Aviation safety issues and actions
Safety Advisory Notice issued to: Operators and flight crews of transport category aircraft
|Date issued:||13 December 2010|
|Safety action status:||Closed|
|Background:||Why this Safety Advisory Notice was developed|
The priority level of the battery discharge messages that were provided by the engine indicating and crew alerting system did not accurately reflect the risk presented by the battery discharge status.
Action taken by the ATSB
During the investigation, the ATSB discussed the background for this safety issue and the associated safety risk with the aircraft manufacturer. The potential for a reduction in the associated risk to as low as reasonably practicable by proactive manufacturer safety action was highlighted.
Action taken by the aircraft manufacturer
On 29 October 2010 the aircraft manufacturer reported that it had 'reviewed the priority level of the BAT DISCH message that is provided by the EICAS and finds that the current message level "Advisory" is correct.' The aircraft manufacturer provided the following justification:
[The aircraft manufacturer] believes that the "Advisory" level is correct since an advisory level message typically means that routine crew awareness and corrective action may be required. There is no flight crew action for BAT DISCH MAIN and BAT DISCH APU, these messages only note that the corresponding batteries are discharging when/if electrical loads is sufficient to generate battery drain and the battery is not charging. This situation can occur whenever AC electrical bus 1 is lost, due to the fact the battery chargers are powered by this bus by the way of the ground service bus.
A more important crew alert in a multiple bus loss event, like this investigation, is the EICAS Caution message ELEC AC BUS (X). These messages direct flight crews to the appropriate procedures to attempt to restore electrical power.
ATSB assessment of action
The ATSB recognises that any change in the priority level of the battery discharge messages would contradict the EICAS priority level definitions if no crew actions were associated with the message entries in the QRH. Accordingly, the priority level and QRH should be assessed concurrently. However, the risk presented by the potential for the battery discharge message to be overlooked in the event of multiple EICAS messages remains significant.
Safety Advisory Notice
The ATSB reminds operators and flight crews of transport category aircraft that although battery discharge may occur routinely, immediate flight crew action may be necessary in the event of abnormal or unexpected battery discharge alerts if the battery discharge status cannot be immediately resolved in-flight. Multiple electrical system failures, including failures of critical flight systems, may occur in the event of battery power depletion.