to regain control and complete the flight.
Any automation system can fail, and when that happens, hope that through some combination of luck, skill, experience, and training, the pilot will get the plane safely to the destination.
Re: Lack of redundancies on Boeing 737 MAX baffles some involved in developing it
#3Despite the headline, the article ends with: That triple-sensor system isn’t foolproof, however. In 2008, on a customer-acceptance flight of an Airbus A320, two of the angle-of-attack sensors froze and those two sensors then outvoted the third. When the pilots went to demonstrate the stall-prevention system, they were not aware of the malfunctioning sensors. The plane crashed, killing the seven people on board. The s…
They need triple temperature sensors on those sensors to sense when they freeze...
Re: Lack of redundancies on Boeing 737 MAX baffles some involved in developing it
#4Despite the headline, the article ends with: That triple-sensor system isn’t foolproof, however. In 2008, on a customer-acceptance flight of an Airbus A320, two of the angle-of-attack sensors froze and those two sensors then outvoted the third. When the pilots went to demonstrate the stall-prevention system, they were not aware of the malfunctioning sensors. The plane crashed, killing the seven people on board. The s…
It does seem like a primitive system to use the wind for AoA, seems like there should be better and more reliable ways to determine it.
Update: AoA not AoT
Re: Lack of redundancies on Boeing 737 MAX baffles some involved in developing it
#5Despite the headline, the article ends with: That triple-sensor system isn’t foolproof, however. In 2008, on a customer-acceptance flight of an Airbus A320, two of the angle-of-attack sensors froze and those two sensors then outvoted the third. When the pilots went to demonstrate the stall-prevention system, they were not aware of the malfunctioning sensors. The plane crashed, killing the seven people on board. The s…
They need triple temperature sensors on those sensors to sense when they freeze...
you're hired!
Re: Lack of redundancies on Boeing 737 MAX baffles some involved in developing it
#6Despite the headline, the article ends with: That triple-sensor system isn’t foolproof, however. In 2008, on a customer-acceptance flight of an Airbus A320, two of the angle-of-attack sensors froze and those two sensors then outvoted the third. When the pilots went to demonstrate the stall-prevention system, they were not aware of the malfunctioning sensors. The plane crashed, killing the seven people on board. The s…
It does seem like a primitive system to use the wind for AoA, seems like there should be better and more reliable ways to determine it. Update: AoA not AoT
That's what AoA is though. It's the relative wind angle over the wing. The wind matters. You can't calculate AoA simply from pitch or vertical speed or something like that.
Re: Lack of redundancies on Boeing 737 MAX baffles some involved in developing it
#7Despite the headline, the article ends with: That triple-sensor system isn’t foolproof, however. In 2008, on a customer-acceptance flight of an Airbus A320, two of the angle-of-attack sensors froze and those two sensors then outvoted the third. When the pilots went to demonstrate the stall-prevention system, they were not aware of the malfunctioning sensors. The plane crashed, killing the seven people on board. The s…
I've had to do a bit of functional safety stuff recently and one of the things they focus on are "common cause failures" (of which this is a perfect example - if one of the sensors freezes, the others are likely to do so as well). If you want to be sure something works, it's not enough to just have two or three copies of the same system. You have to have redundancy in manner of operation as well.
Re: Lack of redundancies on Boeing 737 MAX baffles some involved in developing it
#8Despite the headline, the article ends with: That triple-sensor system isn’t foolproof, however. In 2008, on a customer-acceptance flight of an Airbus A320, two of the angle-of-attack sensors froze and those two sensors then outvoted the third. When the pilots went to demonstrate the stall-prevention system, they were not aware of the malfunctioning sensors. The plane crashed, killing the seven people on board. The s…
If there are three of the same type (make/model?) of sensor teaming to vote on the status being measured I'm not suprised that they can suffer the same failure (iceing) at the same time causing an incorrect state to be upvoted.
I would have thought that for any condition there would be more than one mechanism available to sense it. You could get different devices to vote on what is the real condition.
This has been done for years in visual cockpits with regards to an artifical horizon. The pilot only has to look out the window (assuming visibliity) to confirm what the instrument is reporting. Of course when the pilot loses visibility and starts to rely on their inner ear for "level" bad things can happen.
Many more simple planes, especially things like gliders, have a simple ball bearing in a curved tube to indicate "down" as well as the more convential artifical horizon.
Re: Lack of redundancies on Boeing 737 MAX baffles some involved in developing it
#9Re: Lack of redundancies on Boeing 737 MAX baffles some involved in developing it
#10Despite the headline, the article ends with: That triple-sensor system isn’t foolproof, however. In 2008, on a customer-acceptance flight of an Airbus A320, two of the angle-of-attack sensors froze and those two sensors then outvoted the third. When the pilots went to demonstrate the stall-prevention system, they were not aware of the malfunctioning sensors. The plane crashed, killing the seven people on board. The s…
Triple-redundancy isn't 100% foolproof, but it is a lot better than two potentially-faulty sensors.
I know this isn't a great example, but triple redundancy is enough of a design cornerstone that Arthur C. Clarke made it one of the defining features of Rendezvous With Rama, a classic sci-fi story about an Oumuamua-like object that people manage to land on:
>It was now strikingly apparent that the "city", like so much of Rama, was triplicated. It consisted of three identical, circular complexes or superstructures, rising from a long, oval foundation. Photographs taken from the hub had also indicated that each complex was itself divided into three equal components, like a pie sliced into 120-degree portions. This would greatly simplify the task of exploration; presumably they had to examine only one-ninth of [the city] to see the whole of it.
It doesn't exactly sound like a new or controversial idea, you know?