NTSB Pinnacle Probe: CF-34 Engine Flaws

CollinsProLine

CollinsProLine

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According to the latest findings, once the Pinnacle pilots put themselves in a bad situation and stalled both engines, they had no chance of restart because the engines locked up due to "engine core lock". Any thoughts?

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Pinnacle Probe Unveils Training, Engine Flaws
Aviation Week & Space Technology
06/20/2005, page 49
Frances Fiorino
Washington

NTSB findings show that the crew attempted restarts according to manufacturer and company guidelines. However, the attempts were unsuccessful.

"If just one of the two stalled engines had restarted, this accident would never have occurred," said ALPA Chairman of Safety Terry McVenes. "The crew followed proper procedures. . . .But both engines failed to start because they had suffered "core lock--a risk previously known only to engine and aircraft manufacturers."

The engine core lock phenomenon is not well-known or understood throughout industry. The term refers to the seizure of the engine's core, or inner spool, by differential cooling that causes parts to bind.

Bombardier said every "prone" aircraft (CL300, CL604, CRJ200, DHC-08) is tested prior to delivery. During initial aircraft certification, engines are forced to 0% core speed and the aircraft is accelerated to confirm that engines will not lock up and can be windmill-restarted. The manufacturer said the CF34-3 engine series has two areas suspected of causing core lock-up: the outer balance piston seal and inter-stage seal. The latter was found to be a contributor and a design change was implemented, reducing the lock-up phenomenon to 1.5%.
 
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According to the latest findings, once the Pinnacle pilots put themselves in a bad situation and stalled both engines, they had no chance of restart because the engines locked up due to "engine core lock". Any thoughts?

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It's the old "3 strikes you're out" rule of accidents. Never just one thing. If they had managed the airplane better, if the engines hadn't core locked and if they had told the controller they had no engines running and turned for an airport immediately.
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One thing is for sure, if the operators didn't know about core lock in these engines, they sure will now.
 
I don't buy that there's anything majorly wrong with the GE TF/CF-34 series of engine. I flew with that engine for 5 years on the A-10, aside from being underpowered somewhat, it's extremely fuel efficient, and tough as heck. It gave me no problems in the time I flew with it because I operated it within it's design envelope. I once had an inspection panel come off the top of my plane inflight and get ingested into the right engine. It chewed up the part and spit it out the back, with nothing noticable in the cockpit gauges. No damage to the engine other than a few blades that had to have some nicks smoothed out and a complete borescope was passed with no problems. Had this been an F-16 P&W200/220, the engine would likely have shelled out and been destroyed.

In USAF training, we were taught about what is referred here as "core lock" as a probable situation for higher altitude flight (not that we'd go there in the A-10) where a high-temp engine shutdown might cause sufficient damage to warp the engine core. In this event, though a windmill start may not work, it was thought that the ATS (Air Turbine Starter) has enough torque via the APU at a lower altitude and could overcome the condition and get the core rotating again, depending on the extent of damage. It appears this crew recognized that the windmill start wasn't working, and attempted the APU start, keeping in mind that they were operating at night, with no power, on flashlights since the power was out, with no cockpit pressurization, and on oxygen masks, trying to restart engines and fly to an unfamiliar field. A very tough situation, yes. One they should never have put themselves into in the first place.
 
They exceeded the design limits of the engine. Period. This due to not operating within the proper flight envelope. Should they publish information about the limits and flaws of wing spars, so just in case someone wants to try and pull 5 Gs in a CRJ and the wings fold, they'll know better?
 
Once you start exceeding design limits on powerplants or airframe, all bets are off - period.

We had an engine overtemp on us once during a false windshear indication from the ART (Automatic Reserve Thrust) feature of the aircraft.

Long story short, the difference between the maximum operating temperature of the engine and having to literally pull the engine from the pylons and conduct exhaustive testing and inspection isn't as much as we think it is.
 
The right engine hit the maximum recordable temperature that can even be read... 1250 ITT.


Not to mention.... if you lose both engines you are to hit .7 mach/ 240 kias until you decide that a windmill start is not practical. That is to keep the core still rotating. Looking at the FDR they never hit that speed.
 
Max continuous is 580C on the (dang, whatever type engine is on the MD-88) and we hit like 620C or something, which is fairly close to the maximum inflight restart temp. There was A LOT of activity going on to confirm that it was in fact the temperature that we saw (and confirmed by a BITE check) because a couple degrees more and it was going to be unleashed hell for the mechanics.

But exceeding the maximum recordable value, yow, game over.
 
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