AD 84-17-51

84-17-51 R1 ALLISON GAS TURBINE DIVISION GENERAL MOTORS CORP. (ALLISON, formerly DETROIT DIESEL ALLISON): Amendment 39-4963. Applies to Allison Model 250-C30 and 250-C30S engines having 100 hours or less time in service since gas producer turbine rotor assembly repair or disassembly and installed in Sikorsky S76A helicopters certified in all categories. Compliance is required as indicated unless already accomplished. To prevent abnormal rub of the second stage turbine nozzle interstage seal which could result in an overspeed burst of the first stage turbine wheel, accomplish the following: (a) Within the next 50 hours time in service after August 31, 1984, inspect the second stage turbine nozzle interstage seal for rub in accordance with Allison Commercial Engine Alert Bulletin CEB-A-72-3127 dated September 14, 1984, or Revision 1 dated November 15, 1984, or FAA-approved equivalent. NOTE: Prior to September 14, 1984, evidence of rub evaluated by the engine manufacturer anddetermined suitable for continued use in service is equivalent to compliance with the above bulletins. (b) Components exhibiting signs of abnormal rub as defined in paragraph (a) above must be replaced with serviceable components prior to return to service. The repair or replacement as necessary, with additional assembly, alignment, and test procedures are to be performed in accordance with the following: (1) Repair/Replacement, Additional Assembly, and Alignment Procedures. (i) Allison Commercial Engine Alert Bulletin CEB-A-72-3127 dated September 14, 1984, or Revision 1 dated November 15, 1984, or FAA approved equivalent. (ii) Prior to September 14, 1984, compliance with Allison message THO-1977W-RMG-84 dated August 18, 1984, is acceptable. (2) Second Stage Nozzle Interstage Seal (29-34 Labyrinth Seal) Clearance. (i) Allison Commercial Engine Alert Bulletin CEB-A-72-3131 dated November 15, 1984, or Allison message THO-2111W-RMG-84 dated September 21, 1984,or FAA approved equivalent. (ii) Prior to November 15, 1984, compliance with Allison Commercial Engine Alert Bulletin CEB-A-72-3127 dated September 14, 1984, or Allison message THO-1977W-RMG-84 dated August 18, 1984, is acceptable. (3) Test Stand Requirements for Model 250-C30 and -C30S Engines that Have Undergone The Gas Producer Turbine Special Inspection on the Second Stage Turbine Nozzle. (i) Allison Distributor Information Letter 250 DIL 223 dated October 1, 1984, or FAA approved equivalent. (ii) Prior to October 31, 1984, compliance with Allison message THO-1979W-RMG-84 dated August 22, 1984, as revised by THO-2032W-RTM-84 (Revision No. 1) dated September 11, 1984, is acceptable. (c) Special flight permits may be issued in accordance with FAR 21.197 and 21.199 to operate helicopters to a base for accomplishment of this AD. (d) Upon request, an equivalent means of compliance with the requirements of this AD may be approved by the Manager, Chicago AircraftCertification Office, FAA, 2300 East Devon Avenue, Des Plaines, Illinois 60018. NOTE: Gas producer turbine rotor assembly repair or disassembly includes replacement of any gas producer turbine rotor assembly from the total turbine assembly, or maintenance/repair performed on the gas producer turbine rotor assembly associated bearings/seals/parts starting with the No. 7 bearing and ending with the No. 8 bearing oil sump cover. Compliance with AD 83-22-05 (Allison CEB A-72-3108) does not constitute gas producer turbine rotor assembly repair or disassembly provided no corrective action as outlined above is accomplished as a result of the inspection/cleaning. The manufacturer's specifications and procedures identified and described in this directive are incorporated herein and made a part hereof pursuant to 5 U.S.C. 552(a)(1). All persons affected by this directive who have not already received these documents from the manufacturer may obtain copies upon request to Allison Gas Turbine Division, General Motors Corporation, P.O. Box 420, Indianapolis, Indiana 46206-0420. These documents also may be examined at the Office of the Regional Counsel, FAA, ATTN: Rules Docket No. 84-ANE-13, 12 New England Executive Park, Burlington, Massachusetts 01803, weekdays, except federal holidays, between 8:00 a.m. and 4:30 p.m. This amendment becomes effective December 26, 1984, to all persons except those persons to whom it was made immediately effective by telegraphic AD T84-17-51, issued August 31, 1984.