Boeing Built Deadly Assumptions into 737 Max, Blind to a Late Design Change
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Re: Boeing Built Deadly Assumptions into 737 Max, Blind to a Late Design Change
#2Is this only me, or all this one-vs-two AoA sensor talk seems some kind of diversion from the real problem with this plane.
I mean, if one-sensor based MCAS failed twice so early in the life span of the plane model, what is the probability that a two-sensor model will fail pretty soon as well? The math should be simple, we have all data needed: combined hours flown by all planes of the type and number of failures (at least two known, which can help us to estimate a MTBF of the sensor).
Re: Boeing Built Deadly Assumptions into 737 Max, Blind to a Late Design Change
#3Is this only me, or all this one-vs-two AoA sensor talk seems some kind of diversion from the real problem with this plane. I mean, if one-sensor based MCAS failed twice so early in the life span of the plane model, what is the probability that a two-sensor model will fail pretty soon as well? The math should be simple, we have all data needed: combined hours flown by all planes of the type and number of failures (at…
The AOA sensors are effectively a consumable, and would undergo regular replacement over the life of the aircraft, the odds of BOTH of them failing at the same moment in the same flight is very very small.
Re: Boeing Built Deadly Assumptions into 737 Max, Blind to a Late Design Change
#4Is this only me, or all this one-vs-two AoA sensor talk seems some kind of diversion from the real problem with this plane. I mean, if one-sensor based MCAS failed twice so early in the life span of the plane model, what is the probability that a two-sensor model will fail pretty soon as well? The math should be simple, we have all data needed: combined hours flown by all planes of the type and number of failures (at…
The problem isn’t failure, but detecting failure.
If the sensor had just stopped responding, there wouldn’t have been any problem. The planes would keep flying, the sensors would get replaced, and everyone would be fine.
What happened was that the sensor gave erroneous readings. The MCAS system reacted to those erroneous reading and crashes the plane.
With two sensors, you can detect failure. It’s very unlikely that both would fail simultaneously. If they did, it’s very unlikely that both would provide the same erroneous readings.
Re: Boeing Built Deadly Assumptions into 737 Max, Blind to a Late Design Change
#5Is this only me, or all this one-vs-two AoA sensor talk seems some kind of diversion from the real problem with this plane. I mean, if one-sensor based MCAS failed twice so early in the life span of the plane model, what is the probability that a two-sensor model will fail pretty soon as well? The math should be simple, we have all data needed: combined hours flown by all planes of the type and number of failures (at…
The problem isn’t failure, but detecting failure. If the sensor had just stopped responding, there wouldn’t have been any problem. The planes would keep flying, the sensors would get replaced, and everyone would be fine. What happened was that the sensor gave erroneous readings. The MCAS system reacted to those erroneous reading and crashes the plane. With two sensors, you can detect failure. It’s very unlikely that…
It is not unlikely, I don't remember details, but I remember the case when two broken sensors voted over working sensor.
The problem is that in order to save tiny amount of money Boing made plane rely on unreliable sensors.
Re: Boeing Built Deadly Assumptions into 737 Max, Blind to a Late Design Change
#6“After Boeing removed one of the sensors from an automated flight system on its 737 Max, the jet’s designers and regulators still proceeded as if there would be two.”
No, no, no. This is just more of shifting the blame from Boeing upper management. They couldn't use two Angle of Attack (AOA) sensors as when there was a differing reading there would be no way to know the correct reading, which is why MCAS used a single AOA sensor on the right-hand side.
Re: Boeing Built Deadly Assumptions into 737 Max, Blind to a Late Design Change
#7Is this only me, or all this one-vs-two AoA sensor talk seems some kind of diversion from the real problem with this plane. I mean, if one-sensor based MCAS failed twice so early in the life span of the plane model, what is the probability that a two-sensor model will fail pretty soon as well? The math should be simple, we have all data needed: combined hours flown by all planes of the type and number of failures (at…
> what is the probability that a two-sensor model will fail pretty soon as well
It's actually higher than the probability that a one-sensor version will fail. With two sensors, you have an effective failure if either sensor fails, and the probability of that happening is roughly twice the probability that a single sensor will fail (assuming failures are independent, which is not necessarily a valid assumption).
However, with two sensors you can tell when one has failed (even though you may not know which one it was) and so the consequences of the failure might be less severe.
The problem is: now pilots need to be prepared to fly the plane with a failure sensor, which is to say, without MCAS. To do that, they will need additional training. Avoiding that was the whole point of MCAS in the first place. That's the reason it's taking so long to sort this out. Technically, it's an easy problem to solve. It's the economics that are daunting.
Re: Boeing Built Deadly Assumptions into 737 Max, Blind to a Late Design Change
#8Earlier quoted context omitted.
The problem isn’t failure, but detecting failure. If the sensor had just stopped responding, there wouldn’t have been any problem. The planes would keep flying, the sensors would get replaced, and everyone would be fine. What happened was that the sensor gave erroneous readings. The MCAS system reacted to those erroneous reading and crashes the plane. With two sensors, you can detect failure. It’s very unlikely that…
It is not unlikely, I don't remember details, but I remember the case when two broken sensors voted over working sensor. The problem is that in order to save tiny amount of money Boing made plane rely on unreliable sensors.
Assuming that’s true, the fact that it has happened before does not mean simultaneous failure is not incredibly unlikely. Unlikely things do happen. One might call it extraordinarily bad luck.
Re: Boeing Built Deadly Assumptions into 737 Max, Blind to a Late Design Change
#9Earlier quoted context omitted.
The problem isn’t failure, but detecting failure. If the sensor had just stopped responding, there wouldn’t have been any problem. The planes would keep flying, the sensors would get replaced, and everyone would be fine. What happened was that the sensor gave erroneous readings. The MCAS system reacted to those erroneous reading and crashes the plane. With two sensors, you can detect failure. It’s very unlikely that…
It is not unlikely, I don't remember details, but I remember the case when two broken sensors voted over working sensor. The problem is that in order to save tiny amount of money Boing made plane rely on unreliable sensors.
It’s not unlikely... because of some vague memory you have?
Re: Boeing Built Deadly Assumptions into 737 Max, Blind to a Late Design Change
#10Is this only me, or all this one-vs-two AoA sensor talk seems some kind of diversion from the real problem with this plane. I mean, if one-sensor based MCAS failed twice so early in the life span of the plane model, what is the probability that a two-sensor model will fail pretty soon as well? The math should be simple, we have all data needed: combined hours flown by all planes of the type and number of failures (at…
The problem isn’t failure, but detecting failure. If the sensor had just stopped responding, there wouldn’t have been any problem. The planes would keep flying, the sensors would get replaced, and everyone would be fine. What happened was that the sensor gave erroneous readings. The MCAS system reacted to those erroneous reading and crashes the plane. With two sensors, you can detect failure. It’s very unlikely that…
> With two sensors, you can detect failure
You get a reading of 20 on one sensor and get a reading of 34 on the second, which one is correct. To achieve reliability a minimum of five sensors need be used. four primary and one back-up. If three primary agree then system normal. If two primary disagree then switch to backup.