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Turkish Airlines has made six changes to its processes and procedures following the March 4 excursion by an Airbus A330-300 landing at the Tribhuvan airport in Kathmandu, Nepal after a flawed non-precision instrument approach in fog and deteriorating visibility.
According to a final report by the Nepalese accident investigation commission (AIC), the probable cause for the non-fatal incident that left the A330 substantially damaged was the pilots’ decision to continue the required navigation performance (RNP) approach well below the minimum descent altitude without seeing the runway environment.
In that situation, standard procedures call for the crew to immediately execute a missed approach at the minimum altitude, a procedure the pilots had correctly followed on the first approach to the airport that morning.
On the second approach, the pilots claimed to have seen the runway at the required point, but then lost sight of it later, which would also require an immediate go-around. Based on the cockpit voice recorder, the AIC concluded however that the pilots did not have the required visual references and continued the approach regardless, in part due to a “fixation” to land as weather was deteriorating. Witnesses on the ground stated the visibility was “zero.”
Turkish had begun using the RNP authorization required approach to Runway 2 at the end of 2014, and both pilots were trained on the procedures in the simulators around that timeframe. However the incident flight was the captain’s first to Kathmandu and the first officer’s first RNP approach in actual conditions.
According to the flight data recorder, the autopilot system remained connected until 14 ft. above the ground, well below the 340 ft. minimum descent altitude, whereupon the captain attempted to raise the nose, or flare, for a normal landing. The flare amount was insufficient however and the aircraft’s gear hit with a force of 2. 7G, offset well to the left side of the runway. The aircraft came to a stop on the left side of the runway. The passengers and crew evacuated with no “significant” injuries.
The AIC determined that the aircraft was offset 85 ft. to the left of centerline due to a navigation database error that the airline had not discovered despite a similar report by a crew that landed at the airport two days earlier.
Of the 21 safety recommendations issued, nine were directed at Turkish, including a review of pilot qualifications and strictly following approach procedures; 11 were sent to the civil aviation authority of Nepal and the airport’s weather provider, and one was directed to Lido, Turkish’s chart provider.
Turkish voluntarily made six upgrades after the incident, including requiring three pilots for Kathmandu approaches, doubling the required minimum visibility to start an approach to 1 nm from 0.5 nm, setting up a quality control unit to review charts, and developing new procedures to check the validity of flight management system databases.