Yeti airlines flight YT691 crashed on 15 January 2023, operated with an ATR 72-212A as scheduled flights between Kathmandu (VNKT) and Pokhara International Airport (VNPR).
The same flight crew operated two sectors between VNKT to VNPR and VNPR to VNKT earlier in the morning.
The Yeti airlines flight YT691 accident occurred during a visual approach for runway 12 at VNPR.
This was the third flight by the crew members on that day. The flight was operated by two Captains, one Captain was in the process of obtaining aerodrome familarization for operating into Pokhara and the other Captain being the instructor pilot. The Captain being familarized, who was occupying the left hand seat, was the Pilot Flying (PF) and the instructor pilot, occupying the right hand seat, was the Pilot Monitoring (PM).
At 10:56:27, the PF disengaged the Autopilot System (AP) at an altitude of 721 feet Above Ground Level (AGL).
The PF then called for “FLAPS 30” at 10:56:32, and the PM replied, “Flaps 30 and descending”.
The flight data recorder (FDR) of Yeti airlines flight YT691 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.
On the cockpit voice recorder (CVR) area microphone recording, a single Master Caution chime was recorded at 10:56:36. The flight crew then carried out the “Before Landing Checklist” before starting the left turn onto the base leg. During that time, the power lever angle increased from 41% to 44%. At the point, Np of both propellers were recorded as Non-Computed Data (NCD) in the FDR and the torque (Tq) of both engines were at 0%. When propellers are in feather, they are not producing thrust.
When both propellers were feathered, the investigation team observed that both engines of 9N-ANC were running flight idle condition during the event flight to prevent over torque. As per the FDR data, all the recorded parameters related to engines did not show any anomaly.
At 10:56:50 when the radio altitude callout for five hundred feet was annunciated, another “click” sound was heard.
The aircraft reached a maximum bank angle of 30 degrees at this altitude. The recorded Np and Tq data remained invalid. The yaw damper disconnected four seconds later. The PF consulted the PM on whether to continue the left turn and the PM replied to continue the turn. Subsequently, the PF asked the PM on whether to continue descend and the PM responded it was not necessary and instructed to apply a little power. At 10:56:54, another click was heard, followed by the flaps surface movement to the 30 degrees position.
When ATC gave the clearance for landing at 10:57:07, the PF mentioned twice that there was no power coming from the engines.
At 10:57:11, the power levers were advanced first to 62 degrees then to the maximum power position. It was followed by a “click” sound at 10:57:16.
One second after the “click” sound, the aircraft was at the initiation of its last turn at 368 feet AGL, the high-pressure turbine speed (Nh) of both engines increased from 73% to 77%.
It is noted that the PF handed over control of the aircraft to the PM at 10:57:18.
At 10:57:20, the PM (who was previously the PF) repeated again that there was no power from the engines. At 10:57:24 when the aircraft was at 311 feet AGL, the stick shaker was activated warning the crew that the aircraft Angle of Attack (AoA) increased up to the stick shaker threshold.
At 10:57:26, a second sequence of stick shaker warning was activated when the aircraft banked towards the left abruptly. Thereafter, the radio altitude alert for two hundred feet was annunciated, and the cricket sound and stick shaker ceased. At 10:57:32, sound of impact was heard in the CVR. The FDR and CVR stopped recording at 10:57:33 and 10:57:35 respectively.
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