AD NUMBER: 2008-20-04
MANUFACTURER: Rolls Royce
SUBJECT: Airworthiness Directive 2008-20-04
SUMMARY: We are adopting a new airworthiness directive (AD) for the products listed above.

This AD results from mandatory continuing airworthiness information (MCAI) issued 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: High pressure (HP) turbine discs recently inspected inaccordance with the Engine Manual have exhibited cracks in the disc rim.

The discs have failed to meet the inspection acceptance criteria and have been returned to Rolls-Royce for engineering investigation. This investigation has concluded that the cracks have resulted from scores within the cooling air holes in the disc rim that could have been introduced during new part manufacture or during overhaul of the disc.

The engineering investigation has concluded that if this cracking was undetected then it could result in uncontained disc failure and a potential unsafe condition for the aircraft. We are issuing this AD to prevent uncontained disc failure, possibly resulting in damage to the airplane.

FMI: www.faa.gov/regulations_policies/airworthiness_directives/