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Summary

Summary

On 5 December 2001, a Saab 340B registered VH-XDZ departed Trepell Qld, at 0810 EST with 37 persons on board. The flight was planned in accordance with instrument flight rules (IFR) to Townsville Qld, via Richmond Qld, at Flight Level (FL) 190.

While on climb through FL180, the copilot's two electronic flight information system (EFIS) screens on the right side of the aircraft's instrument panel failed. After the crew had consulted the EFIS failure/disturbances checklist, the central warning panel ice protection annunciator and then the cabin pressure annunciator illuminated. An emergency descentwas initiated and the crew broadcast a PAN call to Air Traffic Services (ATS) and reported that they were returning to Trepell.

During the descent a number of other cockpit warnings and cautions activated and some aircraft systems failed. The crew became aware that the right DC generation system wasoperating abnormally. Their attempts to rectify that situation were unsuccessful. The crew diverted the aircraft to Cloncurry and landed.

The failure of the EFIS screens and the subsequent warnings, cautions and failures were consistent with a right system voltage drop from the rated 28 volts DC to below 18 volts. During the investigation it became apparent that in some Saab 340 aircraft a startergenerator could fail without taking the generator off line and alerting the crew, resulting inlow system voltage. On this occasion the crew overlooked the first item of the EFISfailure/disturbances checklist, which required a check of the generator voltage. Consequently, the crew did not recognise the developing low voltage condition that led to the cascading series of warnings, cautions and failures. The bus tie relay, which was designed to automatically connect the two main electrical systems in the case of generator failure, did not operate. An optional generator control unit modification, to preventunalerted low-voltage conditions, had not been incorporated. The investigation determined that the modification to reduce the risk of the consequences of a delayedgenerator failure warning was highly desirable.

The investigation found that the operator's maintenance control system and approved system of maintenance did not ensure that the starter generator was maintained in accordance with the requirements of the aircraft maintenance review board (MRB) report. A contributing factor was the disparity between a MRB requirement and the corresponding job card produced by the aircraft manufacturer.

This occurrence also demonstrates the need for well-designed checklists to be available to pilots during abnormal or emergency situations. It further demonstrates the need for pilots to be familiar with the systems of the aircraft they operate and the actions to be taken in the event of abnormal or emergency situations. As a result of this occurrence the ATSB hasissued a number of recommendations to address safety concerns identified during theinvestigation.

 
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