Transport Transports 

Canada Canada

 TP 7245E

 

AIRWORTHINESS DIRECTIVE

The following airworthiness directive (AD) may be applicable to an aircraft which our records indicate is registered in your name. ADs are issued pursuant to Canadian 

Aviation Regulation (CAR) 521 Division X. Pursuant to CAR 605.84 and the further details of CAR Standard 625, Appendix H, the continuing airworthiness of a Canadian registered aircraft is contingent upon compliance with all applicable ADs. Failure to comply with the requirements of an AD may invalidate the flight authorization of the aircraft. 

Alternative means of compliance shall be applied for in accordance with CAR 605.84 and the above-referenced Standard. 

This AD has been issued by the Continuing Airworthiness Division (AARDG), National Aircraft Certification Branch, Transport Canada, Ottawa, telephone 613 952-4357.

Pursuant to CAR 202.51 the registered owner of a Canadian aircraft shall, within seven days, notify the Minister in writing of any change of his or her name or address. 

To request a change of address, contact the Civil Aviation Communications Centre (AARC) at Place de Ville, Ottawa, Ontario K1A 0N8, or 1-800-305-2059, or www.tc.gc.ca/civilaviation/communications/centre/ address.asp 

24-0022 (01-2005)

1/1 No.

CF-2011-40

Issue Date 

 26 October 2011 

Number: CF-2011-40 

Subject: Separation of Turbine Exhaust Duct Flanges 

Effective: 16 November 2011 

Applicability: Pratt & Whitney Canada PW901A Auxiliary Power Units, Serial Number PCE-900776

and preceding. 

Compliance: As indicated below, unless already accomplished. 

Background: The PW901A Auxiliary Power Units (APU) has experienced several events of High 

Pressure Turbine (HPT) blade fracture, some of which have resulted in the separation of 

the rear gas generator case, exhaust duct support, the turbine exhaust duct flanges and 

the release of high energy debris. Subsequent investigation revealed the turbine exhaust 

duct can separate under excessive load conditions resulting from extreme engine 

distress such as HPT blade fractures. 

In order to minimize the possibility of uncontained failure,

Pratt & Whitney Canada (P&WC) has issued Alert Service Bulletin (ASB) 16255R2 to 

strengthen the exhaust duct support in order to prevent flange separation during engine 

distress conditions. 

This directive mandates the incorporation of P&WC Service Bulletin (SB) 16255R2. 

Corrective 

Actions: 

After the effective date of this directive, the first time the APU or module is at a 

maintenance facility that can perform the modifications, regardless of the maintenance 

action or reason of APU removal, or within 42 months from the effective date of this 

directive, whichever occurs first, modify the rear gas generator case, exhaust duct 

support and the turbine exhaust duct flanges by incorporating P&WC SB 16255R2 dated 

1 March 2011, or later revisions approved by the Chief, Continuing Airworthiness, 

Transport Canada. 

Compliance with previous versions of P&WC SB A16255 prior to the effective date of this 

directive satisfies the requirements of this directive. 

Authorization: For the Minister of Transport, Infrastructure and Communities 

ORIGINAL SIGNED BY

Rémy Knoerr 

Acting Director, National Aircraft Certification 

Contact: Mr. Robin Lau, Continuing Airworthiness, Ottawa, telephone 613-952-4357, facsimile 

613-996-9178 or e-mail CAWWEBFeedback@tc.gc.ca or any Transport Canada Centre.