Investigators with the Aircraft Accident Investigation Commission of Nepal released their preliminary report on the crash of Yeti Airlines flight 691 this week. The report details the sequence of events that led to the crash based on data from the Flight Data Recorder and Cockpit Voice Recorder. The full report is available for download here.
Two captains flying
Yeti flight 691 was the third flight of the day for the flight crew, which consisted of two captains. They had flown one round trip between Kathmandu and Pokhara before the accident flight. On Yeti 691 the pilot flying (PF) was the captain undergoing familiarization for landing in Pokhara, while the pilot monitoring (PM) was acting as the instructor pilot.
Yeti flight 691 sequence of events
The take off, climb, cruise, and initial descent from Kathmandu to Pokhara was uneventful. As the pilots prepared for landing at 10:56:12 (UTC +5:45), they selected flaps 15 and lowered the landing gear.
15 seconds after extending the flaps, the PF disengaged the autopilot at 721 feet above ground level.
The PF then called for “FLAPS 30” at 10:56:32, and the PM replied, “Flaps 30 and descending”. 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.
The ATR 72 center column
Based on the Nepalese investigator’s preliminary report it appears the PM (right seat) moved the prop levels to feather (FTR) instead of moving the flaps level to 30 at this point.
At 10:56:54 after descending below 500 AGL one of the pilots moved the flaps to the 30 degrees position.
Through the rest of the flight, the pilots noted that there was no power coming from the engines, while the aircraft descended. The stick shaker was activated twice, the final time at 10:57:26 and the aircraft “banked towards the left abruptly.” Consistent with the last available ADS-B data received, the FDR and CVR stopped recording at 10:57 local time (5:12 UTC).
What is the focus of the investigation now?
The continuing investigation will focus on three factors:
- The circumstances under which both propellers went into the feathered condition
- Human factors
- Visual approach procedures into Pokhara International Airport, including simultaneous operation of both national and international airports.
The final point relates to the approach procedures put in place following the recent opening of the new international airport, which is located close to the old airport.
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