737MAX wrote: ↑
14 Mar 2019, 11:28
Every single system can fail. The runaway stabilizer NNC is nothing new. This particular issue happened before, also on other planes than the 737 MAX ! There is absolutely NOTHING wrong by switching off the stabilizer trim. Read the bulletin published by Boeing after the Lion Air crash here: https://theaircurrent.com/aviation-safe ... air-crash/
Every single system can fail, but a not at the same rate. The Stabilizer trim runaway is a checklist that refers to a failure with a failure rate considered "extremely remote" because the result of the failure would be "catastrophic". BTW, I don't invent these words, they come from MSG failure analyses. MSG analyses have evolved and probably change with every new aircraft type, but it's about the principle.
In other words, the stab trim runaway checklist is a checklist that refers to failures that are extremely remote, and followed intensively through the implementation of a maintenance planning. That's why we have A,B,C,D checks, checks expressed in cycles, checks expressed in flight hours... to check the system within the failure timeframe and have a follow-up.
The Airbus problem is the same: it is based on a dual AoA failure, not a single. What is the chance to have a failure of system A with a certain failure rate, after system B with a similar failure rate. All these things are statistical methods to define checks and maintenance manuals. This doesn't mean it cannot happen, but the chance is extremely remote. This is pure statistics, but aircraft safety is... nothing but statistics checked on a timely basis in reality.
Back to the 737max, something apparently is very wrong in the failure analyses. The failure has had 2 times catastrophic results. Whatever checklists you want to throw at it, the reality is what it is. You cannot rely on a checklists designed for "extremely remote" failures to "save the situation" for something that is not extremely remote, but something that can happen every 6 months. If the failure re-appears, you should be able to identify and handle this with very little intervention. That is safe for a 6 months failure rate.
Nobody talks about the number of times it has already happened, maybe we only see the tip of the iceberg. Even scarier, IF it only happened twice, reality is what it is and the result is deadly: it occured twice, twice catastrophic result.
Not ONE SINGLE PILOT should in this case think he can save the day with his checklist. You weren't there. You don't know if the pilot were thrown up & down, you don't know if passengers were hitting the ceiling of the aircraft. The fact is they crashed. Twice. Whatever the cause.
If both crashes had the same cause.
But IF that is the case, than a simple failure that Boeing statistically allows to happen every 1000 or 100000 flighthours, has the ability to catastrophic events within that timeframe: that is NOT airworthy and a design error, whether you as a pilot can handle it or not. And if you think you can, this world ain't Top Gun, we don't go land on the moon. We all have families and do this to live. That's safe aviation.
You do NOT takeoff to do memory items.