April 20, 2009 | Mark Paradies

Monday Accident and Lessons Learned: When Could a Root Cause Be an “Other” on the TapRooT® Root Cause Tree®

Here’s the initial report from UK Air Accident Investigation Branch about the crash of a Super Puma helicopter in the North Sea:

AAIBReport.pdf

And here’s another story about the crash:

http://www.flightglobal.com/articles/2009/04/10/325055/crashed-super-pumas-gearbox-suffered-catastrophic-failure-inquiry.html

Note that due top a previous crash, these helicopters were required to have their magnetic drain plugs inspected for metal. This particular helicopter had been inspected (34 flying hours prior to the accident) and a small chip of metal was found. However, the report by the AAIB states:

” … during the period between the discovery of the chip and

the accident, no signs of an incipient gearbox failure were detected.”

So far, the AAIB’s failure analysis of the crash damaged epicyclic reduction gearbox (the module that failed and is thought to have caused the crash) shows no signs of how the failure started or what caused the failure.

If there was no further evidence, this might be a case of “Other” when analyzing the Causal Factor “Gearbox failed.”

What does the Corrective Action Helper® say to do in this case? The applicable sections say:

  • If you cannot progress further down the tree, then consider performing a Safeguards Analysis (Chapter 10 of the TapRooT® Book, 2008) to identify potential Safeguards that you could add to reduce the likelihood of this incident recurring.
  • If you could not progress down the tree due to lack of information, consider adding additional systems to record more information in future incidents so that your analysis can more effectively pinpoint the Root Causes. Video and voice recordings, as well as data recorders, should be considered.

In this case, the AAIB is recommending that the European Aviation Safety Agency (EASA) develop an inspection procedure for the internal components of the main rotor gearbox epicyclic module.

What’s the difficulty in developing a good procedure for this inspection? How do you know what to tell the inspector to look for?

If you had developed a Equifactor® Troubleshooting Checklist for the main rotor gearbox epicyclic module, you could use it as a tool to help develop the inspection procedure.

For more about Equifactor® Training, see: http://www.taproot.com/courses.php?d=3.

Here’s a CNN video about the crash:

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