Air Accidents Investigation Branch
During the aircrafts approach to Belfast City Airport, a number of aircraft systems dropped off-line including some necessary for landing. The flight crew, experiencing natural effects of startle and surprise, and without a specified procedure to follow, continued with the approach, restoring systems by turning off the Transformer Rectifier Unit (TRU). The aircraft was operating under an Operations Engineering Bulletin (OEB) which required the TRU to be continually powered. Following the failure of an electrical contactor, this disconnected the DC output from the TRU to the Standby and Emergency bus bars, thereby removing electrical power to several aircraft systems.
The aircraft manufacturer has taken safety action to improve the guidance for flight crew in the event of a contactor failure when operating under the OEB. In addition, they have introduced a modification which, when embodied, removes the requirement to operate with the TRU permanently powered.
The operator intends to adopt a rule-based method for managing startle, which can help pilots manage workload and maximise their situation awareness before flying an approach.