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What's not clear from the article is how likely this failure mode actually is to occur, even if the pilots happen to forget to disable the anti-ice. The fact t
by avalys 3y ago
What's not clear from the article is how likely this failure mode actually is to occur, even if the pilots happen to forget to disable the anti-ice.
The fact that this issue is present in the existing 737 Max variants, and none appear to have actually experienced a structural failure, suggests the probability is low.
It is easy for a bunch of keyboard warriors here on HN to insist that only zero risk is acceptable. In the real world, everything is a continuum and without knowing quantifiably where on the risk continuum this issue is, any discussion is meaningless.
- troupo 3y agoIn a large enough dataset any edge case will occur with 100% certainty. There are ~100 000 flights per day worldwide. I'd say the conditions described occur all the time
- avalys 3y agoThis is also a trivially true statement and meaningless for real-world decision-making. In a large enough dataset and given enough time, a meteor will eventually hit a plane in-flight and destroy it. Should regulation require the airplanes carry anti-meteor armor? Your qualitative judgement that these conditions described occur all the time actually suggests it's not a big deal, because the currently-flying Max 8 and Max 9 variants have the same issue, and none have experienced a structural failure. The scenario here is that, if the pilots forget to turn off anti-ice, the nacelle will eventually overheat, weaken, and possibly fail. But clearly that is not guaranteed to happen, or happen immediately. What I'm saying is that actual decision-making here depends on what the statistics of this possible failure actually are, given that the pilots forget to turn off the anti-ice.
- pi-e-sigma 3y agoYour analogy doesn't make sense because there is no feasible way to protect a plane from a meteor hit (if it ever happens). So it's either take your chances or don't fly at all. The failure mode we are discussing absolutely can be prevented, it's just a matter of some extra cost.
- troupo 3y agoThere are degrees of possibilities nd confidence intervas and... You can start with statistics of icing/de-icing a plane vs. statistics of meteors hitting a plane.
- StreetChief 3y agowait so, because similar planes have not had failures yet, i should accept risk of death for airline profitability?
- avalys 3y agoYou are already accepting a risk of death for airline profitability. These tradeoffs are made all the time.
- StreetChief 3y agoTo me, variant 7 is different than 8 and 9, and 7 should not be given special treatment because of its similarity to the others. Any discussion is meaningless?
- wolverine876 3y ago> none appear to have actually experienced a structural failure, suggests the probability is low. Low probabilty is much too high for this domain, of course. The question is, how low? In airplane design, almost all catastrophic failures happen only the first time.
- MaxBarraclough 3y ago> In airplane design, almost all catastrophic failures happen only the first time. Presumably you meant airliners specifically?
- wolverine876 3y agoWithout knowing the specific technical meaning of 'airliners', yes that sounds about right. Maybe 'non-experimental airplanes'?
- marcosdumay 3y agoGeneral aviation is full of repeating disasters. And agricultural aviation is well, about as safe as a bunch of cowboys operating tractors.
- wolverine876 3y agoRepeating catastrophic design flaws though? I'd think the even the most inhumane manufacturers would face too much liability to allow the second one to happen.
- MaxBarraclough 3y agoWhat counts as a catastrophic design flaw? Piston engines sometimes stop unexpectedly. This happens in general aviation, and sadly it quite often results in a fatal crash. If you ban piston engines and only allow turbine engines (which are much less prone to unexpectedly stopping), you effectively kill general aviation.
- lamontcg 3y ago> The fact that this issue is present in the existing 737 Max variants, and none appear to have actually experienced a structural failure, suggests the probability is low. The fact that the space shuttle flew 60 times without SRB o-rings being a problem suggests that the probability of their failure was also low.
- Lanzaa 3y agoAs per the petition from Boeing: > "it cannot be shown that the EAI [Engine Anti-Ice] system meets the probability requirements applicable to this regulation." In my understanding, Boeing is asking for to be excluded from the risk assessment entirely. They know there is a possibility that the structure could be weakened enough to fail during normal flight. > "the nacelle inlet structural temperatures during EAI operation may cause the inner barrel to lose sufficient strength such that capability to carry limit and ultimate loads may not be maintained." > "analysis and engineering flight testing showed there is a potential for structural damage." Their entire justification for why the risk is acceptable is that no one has had parts fly off yet and surely pilots will follow the flight rules to turn off the deicer: > "737 MAX has been in service since 2017 and has accumulated over 6.5 million flight hours. In that time, there have been no reported cases of parts departing aircraft (PDA) due to overheating of the engine nacelle inlet structure". > "Operators [Pilots] must adhere to the mandatory AD [Airworthiness Directive], mitigating the potentially unsafe condition." Oh, and they petition relief from some of the human factors requirements as well. Which indicates they don't want to be judged based on the probability that pilots will not turn off the EAI.