Summary
We propose to adopt a new airworthiness directive (AD) for the products listed above that would supersede an existing AD. This proposed AD results from mandatory continuing airworthiness information (MCAI) originated by an aviation authority of another country to identify and correct an unsafe condition on an aviation product. The MCAI describes the unsafe condition as: Uncontained APU [auxiliary power unit] generator failures on ground have occurred on Airbus A330 aircraft in service. APU generator design is common to all A330 and A340 aircraft. Preliminary investigations confirmed that these failures have resulted in structural damage to the APU compartment and, in one case, to the stabiliser compartment. Loose APU generator parts can lead to damage to the APU firewall, reducing its fire extinguishing capability and potentially leading to a temporary uncontrolled fire.
Although the root cause has not yet been determined, the investigation showed a sequence of events where a collapse of the Drive End Bearing (DEB) leads to an uncontained failure. Evidence has also shown that the DEB failures are not instantaneous, and therefore, the detection of small debris could indicate early stage of a DEB failure.
The proposed AD would require actions that are intended to address the unsafe condition described in the MCAI.