Wheel & Exhaust Pipe Assy
Effective Date - 10/08/1979
Recurring - No
Supersedes - N/A
Superseded by - N/A
AIRESEARCH MANUFACTURING COMPANY OF ARIZONA
Applies to the following
groups of Model GTCP85 series Auxiliary Power Units (APUs) which have
cast turbine wheel Part Number 968095-1, -3, -5 or 3604604-1 installed:
Note: These APUs are installed in but not limited to Boeing 727-100/-200,
Lockheed L-100, Boeing 707 (conversion), Lockheed 382-Series, Douglas
DC-9, Avions Marcel Dassault - Breguet Aviation Mercure and British Aerospace
Corporation BAC 1-11, Trident 3B, Trident 1, and Trident 2E aircraft.
Group A: GTCP85-98CK, GTCP85-98CK(A), or GTCP85-98CK(B) with exhaust pipe
assembly Part Number 379529 or 976987-1.
Note: Part Number 976987-1 may be either a new production part or part
reworked from Part Number 379529 per AiResearch Service Bulletin 49-1790,
Revision 1, dated March 21, 1971, or original issue of this service bulletin.
Group B: GTCP85-98DCK, GTCP85-115CK, GTCP85-115H, GTCP84-139H, or GTCP85-163CK
with exhaust pipe assembly Part Number 379529 or 976987-1 reworked from
Part Number 379529 per Airesearch Service Bulletin 49-1790, Revision 1,
dated March 21, 1971, or original issue of this service bulletin.
Group C: GTCP85-185L with exhaust pipe assembly Part Number 899607-1.
Note: Operators of
airplanes incorporating the APUs affected by this airworthiness directive
are advised to examine the applicable sections of AiResearch Alert Service
Bulletin GTCP85-49-A5078, Revision 1, dated March 29, 1979, and AiResearch
Service Bulletin GTCP85-49-3688, Revision 5, dated February 9, 1979, to
identify production configuration of these units as well as the methods
of reworking the exhaust pipe assemblies to the approved replacement configuration.
as indicated. To prevent the release of high energy turbine wheel blade
fragments, accomplish the following, unless already accomplished:
(a) For APUs with turbine wheels Part Number 968095-1, -3, -5, or 3604604-1
installed, remove the exhaust pipe assemblies listed for Group A, B, and
C above and install a strengthened exhaust pipe assembly as defined below
at next APU overhaul, or within the next 3,000 operating cycles after
the effective date of this AD, whichever occurs first, or in any case,
not later than three years from the effective date of this AD.
(1) APUs in Group A are to have a Part Number 3607748-1, 966580-1, or
966580-3 exhaust pipe assembly installed.
(2) APUs in Group B are to have an exhaust pipe assembly Part Number 3607748-1,
966580-3, or an exhaust pipe assembly originally manufactured as Part
Number 976987-1 installed.
(3) APUs in Group C are to have a Part Number 3607748-1 exhaust pipe assembly
installed. Note: For the purposes of this AD, one cycle equals one start/shutdown
of the APU. If the operator does not have a record of operating cycles
on individual turbine wheels, he may assume two starts have occurred for
each recorded APU operating hour of service, or any other cycle per hour
ratio approved by the operator's assigned FAA maintenance inspector, provided
the request contains substantiating data to justify the alternative ratio.
Operators who have not kept a record of APU operating hours of service
shall estimate hours of APU operation by equating APU operation to airplane
hours time in service using a ratio approved by the operator's assigned
FAA maintenance inspector and justified by substantiating data.
(b) Special flight
permits may be issued in accordance with FAR 21.197 and 21.199 to operate
airplanes to a base for the accomplishment of modifications required by
(c) Alternative inspections,
modifications or other actions which provide an equivalent level of safety
may be used when approved by the Chief, Aircraft Engineering Division,
FAA Western Region. This amendment becomes effective October 8, 1979.