Prime Theory Emerges in Nepal ATR Crash

Videos that came to light shortly after the crash showed the flight was in trouble. One of them, taken by a resident who lived nearby, shows the plane slowing considerably and then going out of control. The other was a Facebook livestream taken from inside the plane's cabin by a passenger who perished moments later. 

Investigators quickly recovered the flight recorders, and to everyone's surprise, they showed that the plane's two propellers had been brought to zero power output, in a condition known as "feathering," which is used in flight only after an engine has failed. Featherning it keeps the non-working engine's propeller from created excessive drag. When both propellers are feathered, neither engine will produce any power, and for a plane like the accident ATR 72, that can be catastrophic. But why did it happen? 

There's a new theory, and it makes a lot of sense to investigators. 

The flight had originated in Kathmandu and was headed to Pokhara, a 30-minute flight. Pokhara is the gateway to the Himalayas and a popular trekking jumping-off point. The weather looked a little hazy but otherwise excellent, and from the video taken by the Pokhara resident, the wind didn't appear to be a factor.

That ground-perspective video below, which stops just as the ATR is dropping a wing and before it spirals out of control, shows the regional airliner clearly flying very slowly before disappearing behind a structure. At that point, its bank angle was greater than 90 degrees, meaning it was on its way to being inverted.

The video from the cabin, likewise, shows the plane at an unusually high angle of attack as it is flown slowly for some reason. After watching the videos, a former NTSB official remarked that the plane's wing flaps didn't appear to be fully extended on the airliner and that the engines, or at least one of them, appeared to be functioning. Twin-engine commercial planes like the ATR 72 are fully capable of all phases of flight even with one engine not producing power.

If the flaps had not been fully extended, that would have raised the minimum speed at which the plane would still be controllable. It appears from the video that the plane did indeed go out of control, seemingly from being flown too slowly. Airline pilots are trained to be rigorous in their attention to the plane's configuration (such as flap settings) and its airspeed. The cabin video goes all the way into the crash, and the passengers, all of whom would die in the crash, seemed unaware until the very last seconds that they were in trouble.

The latest theory takes all of that into account. It proposes that one of the pilots, when the other called for the deployment of 30 degrees of flaps, but the flight recorder shows that instead of deploying 30 degrees of flaps (they remained unchanged) the pilot accidentally pulled back on the condition levers, which are located directly next to the flaps. There's no safety mechanism in place to prevent an accidentally grab, as the theory suggests, to turn disastrous. 

Pulling both propellers back to a feathered condition would explain the plane's slowing before going out of control and crashing. The question that remains is, if it was accidental, and there's no evidence that authorities have shared to suggest it was intentional, could the mistake have been fixed, that is, why didn't one of the pilots have simply advanced them again to regain power? And if that was attempted, how long would it have taken for those engines to spool back up to producing a usable amount of power, all while airspeed was decaying as they attempted in vain to hold the plane's altitude. In this case, the pilots might not have realized the mistake that had been made, and by the time they figured it out, if they ever did, the plane had descended below 500 feet AGL, was on the verge of an aerodynamic stall, so it's unlikely that the flight could have been saved. 

The plane crashed in a steep ravine near the new Pokhara Airport, which opened just a few weeks ago. It is not clear how flying into a new and therefore somewhat unfamiliar airport might have affected the flight, though investigators will surely be looking into that factor.

All 72 bodies have been recovered, as were the flight recorders, which might provide answers. In most cases, the cockpit voice recorder holds few clues, but this case feels very different than most.

On a particularly tragic note, shortly after officials released the names of the crewmembers who died in the crash, it became known that the pilot killed in the crash, Anju Khatiwada, was the widow of the captain who died in the crash of a Yeti Airlines flight in 2006. The pilot who was killed on Sunday became a pilot only after her husband died in the crash of a Twin Otter (an even smaller twin-engine plane) more than 15 years ago.

There are conflicting reports about the seat that Khatiwada was occupying on Sunday's flight, though some outlets have reported that she was flying with a check pilot before earning qualification to fly as captain of the ATR 72. If that were the case, the qualification process might hold clues as to why the plane went out of control, though standard procedures would call for the flight to be flown by the book regardless of the nature of the crew. Khatiwada earned her ratings in the United States and had more than 6,000 hours of flight experience, reportedly being qualified already as captain on other aircraft in the Yeti Airlines fleet.

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