Sioux City DC-10 rotor failure

Preview of Brian Hohmann's guest lecture. Titanium nitride inclusion in cast titanium disc; fatigue crack; both tail-mounted engines lost; emergency glide landing.

This is only my fifth lecture, but I'm gone all next week. So Brian Homan [Hohmann] will be lecturing on the example of the Sioux City, Iowa crash and the problems of inspection and quality control. Anybody know about Sioux City, Iowa? It was probably back in the 1980s, so only a couple of us were alive then. A disc in a GE engine blew up. It's McDonnell Douglas, because they had both engines in the back on the tail. It wiped out both engines when it went.

Rotor disc failure on UAL 232 cut all hydraulic control cables; pilot landed without control surfaces. Used to illustrate why FAA focuses fatigue-crack-growth attention on rotors and shafts rather than blades.

Just to give you an idea of the cost of these things, the CFM56 engine, which is on the 737 and a bunch of Airbuses, is the most widely used commercial engine in the world. It has two stages — they've designed it to have few stages, because the fewer stages the better off you are. Now the critical components on an engine, the ones they really worry about, are things like the big rotors that those things go on, or the shafts. You lose a shaft or you lose a rotor, you lose the engine, because when one of those things breaks there's enough energy in one of those big heavy things that it'll cut the plane right in half. That's the Sioux City Iowa problem — they had a rotor failure, it went through and cut all the control cables, and the pilot had to basically fly without any of his flaps. He had to land without any regular control surfaces. So the FAA spends lots of time on defects and fatigue crack growth in rotors and shafts, because these things weigh hundreds of pounds.