Human error led to the crash of Yeti Airlines ATR in Nepal on January 15. One of the two pilots, also the more experienced one, would have mixed up the levers and ended up touching the one that “turns off” both engines, instead of the other, to the side, that moves the flaps in the wings. The condition is still a must as the investigation continues.
But Nepalese and Western investigators, as well as three different pilots with at least four thousand flight hours on this specimen, explain to Corriere that the dynamics, the maneuvers performed and the sounds recorded by the two black boxes rule out the technical problem and point fingers to the pilots’ activities.
The budget
A number of questions are still unanswered. There is also a hypothesis among pilots that civil aviation authorities could ask the manufacturer to change the controls to avoid the same error. Yeti Airlines’ ATR 72-500 took off from Kathmandu Airport at 10:32 local time in mid-January, bound for the new Pokhara Airport, the landing point for tourists and then to the world’s highest peaks. But a minute before landing, the plane crashed, killing 72 people: 68 passengers and 4 crew members.
The investigations
In the last few days, the Nepal Commission of Inquiry has published the preliminary report on the accident. In writing the fourteen pages, the Nepalese had the support of the French Transportation Safety Authority (BEA), the Canadian Transportation Safety Board, the European Aviation Safety Agency (EASA), and engine manufacturer Pratt & Whitney. Audio data (from Cockpit voice recorder) and flight parameters (Flight data recorder) were extracted from black boxes in laboratories in Singapore.
The third flight
This January 15, Yeti Airlines ATR 72 was scheduled for four routes between Kathmanadu and Pokhara and with the same pilots: veteran Commander Kamal Kc, 22,000 hours behind him, and Anju Khatiwada, also Commander, with 6,500 flight hours and that day in Accompanied by Kamal Kc to learn more about the new Pokhara Airport which is a short distance – but with a different runway orientation – from the old airport and was inaugurated just two weeks earlier. The two pilots had already flown a Kathmandu-Pokhara scenic flight that day, taking off from the capital of Nepal for the third segment.
The first problems
The preliminary report writes that Anju Khatiwada was at the controls on this flight, i.e. sat on the left side, while Kamal Kc was actually “supervising” on the right side as a pilot instructor. At 10:51 and 36 seconds the aircraft began its descent towards the airport. At 10:56 and 12 seconds the wing flaps are deployed to 15 degrees to facilitate the approach to the runway. The black boxes also register the landing gear extension and fifteen seconds later Anju Khatiwada switches off the autopilot. Immediately afterwards, the captain instructs Kamal Kc to set the flaps to 30 degrees and he repeats the instruction. “But the ‘Flight Data Recorder’ shows no movement of the landing flaps,” the investigators write.
The “flag” propellers
Instead, the black boxes register a sudden drop in performance of less than 25% for both ATR engines. The document speaks of the “sprung state” of the engines. “This means that the propellers fly in the direction of flight, so parallel to the direction of flight,” one of the pilots interviewed told Corriere. “Engines don’t actually produce thrust or drag anymore.” Usually this maneuver is performed “when the engine dies and it is necessary to create the least possible drag with the propeller: instead of placing it perpendicular to the air, it is placed parallel”.
The first aid and pain of the relatives of the passengers of the plane that crashed near the airport of Pokhara in Nepal on Sunday morning: 72 people on board (EPA)
“No energy”
“Both of Yeti Airlines’ ATR engines went into ‘idle’, at least to avoid excessive exertion,” the pilots agree. At 10:56 and 36 seconds the Cockpit Voice Recorder saves a first on-board trouble signal in the audio file. The two commanders start consulting the flight manuals to find out what’s going on. At 10:56 and 07 seconds Anju Khatiwada was twice told that the engines had no power and eleven seconds later orders passed to Kamal Kc. Meanwhile, Khatiwada reiterated that the engines had no power.
The impact
At 10:57 and 24 seconds, at an altitude of 95 meters, the joysticks begin to vibrate because the aircraft’s nose has exceeded the maximum safety values. “At this point, the ATR starts to falter,” the experts explain. The situation becomes irrecoverable: at 10:57 and 26 seconds, the plane suddenly turns to the left – a scene recorded by a person who is at that moment on the terrace of his house – and six seconds later the ATR crashes. The two black boxes stop recording data at 10:57 and 33 and 10:57 and 35 seconds, respectively.
The dynamic
But how was it possible to “shut off” the two engines in flight? Whoever is helping the Nepali investigative team explains that the most accepted hypothesis is an exchange of levers. Instead of the flap control, the pilots may have touched the propeller control: both levers are next to each other. «In all probability – explain two pilots – the captain did not lower the lever of the flaps to bring their angle from 15 to 30 degrees, but he touched that of the propeller adjustment, which, when brought back from the “auto” state becomes “Ftr” causes the engines to be deprived of power».
Without escape
Should the dynamics be confirmed by the final investigation report, the experts are amazed at how it was possible not only to mix up the levers, but also to ignore the various alarms that usually go off in this case. At such a low altitude – the pilots explain – the plane didn’t stand a chance and they couldn’t even solve the problem.