B773, en-route, east northeast of Anchorage AK USA, 2015

B773, en-route, east northeast of Anchorage AK USA, 2015

Summary

On 30 December 2015, a Boeing 777-300 making an eastbound Pacific crossing en-route to Toronto encountered forecast moderate to severe clear air turbulence associated with a jet stream over mountainous terrain. Some passengers remained unsecured and were injured, one seriously and the flight diverted to Calgary. The Investigation found that crew action had mitigated the injury risk but that more could have been achieved. It was also found that the pilots had not been in possession of all relevant information and that failure of part of the air conditioning system during the turbulence was due to an improperly installed clamp.

Description

On 30 December 2015, a Boeing 777-300ER (C-FRAM) being operated by Air Canada on a scheduled international passenger flight from Shanghai Pudong to Toronto as ACA 088 with an augmented crew encountered a period of moderate to severe turbulence in day VMC as it crossed southern Alaska at FL 330 eight hours after take-off from Shanghai. One of the two air conditioning systems also failed. One of the 332 passengers was seriously injured and 20 others sustained minor injuries. There was some damage to cabin fittings.

The track flown and event location (a hollow circle) plotted the forecast sig weather chart. [Reproduced from the Official Report]

Investigation

An Investigation was carried out by the Canadian Transportation Safety Board. Relevant data was successfully recovered from the DFDR but since the aircraft did not land until 2 hours 45 minutes after the investigated event and the CVR continued to run, none of its data, in particular use of the cabin PA system, were of any use. It was noted that the DFDR did not record the position of the flight deck switch which is used to switch the seat belt sign on and off.

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