AD 91-24-03 ACTIVE

91-24-03 PRATT & WHITNEY CANADA: Amendment 39-8088. Docket No. 91-ANE-36. Supersedes AD 90-24-05, Amendment 39-6812.
Applicability: Pratt & Whitney Canada (PWC) PW123, PW124B, PW125B, and PW126A turboprop engines installed on but not limited to DeHavilland Dash 8 Series 300, Aerospatiale ATR72, Fokker 50, and British Aerospace ATP aircraft.
Compliance: Required as indicated, unless accomplished previously.
To prevent a low pressure turbine (LPT) overspeed, that could result in uncontained disk failure, and subsequent damage to the aircraft, accomplish the following:
(a) For PW123 and PW124B engines that have not been modified in accordance with any revision level of PWC Service Bulletin (SB) 21018, prior to the effective date of this AD, accomplish the following:
(1) Within 5 days after the effective date of this AD, perform a turbomachinery magnetic chip detector (MCD) continuity check in accordance with PWC SB 20938, Revision 2, dated November 18, 1991.
(2) Within 5 days after the effective date of this AD, perform a turbomachinery MCD functional check in accordance with PWC SB 20938, Revision 2, dated November 18, 1991.
(3) Thereafter, at intervals not to exceed 25 flight hours since last inspection, perform the turbomachinery MCD continuity check specified in paragraph (a)(1) of this AD.
(4) Thereafter, at intervals not to exceed 300 flight hours since last inspection, perform the turbomachinery MCD functional check specified in paragraph (a)(2) of this AD.
(b) In addition to the requirements of paragraph (a) of this AD, for PW123 engines that have not been modified in accordance with any revision level of PWC SB 21018, prior to the effective date of this AD, accomplish the following:
(1) Within 5 days after the effective date of this AD, perform a turbomachinery MCD airframe circuitry check in accordance with PWC SB 20938, Revision 2, dated November 18, 1991.
(2) Thereafter, at intervals not to exceed 300 flight hourssince last inspection, perform the turbomachinery MCD airframe circuitry check specified in paragraph (b)(1) of this AD.
(c) For PW125B and PW126A engines that have not been modified in accordance with any revision level of PWC SB 21018, prior to the effective date of this AD, accomplish the following:
(1) Within the next 125 flight hours after the effective date of this AD, unless previously accomplished within the last 875 flight hours, perform a turbomachinery MCD operational check in accordance with the applicable engine maintenance manual.
NOTE: Further information on the turbomachinery MCD operational check specified in paragraph (c)(1) can be found in PWC Maintenance Manual Part Number 3034932 for the PW125B, and PWC Maintenance Manual Part Number 3034922 for the PW126A.
(2) Within the next 125 flight hours after the effective date of this AD, unless previously accomplished within the last 875 flight hours, perform an operational check of the turbomachinery MCD airframe circuitry and indicating system in accordance with the applicable aircraft maintenance manual.
NOTE: Further information on the turbomachinery MCD airframe circuitry and indicating system specified in paragraph (c)(2) of this AD can be found in Fokker 50 Maintenance Manual, Chapter 77-33-00, for the PW125B, and BAe ATP Aircraft Maintenance Manual, Chapter 79-33-00, for the PW126A.
(3) Thereafter, at intervals not to exceed 1,000 flight hours since last inspection, perform the turbomachinery MCD operational check specified in paragraph (c)(1) of this AD.
(4) Thereafter, at intervals not to exceed 1,000 flight hours since last inspection, perform the operational check of the turbomachinery MCD airframe circuitry and indicating system in paragraph (c)(2) of this AD.
(d) The initial inspections of paragraphs (a)(1), (a)(2), and (b)(1) of this AD need not be accomplished for those PW123 and PW124B engines previously inspected in accordance with AD 90-24-05.
(e) Forengines that have not been modified in accordance with any revision level of PWC SB 21018, prior to the effective date of this AD, incorporate a new low pressure rotor balancing assembly in accordance with PWC SB 21018, Revision 2, dated November 25, 1991, at the next engine shop visit or by June 30, 1994, whichever occurs first. The incorporation of a new low pressure rotor balancing assembly in accordance with this paragraph constitutes a terminating action for paragraphs (a), (b), or (c), as applicable, of this AD.
(f) For the purpose of this AD, an engine shop visit is defined as the induction of an engine into a maintenance facility for the conduct of any type of maintenance.
(g) An alternative method of compliance or adjustment of the compliance time, which provides an acceptable level of safety, may be used when approved by the Manager, Engine Certification Office, ANE-140, Engine and Propeller Directorate, Aircraft Certification Service, FAA, New England Region, 12 New England Executive Park, Burlington, Massachusetts. The request shall be forwarded through an FAA Principal Maintenance Inspector, who may concur or comment and then send it to the Manager, Engine Certification Office.
(h) Special flight permits may be issued in accordance with FAR 21.197 and 21.199 to operate the airplane to a location where the requirements of this AD can be accomplished.
(i) The inspections and modifications shall be done in accordance with the following Pratt & Whitney Canada service documents:

Document Number
Page Number
Issue/Rev
Date
PWC SB 21018R2
1-36
Revision 2
11/25/91
Total: 36 pages

PWC SB 20938R2
1-8
Revision 2
11/18/91
Total: 8 pages

This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR Part 51. Copies may be obtained from Pratt & Whitney Canada, Technical Publications Department, 1000 Marie Victorin, Longueuil, Quebec J4G 1A1. Copiesmay be inspected at the FAA, New England Region, Office of the Assistant Chief Counsel, 12 New England Executive Park, Room 311, Burlington, Massachusetts, or at the Office of the Federal Register, 1100 L Street NW., Room 8401, Washington, D.C.
(j) This amendment becomes effective on May 26, 1992.