Preliminary report

About a month later, on 13 February, a preliminary report was released, which largely reproduced all relevant logs.

(PF = Pilot Flying, PM = Pilot Monitoring):^[45]

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) 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 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 this point, the Np of both propellers was recorded as Non-Computed Data (NCD) in the FDR and the torque (Tq) of both engines was at 0%. When propellers are in feather, they are not producing thrust [...]

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. At 10:57:20, the PM (who was previously the PF) repeated again that there was no power from the engines [...]

The aircraft's propellers had been feathered for about a minute before the crash, causing the engine to produce no thrust and lead the aircraft into a stall; the condition levers, which control the propellers, were discovered from the wreckage set to the feathered position.^{[46][lower-alpha 1]} Seconds preceding the crash, the pilots discussed a total lack of power and even moved the power lever to the extreme but failed to recognize that the condition levers were incorrectly set.^[45] That the condition levers and the flap lever are next to each other in an ATR 72, experts speculate that the monitoring pilot (Kamal KC) had inadvertently moved the former in place of the latter, when asked of by the flying pilot. While, about twenty seconds later, he would set the flap lever properly on his own, he failed to account for his previous mistake, implying that the landing checklist was not properly followed.^[46][48]

Due to the shortened final approach leg for runway 12 for this flight and another flight three days before it that landed on the same runway, the stabilization criteria for a visual approach, which is important for a safe landing, was not met at the height of 500 ft above ground level. This led the Aircraft Accident Investigation Commission to recommend the Civil Aviation Authority of Nepal (CAAN) conduct a comprehensive study for the determination of an appropriate flight path that allows a stabilized visual approach.^[45]

On 15 March, the Government of Nepal extended the deadline by 45 days to the investigation commission for the final report of the accident.^[49]

Final report

On 28 December 2023, the final report was released. It reiterated the preliminary findings that the accidental change of position of both condition levers to the feathered position resulted in the loss of thrust, leading to the aerodynamic stall and crash. Some other contributing factors are also found, mostly human errors due to a high workload, lack of appropriate technical and skill-based training, ineffective crew resource management (CRM), lack of sterile cockpit discipline, and the non-compliance with standard operating procedures (SOP).^[50][1]