Nepalese authorities say an instructor pilot on the Yeti Airlines ATR72 that crashed in Pokhara in January may have inadvertently feathered both props while trying to lower the flaps. The plane crashed while on final for the new airport in the Nepalese resort town and was a familiarization flight for the other pilot. A translation of the Nepalese Aircraft Accident Investigation Commission preliminary report says data from the cockpit voice and flight data recorder suggests that as the crew set up for landing, the instructor pilot pulled the wrong lever. The flap and prop levers are next to each other in the ATR72.
“At 10:56:27, the PF (Pilot Flying) disengaged the Autopilot System (AP) at an altitude of 721 feet Above Ground Level (AGL). The PF then called for ‘FLAPS 30’ at 10:56:32, and the PM (Pilot Monitoring) replied, ‘Flaps 30 and descending,’” the report said. “The flight data recorder (FDR) data did not record any flap surface movement at that time. Instead, the propeller rotation speed (Np) of both engines decreased simultaneously to less than 25% and the torque (Tq) started decreasing to 0%, which is consistent with both propellers going into the feathered condition. When propellers are in feather, they are not producing thrust.”
Video shows the aircraft slowing and then falling off to the left. It crashed on the edge of a gorge and all 71 people onboard were killed. Weather was benign at the time. The airport had been open for less than two weeks and Yeti was one of the first carriers to use it. Both pilots were captains and the pilot flying was doing a checkride into the new facility. The new airport has an 8200×150 runway.
And they both realized they had no power from the engines, and still allowed the aircraft to slow to stall-spin. Alternatives probably weren’t good at that point, but stalling an aircraft in from that altitude has only one possible outcome.
Yes – that’s the other part that’s not being discussed. Altitude means available thrust. Why didn’t they pitch down and at least avoid the stall and un-survivable fall?
Doesn’t feather props make a lot more and different noise? Could it not be felt that the plane was behaving differently?
Maybe it felt and sounded similar to the drag of flaps being extended? I haven’t flown the ATR, but then few ATR pilots have probably feathered the engines in flight.
An ATR training captain @flywithmagnar wrote about this report:
“As an ATR pilot and instructor for more than 20 years, I find it unbelievable that this could happen. Even so, the pilots had several opportunities to rectify the error. When a propeller goes into feather, it produces a distinct sound. When the flaps is extending, the aircraft pitches up, and the pilot has to push the nose down and trim the aircraft. The single chime from the Crew Alert System was most likely triggered when the AC “Wild” generators driven by the propeller gearboxes went offline. As a consequence, hydraulic pumps and ice protection systems were disabled as well. When reading the Before Landing checklist, the pilots are supposed to check the position of the flap lever and the indicator. But what really puzzles me, is that the flaps was extended to 30 degrees after the checklist had been completed. Was this communicated to the other pilot? The preliminary report doesn’t tell much about what was said in the cockpit. And there might be factors we are still not aware of. The investigation will definitely focus on human factors.”
Not an ATR pilot, but looking at the picture, it seems pretty hard to understand how one could mistake the TWO apparently roundish prop knobs from the SINGLE flap-shaped flap handle.
Back in the 80s, a Delta 767 crew shutdown both engines on departure from LAX. They got an EEC fail EICAS message and procedure was to turn off both EECs which requires one to lift a guard on the square EEC switch and press the button. Instead, they shutoff the engines by pulling up out of the detent and lowering the mushroom shaped fuel cutoff switch.
Human factors, you never know when it will strike.
As an old ATR Driver with several thousand hours of 42 and 72 time I cannot wrap my head around how those guys could do what they did and not notice and fix it. They missed the pitch change, the prop noise change, and every other clue that things were messed up. Instructor pilots and Captains are not gods and sometimes you need to yell at them and fly the airplane.
Flew the ATR-72 at a Regional and I’m amazed this occurred. The difference in shape of the knobs should have been felt and noticed by the IP. Unbelievable.
The pilot also has to lift a latch to move the condition levers.
I was thinking that too but it’s been a number of years since I flew it.
Back in the 80s, a Delta 767 crew shutdown both engines on departure from LAX. They got an EEC fail EICAS message and procedure was to turn off both EECs which requires one to lift a guard on the square EEC switch and press the button. Instead, they shutoff the engines by pulling up out of the detent and lowering the mushroom shaped fuel cutoff switch.
Human factors, you never know when it will strike.
While the TransAsia crash in Taipei in 2015 was the result of a mismanaged engine failure resulting in the shutdown of the remaining “good” engine, this one is totally perplexing given the visual, aural and tactile indications described above. And why was the approach not stabilized at 1,000 ft. AGL with all checklist items completed? Not that another 279 feet would have necessarily salvaged the situation, but a few extra seconds to recognize and react to the anomaly(ies) MAY have resulted in a different outcome.
The answer is probably that they were flying a visual traffic pattern. However, a bit more than a minute elapsed from the props feathering to the stall. The pilot flying said twice, “we have no power” but neither made a correction to the condition levers.
Anyone know how long it takes for the ATR props to come out of feather? In the turboprops I have flown with either PT6 or GE (Saab 340) it can take 30-45 seconds to come out of feather. That would leave maybe 30 seconds to respond before crashing. Allowing the plane to stall instead of flying to the ground is not good either. Not many twin engine planes have a procedure in the AFM for total loss of engine power. Does the ATR?
About 30 seconds is right. It might be faster in flight due to airflow. The ATR does have a procedure for dual engine flameout, but it wouldn’t have helped in this situation.
“the propeller rotation speed (Np) of both engines decreased simultaneously to less than 25% and the torque (Tq) started decreasing to 0%, which is consistent with both propellers going into the feathered condition” How did the torque decrease when the propellers went into feather? Assuming the power is left alone, torque goes up when Np goes down. Is there something on the ATR that reduces power when a prop is feathered?
Yes, the engines and props are all electronically controlled.
Two Captains, not good, especially when one is from the training dept.
There’s a good “wrap up of events” from the preliminary report on you tube as discussed by “blancolirio”. Link here: https://www.youtube.com/watch?v=rXTy24rdwYc
Years ago, on a SA-227AT Merlin IV, I had a co-pilot pull both props back to Low RPM when I asked for approach flaps. The sound and the flight performance were unmistakable that something was wrong and I immediately pushed the props back up. Later on, while training another pilot, he managed to bring both power levers into reverse in flight. Another amazing sound and feeling! Glad that aircraft is behind me but still flying.
Wow… thank you for sharing those incidents! Clearly goes to show how even experienced pilots and crews can mess up badly when pilots are not checking on each other.
Gear up landings, pilots shutting down the good engine instead of the bad one, pilots moving the wrong levers because their mind is elsewhere or having a major brain fart in the worst possible moment… all that is documented in many accident reports, and no-one should assume they’re immune.
All “things” have a failure rate, including humans. 10E-7 sort of brain fart. About pulling the wrong lever: There but the grace of God go I.