PPRuNe Forums - View Single Post - Korean Air A330 off runway in Phillipines
Old 24th Oct 2022, 23:16
  #30 (permalink)  
tdracer
 
Join Date: Jul 2013
Location: Everett, WA
Age: 68
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Originally Posted by fdr
"Louder 004" raised two things:
1. The failsafe autostow system didn't on the PW4060...
2. the modeling of controllability did not acurately account for the lift loss in the wake of the engine's reverse plume or the added drag from that cause.
Actually, auto-restow actually contributed to the accident. Although we never positively identified why the Directional Control Valve (DCV) changed state from 'stow' to 'deploy', a mis-rigged auto-restow sensor (indicating the reverser wasn't stowed) activated auto-restow which opened the Hydraulic Isolation Valve - providing hydraulic pressure to the reverser so that when the DCV changed state the reverser deployed.
I was directly involved in the Lauda investigation (BTW, one of the most unpleasant things I've ever done - I could never be an accident investigator, I found it too painful). They'd actually done a flight test on a 767 when they deployed a reverser in flight - but they'd done it with the engine already at idle, at 10k/200 knots. Lauda happened with the engine at max climb, 24k/Mach 0.78. Although the FADEC automatically commanded idle, at those conditions it would have taken nearly 30 seconds for the engine to reach idle - by which time it was way too late and the aircraft was already starting to break up. I participated in a wind tunnel test with a deployed reverser at Boeing Vertol in Philly. There was a rather annoying Aero S&C type that insisted the aircraft was controllable and the Lauda pilots messed - at least he did before we started testing. After he started seeing the data, he got real quiet. Although there was a time when I might have understood all those controllability coefficients, after over 15 years of working engines I'd forgotten all that S&C stuff. However at the end of the test, we did a flow visualization using hundreds of yarn tufts. THAT just anyone could understand - with the engine at high power nearly the entire upper surface of that wing was separated . They never stood a chance.
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