The bulletin
Text extracted from the PDF.
SPECIAL
AIRWORTHINESS
INFORMATION
BULLETIN
AIRCRAFT CERTIFICATION SERVICE 800 INDEPENDENCE AVENUE, S.W.
WASHINGTON, DC 20591
U.S. Department of Transportation Federal Aviation Administration
No. ANE-95-01 June 19, 1995
Published by: FAA, AFS-613, P.O. Box 26460, Oklahoma City, OK 73125 This is issued for informational purposes only and any recommendation for corrective action is not mandatory.
INTRODUCTION
The purpose of this Special Airworthiness Information Bulletin is to advise International Civil Aviation Authorities (ICAAs) and FAA Flight Standards District Offices (FSDOs ) of the importance of incorporating Alert Service Bulletin (ASB) number 6178 on Pratt & Whitney (PW) JT8D engines. This bulletin recommends incorporation of the cutback 3rd turbine blade, ASB 6178, on JT8D-15A/-17A/- 17AR engine models that have not yet incorporated the cutback 3rd turbine blades. However, this bulletin is for information purposes only and the recommendations contained herein are not mandatory.
BACKGROUND
The FAA issued Airworthiness Directives (AD) 94-20-08 and 94-20-09 in October 1994 to require installation of low pressure turbine (LPT) containm ent hardware. AD 94-20-09 was applicable to "A" model engines (JT8D-15A/-17A/-17AR) and AD 94-20-08 w as applicable to all other basic JT8D engine (non-A) models. The LPT containment hardware c onsisted of a strengthene d fan duct segment and thicker honeycomb air seal to provide improved sh ielding from engine debris (ASB 6110). The containment hardware also included a bushing on th e bearing scavenge pump bracket (ASB 6131) and a cutback of the flow guide vanes (ASB 5748, A models only) to ensure rotor meshing in the event of a shaft fracture. An experimental engine test by PW on an "A " model engine in which a shaft failure was induced revealed that the eff ectiveness of the rotor meshing w as limited by the presence of excess material on the rear face of the 3rd turbine blade plat form. This blade is unique to the "A" model engines and the containment capability of the non-A engines is adequate once AD 94-20-08 is complied with.
Meshing did occur during the engine test, but th e rotor exceeded the maxi mum speed at which the released turbine blades would be contained. The engine test was intended to simulate worst case conditions, and therefore, compliance with AD 94-20- 09 will provide containment protection under most circumstances. However, compliance with AS B 6178 concurrent with AD 94-20-09 compliance will ensure the maximum level of containment protection is provided.
RECOMMENDATIONS
ICAAs and FAA FSDOs should recommend that operators of JT8D-15A/-17A/-17AR engine models incorporate PW ASB 6178 when incorporating the other containment hardware specified in AD 94-20-09.
FOR FURTHER INFORMATION CONTACT:
Federal Aviation Administration; ATTN: Mr. Mark A. Rumizen, ANE-142; 12 New England Executive Park; Burlington, MA 01803; USA; Telephone: (617) 238-7137; Fax: (617) 238-7199