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.