What happened
On January 26, 2019, an Alliance Air ATR 72-600, registration VT-AIX, was performing a scheduled flight from Mumbai to Diu. The aircraft, carrying 68 passengers and 4 crew members, was on final approach to runway 05 at Diu Airport. As the aircraft descended, it encountered light turbulence and a sudden sink rate increase between 53 feet and the flare height.
This loss of airspeed, which dropped by 19 knots during the descent, led to an unstabilized approach. In an attempt to arrest the sink rate, the pilot flying applied a pitch-up input, causing the aircraft to balloon and make a momentary, heavy contact with the runway 212 meters from the threshold. The aircraft then bounced, reaching a height of approximately 6 feet. During the subsequent second touchdown, the aircraft's pitch increased to 8 degrees, causing the tail section to rub against the runway surface for 7.7 meters. Despite the impact, the aircraft remained controllable and taxied to the apron without any injuries to the passengers or crew.
The investigation
AAIB India investigators analyzed data from the Digital Flight Data Recorder (DFDR) and CCTV footage to reconstruct the landing sequence. The investigation examined the aircraft's maintenance history, the crew's qualifications, and the meteorological conditions at the time of the incident. The inquiry also reviewed the flight crew's adherence to established stabilized approach and bounce recovery procedures.
Findings
- The aircraft was fully airworthy with all maintenance and mandatory modifications up to date.
- The weather was generally good, but the local topography at Diu causes varying wind directions and seasonal thermal effects that can create downdrafts.
- The approach became unstabilized due to a sudden loss of airspeed caused by a downdraft just after the flare initiation.
- The pilot flying attempted to correct the sink rate with a pitch-up input, leading to the initial ballooning and momentary ground contact.
- The crew failed to execute a go-around despite the aircraft's unstable state and the subsequent high bounce, which exceeded the five-foot threshold defined in the manufacturer's recovery techniques.
- The pilot monitoring did not call for a go-around during the unstable phase or the significant bounce.
Safety action
- The operator is advised to integrate proper go-around procedures for unstabilized approaches and specific bounce recovery techniques into their training programs.
- The operator should emphasize the correct execution of ATR-specific bounce recovery techniques during all ground refresher and simulator training sessions.