PPRuNe Forums - View Single Post - MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures
Old 29th Jul 2019, 01:29
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Jim_A
 
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Originally Posted by fdr
As disappointing as the saga of the MCAS is, the subject of the rudder control runs and the perception of a threat from a liberated fan blade should be considered rationally. A mob lynching doesn't assure the industry achieves what it needs, and would almost certainly lead to unintended consequences in due course.

MCAS's morphing of design wth what appears to be inadequate hazard analysis was disastrous. It is interesting to follow the discussion that arises on the altered relationship of the manufacturer to the regulator due to the ODA approval process. EASA has an equivalent process, DOA, for exactly the same reasons, and dependent on the same safeguards. ODA/DOA depend on a robust QA process, and it is that part that has let loose in the Max case. The regulator change to ODA/DOA is a consequence of rational realisation that the regulators are starved of manpower being unable to compete in most cases with the industry salaries. Adequate oversight requires retaining competency and staffing levels that is not possible in the current minimum funding of regulators. In principal, with good QA oversight, the ODA/DOA system in a substantial improvement over previous processes, but the entity's ethics on QA is central, and TBC's history of abuse of QA engineers places some doubt on that; they need a corporate clean out of ethics for real, not a repeat of the last effort arising from the KC-767 saga, where there was no acknowledgement of their actions on the B737 parts fabrication scandal.

The rudder... For 50+ years the plane in question has flown without an incident of a primary control being severed by an uncontained fan failure. The engine and nacelle design is supposed to protect from a liberated fan as part of the certification requirement. In the case of the 737, the SWA B737 in flight failure passing by Pensacola resulted in a fatality of a passenger, as had the MD82 disk failure years before. The risk to the aircraft that is not able to be mitigated arises from disk failure, not singular fan blades. In general, as seen on UAL232, QFA032, and the AA B767's, a disk failure is potentially a catastrophic event, the defence is not having them, and that comes from having good metallurgical design and processing, good structural design, and as much redundancy as possible in critical systems architecture. QFA032 showed that you can still have a bad day, and not just because the manufacturer is Boeing and the product is called a Max.

I would have more interest in sorting out the manual trim issues by at a minimum providing a training program to remove the cobwebs of time past than to worry over a fan blade issue, where the risk of a disk failure is vastly more problematic and almost impossible to mitigate, it is to be avoided.
I was thinking the same thing about turbine disc failures. It seems to me that issue has caused more grief to aircraft than shedding fan blades.

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