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Final Report

Summary

What happened

On 21 December 2015, a Boeing 787-8 aircraft, registered VH-VKE, departed Melbourne, Australia on a scheduled passenger transport service to Singapore. Approximately 4 hours into the flight, just north of Australia, the airspeed indications became erratic. As a result, the autopilot disconnected and the Primary Flight Control reverted to a mode with fewer automated functions and protections. After approximately 17 seconds the airspeed values returned to normal.

Due to the latching nature of the Primary Flight Control mode reversion, the aircraft had to be manually flown for the remainder of the flight and because of this, the crew diverted the aircraft and made an uneventful landing in Darwin, Australia.

What the ATSB found

The ATSB found that the aircraft had entered an area of weather with high ice water content, which caused the pitot-static systems to become affected by ice. The flight control logic detected a resulting drop in airspeed, sufficient to revert to secondary mode.

What has been done as a result

Boeing revised the flight control software to reduce the chances of reverting to secondary mode in a short duration, erratic airspeed event.

In response to a previous, similar event on another B787-8, the FAA published an airworthiness directive warning flight crew not to make large abrupt magnitude flight control inputs in response to unrealistic drops in airspeed.

Boeing also revised the flight control software to limit the rate of elevator feel reduction with drops in airspeed. This will specifically allow the column to stay at a higher feel force to mitigate large and abrupt unintentional pitch inputs.

Safety message

In this case, the crew showed a high level of professionalism in response to a weather related event. The crew demonstrated high levels of communication and coordination, promptly applied checklists and procedures.

The ATSB brings to the attention of all flight crews, the importance of following documented procedures and directives when encountering weather related events.

The occurrence

Safety analysis

Findings

Sources and submissions

 
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