FAA AD 2012-18-14 Pratt & Whitney
(a) Effective Date:This airworthiness directive (AD) becomes effective October 22, 2012.
(b) Affected ADs:None.
(c) Applicability: This AD applies to Pratt & Whitney Canada (P&WC) PW901A auxiliary power units (APUs) approved under Technical Standard Order TSO-C77A and installed on, but not limited to, Boeing 747-400 series airplanes. The affected APU serial numbers are PCE 900001 through PCE 900776 inclusive.
(d) Reason :This AD was prompted by several events of high-pressure turbine blade fracture leading to separation of the rear gas generator case and release of high energy debris. We are issuing this AD to prevent separation of the rear gas generator case and release of high energy debris, which could result in injury and damage to the airplane.
(e) Actions and Compliance Unless already done, do the following actions.
(1) Within 42 months after the effective date of this AD or the first time the APU or module is at
a maintenance facility that can perform the modifications, regardless of the maintenance action or reason for APU removal, whichever occurs first, modify the rear gas generator case, exhaust duct support, and turbine exhaust duct flanges.
(2) Use paragraphs 3.A. through 3.B(3)(f) of Accomplishment Instructions, and paragraph 4.A.
of Appendix, of P&WC Alert Service Bulletin (SB) No. 39100001-49-A16255, Revision No. 2, dated March 1, 2011, to do the modifications.
(f) Credit for Previous Action: APUs modified before the effective date of this AD using P&WC Alert SB No. A16255R1, dated September 12, 2008, or P&WC Alert SB No. A16255, dated December 12, 2007, meet themodification requirements of this AD.
S P Singh