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New Safety Risks Under Scrutiny on Boeing’s 737 Max

salawat 7y ago
Hmmph. Seems like they're starting to actually pay more attention, but I'm noticing a few patterns in the problems they're finding. A) Overoptimism in terms of estimation of likelihood. B) Lack of attention to 2nd order effects of modifications (grinding down a panel on the engine compromising a lightning protection material) C) Still not seeing the QC I'd expect If they are just now finding out about rotor weaknesses. Also, as I recall, there was some concern over whether or not the nacelle would even contain a thrown blade a while ago. I don't remember hearing anything on a resolution to that, or am I misremembering?
- kayfox 7y ago
  The blade containment is part of the engine itself, which is made by CFM. CFM has had some issues with the generation before LEAP and blade failure, but the last I looked at the reports it appears the blades were contained on the accident flights, its just the cowling caused issues. Example of one of the incidents: https://en.wikipedia.org/wiki/Southwest_Airlines_Flight_1380 https://en.wikipedia.org/wiki/Southwest_Airlines_Flight_1380 Boeing would be responsible for the cowling design, and has been directed to update the cowling design based on the new models created based on this incident. The failure is not really as much a failing on Boeing's part to design it correctly in the first place, but a lack of data indicating certain unforeseen blade trajectories are possible on failure. Now that these are a known thing, they will be incorporated in design updates throughout the industry. Final report: https://ntsb.gov/investigations/AccidentReports/Reports/AAR1903.pdf https://ntsb.gov/investigations/AccidentReports/Reports/AAR1...
chopin 7y ago
Sounds a bit like another attempt of Boeing to blame pilots (reacting not fast enough). Pilots cannot react correctly to a system they have no knowledge of. NYT could have done a better job in pointing out that the observed failure mode of MCAS did not look like a trim runaway and sent out other alerts caused by the defective angel of attack sensor (unreliable airspeed).
- kayfox 7y ago
  The discovery that there's a gulf between what the Boeing engineers (many of whom are pilots) and the FAA previously thought of as runaway trim, uncommanded trim movement, and what they now know about this behavior not being recognized, means that many systems risk factors will get reclassified and thusly will have to be redesigned to be more robust. In this case, one of the main modes for the electric trim running away has been shorts in that system's wiring harness, so it now has to be redesigned because Boeing can no longer rely on the pilots recognizing it. I bet speed trim will get a revamp too.

Hmmph. Seems like they're starting to actually pay more attention, but I'm noticing a few patterns in the problems they're finding. A) Overoptimism in terms of estimation of likelihood. B) Lack of attention to 2nd order effects of modifications (grinding down a panel on the engine compromising a lightning protection material) C) Still not seeing the QC I'd expect If they are just now finding out about rotor weaknesses. Also, as I recall, there was some concern over whether or not the nacelle would even contain a thrown blade a while ago. I don't remember hearing anything on a resolution to that, or am I misremembering?

kayfox 7y ago
The blade containment is part of the engine itself, which is made by CFM. CFM has had some issues with the generation before LEAP and blade failure, but the last I looked at the reports it appears the blades were contained on the accident flights, its just the cowling caused issues. Example of one of the incidents: https://en.wikipedia.org/wiki/Southwest_Airlines_Flight_1380 https://en.wikipedia.org/wiki/Southwest_Airlines_Flight_1380 Boeing would be responsible for the cowling design, and has been directed to update the cowling design based on the new models created based on this incident. The failure is not really as much a failing on Boeing's part to design it correctly in the first place, but a lack of data indicating certain unforeseen blade trajectories are possible on failure. Now that these are a known thing, they will be incorporated in design updates throughout the industry. Final report: https://ntsb.gov/investigations/AccidentReports/Reports/AAR1903.pdf https://ntsb.gov/investigations/AccidentReports/Reports/AAR1...

chopin 7y ago

Sounds a bit like another attempt of Boeing to blame pilots (reacting not fast enough). Pilots cannot react correctly to a system they have no knowledge of. NYT could have done a better job in pointing out that the observed failure mode of MCAS did not look like a trim runaway and sent out other alerts caused by the defective angel of attack sensor (unreliable airspeed).

kayfox 7y ago
The discovery that there's a gulf between what the Boeing engineers (many of whom are pilots) and the FAA previously thought of as runaway trim, uncommanded trim movement, and what they now know about this behavior not being recognized, means that many systems risk factors will get reclassified and thusly will have to be redesigned to be more robust. In this case, one of the main modes for the electric trim running away has been shorts in that system's wiring harness, so it now has to be redesigned because Boeing can no longer rely on the pilots recognizing it. I bet speed trim will get a revamp too.