Posted on 02/09/2023 12:20:18 PM PST by BenLurkin
The propellers of both engines of the Yeti Airlines aircraft that crashed in Nepal last month and killed 71 people, including five Indians, did not have power during its descent, a PTI report quoted government-appointed panel probing the aviation disaster as saying.
During the analysis and investigation, the propellers of both engines were found to have gone “feathering in the base leg in the course of landing,” My Republica newspaper reported, quoting the panel.
Yeti Airlines flight 691, after taking off from Kathmandu’s Tribhuvan International Airport on January 15, crashed on the bank of the Seti River between the old airport and the new airport in the resort city of Pokhara.
Feathering applies to turboprop aircraft and is done when there is an engine stall, an aviation expert said. Usually, a propeller is feathered when the engine fails to produce the power needed to turn the propeller. By angling the propeller parallel to the direction of the flight, feathering helps in reducing the drag on the aircraft, the expert added. Fifty-three Nepalese passengers and 15 foreign nationals, including five Indians, and four crew members were on board the plane when it crashed, in one of Nepal’s worst aviation disasters in over three decades. There were 72 people onboard the ATR-72 aircraft when it crashed, but rescue officials have so far managed to recover only 71 bodies with the other passenger presumed dead.
The Yeti Airlines tragedy in Pokhara is the 104th crash in Nepali skies and the third biggest in terms of casualties.
It will feather the prop when the engine fire button are hit.
To my knowledge props can only be feathered by deliberate human action with dedicated controls for feathering. From the brief video it appeared left wing stalled and plane went into spin. Would indicate plane just going too slow on approach.
Ran out of fuel?
Mind thy airspeed lest thy ground speed rise up and smite thee.
It will feather the prop when the engine fire button are hit.
The crash video is pitiful
Alive one instant
Dead the next
“From the brief video it appeared left wing stalled and plane went into spin. Would indicate plane just going too slow on approach.”
If one prop is feathered then you have asymmetrical thrust. If he was on approach he might not have enough reaction time to prevent a crash.
Correctomundo and I stand corrected...some planes do indeed have auto feathering capability.
Practically every turboprop made that isn’t running Garretts will auto-feather. And many recips as well (provided it has a constant-speed propeller).
In most turboprop engines (except Garretts) and most recips with constant speed propellers, engine oil pressure delivered to the propeller dome drives the propellers OUT OF feather. Which means when you shut it down, it automatically goes to feather. If the engine poops the bed in flight, as oil pressure falls off, the prop goes to feather automagically.
Garretts are different (and AFAIK it’s only Garretts, but I might be wrong). They need oil pressure to drive the props INTO feather. Shut a Garrett engine down and its props go to full pitch. So if the engine dies, you have a limited window to feather before there’s no oil pressure.
The only legitimate reason for both being feathered would be a double engine failure. But those are exceedingly rare — like drawing straight flushes two hands in a row rare — except in cases of fuel starvation.
All of the US Navy’s aircraft are multi-engine except maybe some reciprocating engine trainers and the F-35. And they still lose an airframe on average once every 3-4 years due to fuel starvation. And they should know better.
That both props were feathered could mean somebody who shouldn’t have feathered an engine that didn’t need it. The engine-out emergency procedure would have had a guard against that very occurrence, but that’s why they put the “human” in human error.
The determination that both engines were feathered probably was made by examining the position of the control levers in the cockpit. If they’ve been over the wreckage in that detail, that means they’ve also already checked to see if the fuel tanks were dry. That there was no mention of fuel starvation would give me to believe the evidence ruled out that possibility.
Whether that means they crashed with one operating engine, who knows?
Thanks for knowledgeable commentary.
Will be interesting to see what the ultimate cause and sequence of events were. Most of the time so the experts say, there is no one thing but rather a series of events.
It's certainly possible. I worked aircraft instrumentation in the Air Force and occasionally we'd have to remove the entire instrument panel to facilitate some other maintenance. One time when reinstalling the panel, one of our guys laid down upside down facing the rear and connected all of the engine instruments backwards - left engine readings connected to the indicators on the right side of the panel. There was talk of court-martial, but they realized the Crew Chief didn't notice when he ran up the engines following the repairs, not to mention it was only on the third flight following the screwup that the pilot reported the reversal, and I think he flew the flight anyway.
Sorry, I should have noted that ATRs all use Pratt & Whitney engines. The only a/c that use Garrets are odd ducks like the Mitsubishi MU-2, Fairchild Metroliner (AKA the Flying Lawn Dart), the BAE Jetsream, and IIRC the Beechcraft B100 (most King Airs use P&W PT6s).
As for the loss an an engine being the cause of the crash, the best place you could possibly lose an engine would be on descent at your destination because you’ve burned off your en-route fuel, so the a/c is light, and you don’t need much power because you’re going down hill the rest of the way.
The ATR 72 is well capable of taking off and climbing out if it loses an engine on take-off roll (provided it happens after reaching V1 airspeed), so losing one on descent to arrival shouldn’t be a big deal (that’s what commercial pilots are trained for, and paid to do). IF — big-eye, big eff — IF that’s all that went wrong.
Never heard of that. Interdasting.
A stall doesn’t cause an engine to feather, much less two at the same time.
Which also means less drag.. which in turn would suggest the pilot intentionally feathered both engines to extend his glide. Which means probably ran out of gas, which suggests he dove for the airfield, mismanaged his energy, and stalled in the turn.... Low, slow, and out of ideas. Unfortunately most pilots have miniscule experience with handling their plane in an unpowered glide as it is required so seldom. Nothing ever happens until it does.
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