Description

On 15 January 2023, an ATR 72-500 (9N-ANC) being operated by Yeti Airlines on a scheduled domestic passenger flight from Kathmandu to Pokhara International as NYT691 was about to turn onto a visual final approach for runway 12 at destination in day VMC when it was observed to suddenly depart normal flight and descend rapidly and impact uninhabited terrain. The impact completely destroyed the aircraft and all 68 passengers and the four crew members on board were killed.

Investigation

An Aircraft Accident Investigation Commission was established on the day of the accident in accordance with the Civil Aviation (Accident Investigation) Regulation (2016) of Nepal. The CVR and FDR were both recovered from the accident site and their data were successfully downloaded under supervision by the Singapore Transport Safety Investigation Bureau (TSIB). 

It was found that the accident flight was being used for familiarisation training of the 44 year-old PF Captain in respect of the recently opened (1 January 2023) new airport at Pokhara and that a 58 year-old Training Captain had been in command of the flight and occupying the right hand seat. The accident sector was their third flight of the day and had been preceded by a Kathmandu-Pokhara-Kathmandu rotation.

Recorded flight data showed that the flight proceeded normally until the approach phase. ATC initially assigned 2,500 metre-long runway 30 for a straight-in landing but the crew subsequently requested and received clearance to use the equivalent-length runway 12 instead which the prevailing light and variable reported surface wind favoured. 

Five minutes after beginning descent from just under 4000 feet aal when five miles north of the airport whilst tracking towards a left base leg position, flap 15 was set and the landing gear selected down. The AP was then disengaged at a recorded 721 feet agl and the PF called for Flaps 30 and received the response “flaps 30 and descending”. However no flap surface movement was recorded on the FDR at that time and “instead” the propeller rotation speed (Np) of both engines “simultaneously decreased to less than 25%". The recorded torque began to reduce towards zero which would be expected as both propellers feathered.

The CVR area microphone recorded a single Master Caution annunciation four seconds after the propeller feathering had begun. The ‘Before Landing’ Checklist was then completed followed by the left turn onto base leg. During that time, the Power Lever Angle (PLA) increased slightly from 41% to 44%. At that point, both FDR Np indications defaulted to ‘Non-Computed Data’ (in accordance with the 25% lower threshold for Np recording) and both engine torques had reached zero (when propellers are in feather, no thrust is produced). There was no evidence in the FDR data of any engine-related anomaly. 

Eighteen seconds after the flap 30 call had been followed by propeller feathering, the 500 feet agl call was recorded on the CVR during the turn onto left base. The PF was recorded asking the PM “whether to continue the left turn” and was advised to do so. He then asked whether the descent should be continued and the PM responded by saying this was not necessary but instructed the PF to “apply a little power”. Only after this exchange were the flaps recorded as moving from 15° to the previously requested 30°.

Ten seconds later, with the aircraft still on left base leg, TWR gave a landing clearance and the PF “mentioned twice that there was no power coming from the engines”. The Power Levers were advanced initially to 62° PLA and then to maximum and soon afterwards the left turn onto final approach was commenced at a recorded 368 feet agl. Seven seconds after this, the PF passes control to the Training Captain and followed this by repeating that “there was no power from the engines” despite the increase in PLA. Four seconds after this, at a recorded 311 feet agl, a stick shaker activation began and the aircraft banked “abruptly” left and descended rapidly into the terrain below with impact eight seconds after the stick shaker had begun.

A post crash fire began and the wreckage was subsequently located in one of the few unpopulated areas, the gorge of the Seti Gandaki River which resulted in no damage to ground structures or injuries to persons on the ground.   

The location of the accident site in relation to the new and old airports. [Reproduced from the Official Report]

It was noted from FDR data that, the flight path of the accident approach and that of another visual approach to the same runway at the new Pokhara airport three days earlier by a different crew, “due to the shortened final approach leg for runway 12” neither of these approaches had met the normal requirement for a visual approach to be stabilised at and below 500 feet agl.

One Interim Safety Recommendation was issued as a result of the initial findings of the Investigation as follows:

• that the Civil Aviation Authority of Nepal (CAAN) should conduct a comprehensive study to determine the appropriate flight path that allows the criteria for a stabilised visual approach to be met, taking into consideration the simultaneous operations at both Pokhara airports, before resuming a visual approach to Runway 12 at Pokhara International. 

A Preliminary Report on initial progress with the Investigation on which this summary is based was completed on 13 February 2023.

Related Articles

• Loss of Control
• Feathering
• Stall
• Stabilised Approach
• Visual Approach