Yeti Airlines DHC6 at Lukla, on October 8th, 2008, crashed on runway
Last Update: February 22, 2017 / 15:08:36 GMT/Zulu time
The primary cause was the flight crew's misjudgement, based on the weather information from all the preceding aircraft and Lukla Information, to enter into cloud patch on final wherein the aircraft encountered the rapidly uplifting fog on short final resulting in control flight into terrain.
Probable contributing factors have been:
- failure on the part of the regulatory body and company safety management to check the wrong practices being followed by pilots especially in STOL airfields like Lukla on a timely basis.
- AFIS personnel on duty not being able to declare airport closure due to high workload, stress and landing of three prededing aircraft in similar marginal weather conditions.
- Operator's priority of economical aspect over safety such as their unequal treatment between pilots landing in adverse weather and diverters, creating a 'Must Land' situation.
The captain (41, ATPL, 8,185 hours total, 7,180 hours on type) was pilot flying, the first officer (28, CPL, 556 hours total, 341 hours on type) was pilot monitoring.
The aircraft was equipped with GPS receivers. As Lukla AFIS did not provide a QNH the crew continued to use the QNH setting provided by Kathmandu Tower.
The flight from Kathmandu towards Lukla was uneventful, weather information prior to departure from Kathmandu had indicated visibility of 5000 meters, overcast cloud at 2000 feet and scattered cloud below. At 01:43Z the aircraft entered the Lukla Valley at 8500 feet MSL, at that time another aircraft (9N-AHE) was lining up for departure from Lukla and after departure reported that cloud were at 9000 feet and had reached the runway (aerodrome elevation 9100 feet). At 01:44:29Z 9N-AHE reported passing 9N-AFE.
At 01:45:05Z the captain queried Lukla Information whether the runway threshold could be seen, Lukla AFIS replied "affirm, Sir, affirm". Just before entering the cloud the captain asked whether final was fine, Lukla AFIS replied "affirm, sir, affirm, visible".
The NAIC reported that this reply cast doubt on the pilot report by 9N-AHE, due to the workload increasing by deteriorating weather, conflicting traffic, searching the runway and the psychological pressure that three other aircraft had landed tunnel vision to continue the approach and land was created.
The captain confirmed with the first officer that they were lined up straight on final track, then the aircraft entered the uplifting fog. Unknown to the captain the fog was rapidly reaching the runway threshold covering the final approach and threshold area. The first officer raised his doubt in a soft voice asking whether the captain could see the final.
At 01:46Z the aircraft impacted ground 50 meters ahead of the runway threshold and 48 feet below the runway threshold and came to a rest 20 meters before the runway threshold and 15 feet below the threshold level. Both pilot seats including the pilots were catapulted out of the cockpit and landed in the threshold area. The aircraft caught fire. Both pilots were recovered alive, the first officer succumbed to his injuries, caused by internal head injuries caused by impact with the aerodrome perimeter fence, while being transported from the threshold to the airport buildings. The captain survived with serious injuries including fracture of lumbar vertebrae disabling the captain to walk. The other occupants received serious impact injuries causing death, the bodies subsequently received burn damage.
The NAIC reported the aircraft was equipped with a cockpit voice recorder, a flight data recorder was not required and was not present.
The NAIC reported that in interviews with the airline staff it became obvious that there had been no meeting between safety management or operations and pilots for a prolonged period of time and the operator lacked a non-punitive reporting system. There was hidden pressure, especially during peak tourist season and marginal weather conditions, to accomplish the flights.
The NAIC reported that there were mandatory visits to cockpit resource management courses every year. However, data of previous accidents showed that the first officers did not raise their voices over questionable decisions by the pilot in command.
The NAIC reported that CAA Nepal had reported lack of technical staff, which resulted in difficulties to perform regulatory oversight.
The NAIC analysed that there was no technical malfunction contributing to the accident. The pilots were not under the influence of alcohol or drugs, were not incapacitated, there was no evidence of unlawful interference or explosives. The aircraft was loaded within permitted limits, the center of gravity was within permitted limits.
The NAIC analysed that the first aircraft, 9N-AFA, had arrived in Lukla at 01:33z and departed Lukla at 01:39z. The next aircraft was 9N-AHE, who on approach to Lukla provided pilot reports indicating that it was probably not possible to land in Lukla, however, made it to a landing (and subsequent departure). The NAIC wrote: "9N-AHE repeatedly informed others about deteriorating weather, whereas he himself was able to continue and land. This may have created doubt on other pilots behind him regarding his pilot reports." The third aircraft to land was 9N-AET, who advised it was necessary to descend to 8000 feet to enter the valley, the base was covered up and status of final was unknown, he would advise upon reaching final. 9N-AFE was behind 9N-AET.
About 2nm out 9N-AFE queried 9N-AFA, who had departed again, 9N-AFA reported final was fine, patch of cloud was on long final and they might be able to make it into Lukla. The weather in the valley was fine with ample of room for overshoot.
At 01:42z the crew of 9N-AFE read their final landing checklists, were told 9N-AET was on the ground which further re-affirmed their belief the patch of cloud was on long final only.
With that information and Lukla AFIS answering "affirm" to whether the final was fine/threshold visible the crew hoped the cloud was on long final only and they would be visible with the runway on short final.
This article is published under license from Avherald.com. © of text by Avherald.com.
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