The Exception
Early model Lycoming engines,
early 1960's, were manufactured with a two piece oil pump body using a
combination of a steel impeller running against an aluminum impeller. The
aluminum impeller rotated on a fixed steel shaft that was pressed into the oil pump
housing and secured with a cotter pin. In 1965, a one
piece housing was introduced also using the fixed steel shaft and secured with
a cotter pin. These oil pump impellers are not affected
by this AD. (Fig. 1)
Lycoming
Service Instruction 1164A, references that the two piece oil pump housings are
no longer available as replacement parts. If the housing or impellers need
replacement, the new style housing and impellers will need to be installed.
AD 81-18-04r2
In the early 1970's, Lycoming changed from a steel and aluminum oil pump
impeller configuration to a steel impeller
and a sintered iron impeller. This combination had a high failure rate and
resulted in the issuance of AD 81-18-04.
This
AD called for the replacement of both the steel and sintered iron impellers and the installation of a steel driving
impeller, part # 60746 and an aluminum impeller and shaft part # LW-13775
(Fig. 2)
Oil Pump Failures continue.
Failures
continued to plague the new combination of oil pump impellers, and in January,
1994, the FAA proposed an amendment to AD 81-18-04r2 to include the replacement
of the aluminum impellers with a hardened steel impeller and shaft.
On
July 15,1996, The FAA superseded AD 81-18-04r2 and
issued AD 96-09-10.
The AD
calls for the replacement of all aluminum impellers, part # LW-13775. The
impellers must be replaced during one of the following. The
next over-haul, oil pump change, at the published TBO, or a calendar
date of five years from the date of the AD. That date of July 15, 1996
will have a deadline of July 15, 2001.
Which Impeller do you
have?
Engines originally manufactured
before 1970 did not incorporate sintered iron impellers. For these engines,
reference should be made to engine maintenance / overhaul logbook records,
Lycoming build records and pertinent service bulletins. Service bulletin nos.
381C & 385C describe a method of removing the right magneto to observe
whether or not a cotter pin is visible on the oil pump
housing. If this cotter pin is visible, (Fig 1) your
oil pump impellers are NOT subject to this AD. If you oil pump does not have
the cotter pin visible, (fig 4) The AD does apply unless engine records
indicate that the impellers have been replaced. The new impellers became available in 1987. An overhaul before this date
would indicate the need for the AD compliance in the upcoming year. However, an
overhaul after this date does not mean the impellers were changed.
PN 05K19423-S
is the Lycoming kit number for
the new impellers. If you engine has been overhauled since 1987 and the above
part number is included in your engine overhaul records, then the AD has been
complied with. (See fig. 3)
Cost of AD
The FAA estimated that the time required to comply
with the AD was 4.5 hours labor and approximately $270.00 in parts in 1996. This
time estimate was based on an engine removed from the aircraft and did not
include engine removal and installation. Estimated time to replace the impellers
on a Mooney, which will require engine removal, are 15 to 20 hours and
parts in the $300.00 to 500.00 range. The FAA estimated that 29,000 engines in
the U.S. alone would be affected with a cost impact of $15,660,000.00.
AD Confusion
The previous AD 81-18-04r2 was unclear as
to whether the AD applied to all aluminum impellers.
According to the former and current AD language, I read the AD to apply to all
aluminum impellers including the ones found in the two piece housing. After
much debate with fellow A&P’s and research, I
finally located the “PREAMBLE” to AD 96-09-10. This document clearly states
that the AD does not apply to the aluminum impellers in the two piece housing.
The AD applies only to part # LW13775. I
will forward this document to Bob and Leila at MAPA
if you need a copy for your mechanic. Additional reference material
are Lycoming SB numbers 381-C, 385-C, 454-B, 455-D, 456-F and 524. These
documents are available from Lycoming or your local Service center. Be sure and check for this AD compliance during your pre-buy inspection. This is one of
those “sleeper” AD’s that could become very
expensive.
Don
Maxwell
