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Maintenance processes for corrosion in the generator control units

Issue number: AO-2008-003-SI-03
Who it affects: Operators of aircraft fitted with Hamilton Sundstrand Corporation generator or bus control units
Issue owner: Hamilton Sundstrand Corporation
Operation affected: Aviation: Maintenance
Background: Investigation Report AO-2008-003
Date: 13 December 2010

Safety issue description

Maintenance processes did not identify or correct the corrosion in the generator control units.

Proactive Action

Action organisation: Hamilton Sundstrand Corporation
Action number: AO-2008-003-NSA-034
Date: 13 December 2010
Action status: Closed

The GCU/BCU manufacturer implemented procedures for a more thorough inspection of the external chassis of GCUs and BCUs received for repair for signs of liquid contamination, and a circuit card removal and inspection for any suspect units.

The GCU/BCU manufacturer drafted a service information letter to operators and maintenance providers advising that: Unexplained EICAS [engine indicating and crew alerting system] messages and aircraft electrical system anomalies may result from the presence of corrosion and contamination within the GCU or BCU circuitry. Operators suspecting water ingress of the GCU or BCU should remove the units to an avionics repair shop and request a physical inspection and a careful cleaning of the Printed Wiring Assemblies [PWA], the motherboard, and all interconnections to ensure contamination of the circuitry is not present. A test validation is not sufficient to detect corrosion and contamination of the internal circuitry. Avionic repair stations should examine the NVM [non-volatile memory] of each unit and perform a visual examination of PWAs for corrosion and contamination.

ATSB response:

The ATSB is satisfied that the actions taken and proposed by the GCU/BCU manufacturer adequately address the safety issue.

Proactive Action

Action organisation: Qantas Airways
Action number: AO-2008-003-NSA-035
Date: 13 December 2010
Action status: Closed

The aircraft operator:

  • now requires all overhauled GCUs and BCUs to be internally inspected for corrosion, and the environmental protection inspected and reapplied as required in accordance with the manufacturer’s standard practices
  • conducted a review of tech log reports on their 747-400 fleet to determine if specific AC power buses exhibit repeated intermittent failures or symptoms that may be attributable to internal corrosion or contamination
  • is undergoing a scheduled removal of all BCUs and GCUs fitted to 747-400 aircraft to inspect internally for corrosion and environmental protection - this is being performed initially for aircraft that exhibit symptoms on AC bus 3.

ATSB response:

The ATSB is satisfied that the actions taken and proposed by the aircraft operator adequately address the safety issue.

   
Current issue status: Adequately addressed
Status justification:

The ATSB is satisfied that the actions taken adequately address the safety issue.

 
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Last update 07 March 2014