Originally published at: Guest Post: A Systems Safety Look at UPS Flight 2976
The case shows how legacy certification decisions can persist even after service history points in another direction.
Perhaps you can speak to FAA’s “Aging Aircraft” inspection program and how it applies to this accident.
Overview
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The FAA’s Aging Aircraft Maintenance Program is a suite of strict regulations and supplemental inspections designed to prevent age-related structural degradation—such as metal fatigue, widespread corrosion, and cracking—in aircraft. It applies to mature fleets to ensure their continuing airworthiness and structural integrity. [1, 2]
First, I don’t know how anyone could logically downgrade the classification of an engine pylon mount to anything less than “Primary Structure”. Second, it sounds so utterly typical of how the bureaucratic FAA works and thinks to discuss failure rates of parts without regard to the lives that depend on getting it right. In other words, it was more important to show the numbers than it was to act on what those numbers were telling them.
Excellent and informative article Teresa. It gives people like me who are not experts in safety some insight into what went wrong in the process. And maybe how we can be more attentive at managing the maint on our own aircraft and focusing on safety critical systems in terms of inspections, service bulletins, etc. For example, some Pt91 mechanics view SBs as items to be ignored because they are not mandatory. As owner-operators we are ultimately responsible for managing the maint on our personal planes and maybe could take the approach you propose into consideration.
This is my understanding. The pylon is primary but the bearing inside the pylon is secondary. The failure of the bearing caused fatigue in the pylon by creating non-uniform loads in the pylon. It’s not like the bearing was completely obliterated. It just cracked in half along the path for the grease. It was still taking up the load just not uniformly. And that caused fatigue on the pylon. I don’t fault MD now Boeing for making this assumption when the aircraft was designed. I do fault them for ignoring or not connecting the data to the original assumption.
Part of my job is risk identification and management. A good place to find risk is in your assumptions. The problem I’ve discovered as a senior engineer is that many engineers, junior or senior, don’t understand when they or others have made an assumption.
Thanks, in advance of reading it I point to a grammatical sequence problem or omission - an explosion occurred while airborne, just after the engine flipped over the wing. Of course an even larger explosion occurred when airplane hit the ground.
As the author stated, the original risk assessment placed this as a secondary structure. Unfortunately, the data was there, when the bearing failed, lugs were starting to deform.
Kind of a catch-22. Boeing didn’t design it, so they accepted the certification data. The real failure is the failure of the FAA SDR system. Numerous SDRs had been filed. This should’ve been the red flag. Of course the icing on the cake was the application to extend the inspection interval. Almost like the left hand at Boeing wasn’t talking to the right. (Which in large organizations, is usually the truth). The data was there. The issue is what it would take to flag it before a catastrophic failure occurred
As with many of the regulations, changes resulting from this accident come at the great cost of life and property. We’ve learned too many ‘lessons’ recently, this accident and the Washington D.C. midair to name a couple.
I hope we as an aviation community, can extrapolate from these events, learn from them, and make the necessary changes to make flying safer. In this way, we will be honoring the memories of those that paid the ultimate price.