Summit L410 at Lukla on Apr 14th 2019, runway excursion on takeoff and collision with two helicopters
Last Update: February 18, 2020 / 20:53:06 GMT/Zulu time
The airport reported the first officer of the L410 as well as two security officers on the ground were killed, the captains of the L410 and the destroyed Manang Air helicopter were airlifted to Kathmandu and are in stable condition. The helicopters involved belonged to Manang (9N-ALC) and Shree Air (9N-ALK).
On Apr 15th 2019 Authorities reported, the CVR and FDR of the L-410 have been recovered and are being analysed. Preliminary results of the investigation suggest, the first officer was pilot flying. He had about 18 months of experience and may not have possessed the necessary qualifications to perform the takeoff at Lukla. The aircraft immediately swung to the right after power had been applied, the crew was unable to control the aircraft afterwards. The rotors of the Manang helicopter were still spinning as the aircraft had just landed and set down its passengers. The spinning rotor probably hit the first officer killing him.
On Aug 12th 2019 Czechia's UZPLN reported according to preliminary information by Nepalese Authorities, that the crew applied takeoff power, however, a few seconds later an engine control lever was shifted and the engine power as well as propeller speed decreased. The commander reduced power however could not prevent the aircraft from running off the runway onto a heliport. The UZPLN assists Nepali Authorities in analysing the FDR and CVR.
On Feb 18th 2020 Nepal's AAIC released their final report concluding the probable cause of the accident was:
The commission concluded that the probable cause of the accident was aircraft's veering towards right during initial take-off roll as a result of asymmetric power due to abrupt shifting of right power lever rearwards and failure to abort the takeoff by crew. There were not enough evidences to determine the exact reason for abrupt shifting of the power lever.
- Failure of the PF(being a less experienced co-pilot) to immediately assess and act upon the abrupt shifting of the right power lever resulted in aircraft veering to the right causing certain time lapse for PIC to take controls in order to initiate correction.
- PIC's attempted corrections of adding power could not correct the veering. Subsequently, application of brakes resulted in asymmetric braking due to the position of the pedals, and further contributed veering towards right.
The AAIC reported the first officer (33, CPL, 865 hours total, 636 hours on type) was pilot flying, the captain (48, ATPL, 15,652 hours total, 3,558 hours on type) pilot monitoring.
The captain had taxied the aircraft onto the runway and lined the aircraft up for takeoff, then handed the controls to the first officer. After commencing takeoff the aircraft began to veer right within 3 seconds, went off the runway into the helipad and collided with two helicopters. The first officer died on the spot due to the idling rotor of one helicopter. A security officer on the ground died on scene, a second security officer died on the way while being airlifted to a hospital.
The CVR was downloaded however did not produce "no-sound" data only.
The FDR was successfully downloaded.
The AAIC analysed that the flight crew was qualified and well rested.
Tyres and landing gear were found without anomalies, all tyres were inflated. No hydraulic leaks had occurred. Those nose gear oleo was found collapsed as result of impact forces.
The nose wheel steering circuit breaker was found popped, however, the commission ruled out the CB popped out before takeoff. The nose wheel steering had been switched to rudder, the steering mechanism was found working normally. The commission wrote: "it is very hard to determine probable causes, because every component (Weight on Wheels -WOW switch, clutch, valve, relay, protection diodes) of this circuit represents potential short circuit risk. Hence, the commission narrowed down the likelihood of CB pop out is due to short circuit in the WOW micro switch circuit (common component for Manual & Pedal Part of Nose Wheel Steering circuit) as a result of nose oleo collapse after impact."
With respect to the CVR containing no data the AAIC ruled out the recording had been erased and wrote: "Considering the probabilities presented on the outcome of the analysis of why no-recording of any voice data happened, incorrect installation of the equipment on the aircraft is likely."
The AAIC analysed that all FDR data were normal until the takeoff commenced. The AAIC analysed the takeoff sequence:
Before take-off, crew has to receive takeoff clearance, check engine parameter like torque, ITT, RPM, fuel flow, engine oil pressure/temperature and takeoff callouts.
As per FDR data analysis, takeoff set torque was not same on both engines. Right engine torque was giving 33.52% torque and left engine torque was giving 44.8 % torque.
Aircraft began to veer at the beginning of steep slope of runway 24, 28 meter from the threshold. As per PIC, when he realized that the aircraft was veering towards right, he took over the aircraft controls from the copilot. Once PIC realized that the right power lever was shifting backwards, he advanced the power lever forward as a correction. PIC applied foot brakes to control the aircraft veer and to stop the aircraft. Due to the rudder position, right brake was more effective when both foot brakes were applied.
The right foot brake tyre marks were found 72 meter from threshold at the right edge of the runway. There were no tyre marks found of left brake use. This action contributed the aircraft to veer more towards the right.
5 seconds after initiation of take-off, aircraft hit the runway fence close to the edge of the runway and swiped two security personnel who were standing on a walkway outside of the runway fence. They were walking towards tower from the helipad after welcoming high level official who arrived on helicopter 9N-ALC. One security personnel died immediately and another died while on the way to hospital airlifting by helicopter.
Aircraft hit Manang Air‘s helicopter 9N-ALC, 13 meter away from fence at upper helipad with engine running on idle power at the time of impact. Helicopter was toppled to the lower helipad 6 ft below. 9N-ALC‘s helicopter pilot was severely injured as he was trapped underneath and later rescued. The running rotor blades of 9N-ALC helicopter chopped right forward section of 9N-AMH aircraft and hit co-pilot‘s head, he died instantly at the time of accident. The LH wing of the aircraft broke the skid of helicopter 9N-ALK and came to a stop with toppled 9N-ALC beneath its RH main wheel assembly. Due to impact, 9N-ALK shifted about 8 ft laterally and suffered minor damages (few dents on the fuselage due to scattering of metal pieces during collision impact).
With respect to human factors the AAIC analysed:
According to the PIC, the co-pilot acting as PF for the flight set the power by moving the power levers forward and removed his hands from the power lever to the control column. PIC himself used to keep his hands at power lever to ensure that the power lever wouldn‘t revert, but somehow he failed to do so, on that particular flight. From FDR analysis, post-accident interview of PIC and CCTV footage, the commission found that after two seconds of initiation of take-off roll, right power lever shifted rearwards and aircraft started to veer towards right.
This article is published under license from Avherald.com. © of text by Avherald.com.
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