In 2004 two Pinnacle Airlines pilots flying a leg with no passengers decided to "have some fun" and fly their CRJ200 to its published performance ceiling of 41,000'. That's a little bit like driving your car at 200 km/h, without regard for road conditions, just because the speedometer goes up that far. They exceeded the recommended climb rate, never reaching the published minimum speed for that altitude, and ran one of the engines 300 degrees above its maximum operating temperature. They also did not take into account the non-standard temperature, which lowered the performance ceiling. The airspeed was so low that the stick shaker was activating, and both engines flamed out. They recovered the stall and attempted to restart the engines, but could not, and without the engines they couldn't hold altitude. They did not inform ATC of the extent of their problem and bypassed four possible landing airports before attempting an off airport landing in the dark. Both were killed and the aircraft was destroyed in the ensuing crash.
For more information see the NTSB report and the cockpit voice recording transcript. The NTSB called it unprofessional behavior poor airmanship and inadequate training. They were even nominated for a Darwin Award. But that's just background. Their escapade is not what this blog entry is about. It's that the engine manufacturer has taken some blame.
No, Pinnacle didn't sue the pilots' families and initial training organization to recover the cost of the fine airplane they lost. The families of the pilots sued the engine manufacturer for not making it clearer that if you did unspeakably stupid things with their engines, they were unlikely to continue functioning. And now the FAA has mandated changes to the General Eletric CF34 turbofan engine based on this crash.
The FAA have concluded that "excessive" friction between the static and rotating portions of a certain engine seal, under certain high-power, high-altitude conditions is unsafe and must be corrected. This is a mandatory airworthiness directive, so over two thousand such engines will have to undergo a modification, costing their operators ten hours per airplane. GE says it respectfully disagrees that there is an unsafe condition in the engine. They tried to get the FAA to explain it as a measure to reduce friction to facilitate an engine start after a high-altitude dual flameout, "an engine condition that is extremely rare," but the FAA declined.
It's true that these engines were very sensitive to the high angle of attack they were subjected to, and the pilots didn't realize that. The piston engines on training airplanes can be run at full power during a stall and the airplane doesn't care. After a period of high angle of attack and low speed, the reduced engine cooling will cause a rise in engine temperature, but the engine isn't dependent on the airflow for its very rotation the way the turbofan is. Once the engines stopped rotating they were going to be very hard to restart. Perhaps someday someone else will get these engines flamed out in coffin corner and the modification will keep them turning long enough to get them to safety.
I think the FAA decision is unfortunate, not so much over twelve thousand hours of upgrade work on CF34 engines, but that the wording of the AD may help the legal case against the company. In the 1980s, general aviation aircraft simply stopped being manufactured because the companies couldn't bear the legal costs of survivors suing them when pilots (or in some cases non-pilots in stolen airplanes!) asked airplanes to do things they weren't designed to do, and died. Jim Campbell of the Aero-News Network has a more strongly worded opinion on the situation.