Comments about technological history, system fractures, and human resilience from James R. Chiles, the author of Inviting Disaster: Lessons from the Edge of Technology (HarperBusiness 2001; paperback 2002) and The God Machine: From Boomerangs to Black Hawks, the Story of the Helicopter (Random House, 2007, paperback 2008)

Sunday, April 3, 2011

Southwest B737-300: Rapid descent to Yuma

Quick post on the news item Friday about Southwest Flight 812, Phoenix to Sacramento, which had to make an unscheduled landing after a section of skin roughly 3 x 4 foot in size blew out from the top of its fuselage. One passenger said the location was around Rows 12-13. Tail number is N632SW. It was manufactured in 1996. Over 930 model 737-300s are flying worldwide 

For pilot enthusiasts, here's a link to what appears to be a Boeing manual that includes a section on rapid descents. See material starting on PDF page 209: advice is to limit airspeeds and maneuvering loads if structural damage is suspected (or confirmed, given a big hole in the cabin).

The discussions on and, a pilots' forum, are worth reading. It is disappointing to read about several years of maintenance shortcuts by Southwest management, and clashes with regulators. 

A NTSB link to a skin blowout incident on an Aloha Airlines 737 is here. A Time article on that one is here. It was fatal to one flight attendant who was sucked out of the cabin. (But the Aloha plane didn't crash as in a previous cabin-skin failure, of a Far Eastern Air Transport 737-200 in 1981.) For more context, see this Airsafe list of 737 crashes

That said, the 737 is a workhorse and has accumulated an impressive safety record. But apparently some of its operators can do better. Inspections and prompt repairs, done by the book, are key. 

I'm told that all aircraft have cracks in them somewhere, if one looks closely enough. While writing my helicopter book I was surprised to be shown how a helicopter company manages tiny but visible cracks in rotor blades on executive helicopters, found during periodic inspections. These blades are so expensive that cracks once detected, if well below a risk threshold, are monitored and managed, rather than replacing the entire blade.

Back to airliners. One catastrophic risk in fuselage-blowout cases, even those in which the lower section of the aircraft remains structurally sound, is collateral damage to wiring harnesses, control cables, or hydraulics that happen to be routed nearby. This is not a small matter.

You can see a wiring bundle at the center of this widely distributed photo from the Flight 812 incident. Normally it's concealed behind a ceiling panel but was exposed by the blowout.

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