What happened
On July 4, 2019, a Vistara Airlines A-320, registration VT-TTN, was operating a flight from Srinagar to Jammu when it encountered significant weather disturbances. While en route, the aircraft encountered heavy convective activity near MESAR, necessitating a deviation from its planned track. Upon approaching Jammu, the crew encountered intense wind gradients and heavy cloud cover, prompting them to abandon the approach to Jammu.
Due to the presence of large cumulonimbus cells and a hailstorm warning at the departure airport, the crew decided to divert to Amritsar. During the diversion, the aircraft had to navigate around extensive weather systems, which required several altitude changes and lateral deviations. As the flight progressed, the crew observed a drop in fuel levels, eventually triggering an ECAM low-pressure fuel pump warning. The aircraft declared a "Mayday Fuel" status to Amritsar ATC and landed with only 460 kg of fuel remaining on board.
The investigation
The AAIB India investigation focused on the fuel planning, weather awareness, and the decision-making processes of the flight crew and the operator. Investigators examined the transit briefing provided at Srinagar, which indicated that while the flight plan listed Amritsar as the sole alternate, the briefing sheet included Delhi as a second alternate. However, the fuel uplifted did not account for the requirements of this second alternate.
Technical analysis of the flight records and cockpit communications revealed that the crew did not utilize the most recent meteorological data for the destination. Furthermore, the investigation looked into the organizational pressures regarding "suitable alternates" and the lack of proactive weather monitoring by the airline's operations center. The investigation also scrutinized the impact of air traffic control instructions, such as step climbs, on the aircraft's fuel depletion during the diversion.
Findings
- The primary cause of the incident was the failure to uplift sufficient fuel to account for a second alternate airport, especially given the lack of recent weather updates for the destination.
- The flight crew did not request the most recent METAR or satellite imagery for Jammu prior to departure.
- There was a lack of situational awareness regarding the developing weather patterns near the diversion airport, which led to unplanned fuel consumption.
- Ambiguities in company documentation and regulatory requirements regarding "suitable" versus "adequate" alternates contributed to the crew's decision-making.
- The crew did not declare "Minimum Fuel" to ATC early enough, and subsequent ATC clearances contributed to further fuel exhaustion.
Safety action
- The DGCA has been advised to instruct operators to carry enough fuel to reach a second alternate when recent weather data is unavailable.
- Recommendations were made to clarify the distinction between "suitable" and "adequate" alternates to empower pilots to divert to the nearest safe airport.
- The investigation highlighted the need for flight dispatchers to proactively provide fuel planning that accounts for the second alternate in cases of weather uncertainty.
- There is a recommendation to revise regulatory frameworks to remove ambiguities regarding discretionary fuel and holding requirements during periods of air traffic congestion.