What happened
On October 18, 2011, a Boeing 777-300, registration A6-ETC, was operating a scheduled passenger service from Manila, Philippines, to Abu Dhabi, UAE. While traversing the Bay of Bengal at flight level 340, the aircraft encountered a region of severe turbulence for approximately 45 seconds.
Prior to the event, the crew had identified an isolated cumulonimbus cell on the weather radar directly in their flight path. In an attempt to avoid the convective activity, the crew executed a lateral deviation from the original track. During this maneuver, the aircraft experienced intense vertical accelerations, causing the autopilot to disconnect and the aircraft to climb roughly 6/00 feet. The encounter resulted in one serious injury to a passenger and one serious injury to a cabin crew member, along with several minor injuries to others.
The investigation
An investigation by the GCAA AAIS examined the flight profile, crew performance, and aircraft systems. Investigators analyzed digital flight data and the cockpit voice recorder, though they noted that the CVR was not recording on four separate channels as required by regulations. The inquiry also looked into the crew's management of the weather radar and communication systems, specifically the CPDLC and radio handovers between the Yangon and Kolkata Flight Information Regions.
Findings
Several contributing factors were identified that led to the late deviation from the flight path. The investigation found that the late recognition of adverse weather was exacerbated by several issues:
- The Captain was not on the flight deck at the time of the encounter, which impacted the crew resource management environment.
- The remaining crew faced distracting and contradictory radio communications during a regional airspace handover.
- There were difficulties with high-frequency communications and delays in CPDLC data link updates.
- The crew demonstrated unfamiliarity with certain weather radar and data link procedures.
Additionally, the investigation found that cabin crew were performing routine duties rather than securing themselves during the period when the seat belt sign was active. The investigation also noted that the use of lavatories was not sufficiently restricted during the period of turbulence, contributing to the injuries sustained.