What happened
On 20 October 2018, an Air India Boeing 787-8, registration VT-ANE, was conducting a commercial passenger flight from Indira Gandhi International Airport to Hong Kong International Airport. Prior to arrival, the crew had been briefed on the potential for Instrument Landing System (ILS) glideslope fluctuations due to single runway operations at Hong Kong. Air Traffic Control also specifically warned the crew of possible signal interference caused by an aircraft within the sensitive area of the glide path.
During the ILS approach to Runway 07R, the aircraft underwent a rapid descent. This deviation triggered several alerts from the Ground Proximity Warning System (GPWS). The crew initiated a go-around when the aircraft reached a radio altitude of 280 feet, approximately 2.6 nautical miles from the runway. The aircraft subsequently completed a successful landing on its second approach. There were no injuries to the 197 passengers or 10 crew members on board.
The investigation
The investigation examined the flight path, the functionality of the aircraft's navigation systems, and the operational environment at Hong Kong International Airport. Investigators analyzed the impact of single runway operations on the stability of the ILS signal and reviewed the crew's adherence to stabilized approach criteria. The investigation also looked into human factors, including the impact of the 'startle effect' and the crew's management of the known signal fluctuations.
Findings
- The primary cause of the deviation was glideslope signal interference caused by an aircraft positioned within the sensitive area of the ILS glide path.
- The crew was aware of the potential for signal fluctuations via ATIS and ATC communications, but the sudden nature of the descent contributed to task saturation.
- The crew's decision to execute a go-around was appropriate given the rapid loss of altitude.
- Factors such as the startle effect and the workload during the approach influenced the crew's response to the signal disturbance.
Safety action
- The investigation recommended that Air India review its Crew Resource Management (CRM) training to address potential authority gradients and ensure crew members feel empowered to follow standard operating procedures and take control of the aircraft during emergencies without fear of retribution.