Aircraft
Certification Service Washington, DC U.S. Department of Transportation Federal Aviation Administration
NE-08-26
June 2, 2008
This is information only. Recommendations
aren’t mandatory.
Introduction
This Special Airworthiness Information Bulletin (SAIB) alerts you,
owners, operators, and certificated repair facilities of Lycoming four,
six, and eight cylinder reciprocating engines with a Teledyne
Continental Motors (TCM) (formerly Bendix) Series D2000 and D3000 Dual
Magneto (2 magnetos with a single drive). Several conditions identified
could result in separation of the magneto from the engine, which will
result in the loss of power. These engines can be identified by the
letter “D” in the 4th or 5th character in the engine model’s suffix.
Most of the problems have occurred in Lycoming IO-360-A1B6D and
IO-360-A3B6D engines installed on Mooney M20J-201 and Cessna 177RG
aircraft, although the potential for magneto separation exists on any
engine with a TCM Dual Magneto installed.
Background
For various reasons, several incidents of TCM Dual Magnetos separating from Lycoming engines during flight have occurred.
One failure occurred on the first flight after installation of a newly
overhauled magneto. The failure occurred due to cracks in the magneto
housing mounting flange area that were present as a result of the
magneto’s prior operation. During the overhaul process, the overhaul
manual only required visual inspection of the magneto.
Another failure mode has been due to the use of the wrong gasket
between the magneto and the engine accessory housing. Lycoming Service
Instruction (SI) 1508B clearly shows that the gasket must be circular
and no part of the gasket can extend beyond the flange of the magneto
housing. To be more specific, using a gasket with extensions on the
outside diameter that allow the stud from the accessory housing to go
through the gasket, and position the gasket between the magneto clamp
and the accessory housing, is unacceptable. When a gasket is located
between the magneto clamp and accessory housing it will compress and in
time result in a loose magneto. A loose magneto will result in the
magneto clamp wearing into the magneto mounting flange. Ultimately, the
flange thickness will be reduced and the flange will fail.
Improper maintenance usually occurs when magneto maintenance is
performed in the field and the nuts holding the magneto clamps in
position are removed or loosened. When these nuts are reinstalled, new
lock washers must be used because they lose their locking ability with
repetitive usage. The ability to obtain the proper torque on the nuts
securing the magneto clamps or even make them adequately tight depends
on the accessibility of the nuts when the engine is installed in the
airplane. Magnetos are more accessible on some airplanes than on others
and obtaining the correct torque is easier. However, on some
installations, the working room is limited and the magneto clamping
nuts are inaccessible making proper torquing difficult. As stated
above, most of the problems have occurred on Lycoming IO-360-A1B6D and
IO-360-A3B6D engines installed in Mooney M20J-201 and Cessna 177RG
aircraft because of inaccessibility of the nuts securing the magneto
clamps.
Recommendations
1. Before installing a magneto, check the magneto housing mounting
flange for wear and cracks. A worn or cracked flange might subsequently
fail, resulting in the magneto separating from the engine. If the
flange is worn or cracked, replace the magneto.
2. Only install the correct gasket, part number (P/N) LW-12681, which
is a circular gasket, between the magneto housing mounting flange and
the engine accessory housing. Gasket, P/N LW-12681, does not extend
over the magneto mounting studs and it must not be installed between
the magneto clamps and the engine accessory housing. If a gasket is
installed between the magneto clamps and the engine accessory housing,
it is the wrong gasket and must be replaced.
3. Only use the new style magneto clamps, P/N 66M19285.
4. Each time a magneto clamp is removed, install a new lock washer, P/N STD-475, before reinstalling the nut, P/N STD-1410.
5. Torque the nuts that secure the magneto to the accessory housing
using the torque specified in Lycoming Service Instruction No. 1508B.
6. Repetitively inspect the magneto for looseness by attempting to move
it by hand, at each oil change or within every 50 operating hours
time-in-service. If the magneto is loose, visually check the magneto
mounting flange for wear and cracks. If no wear or cracks are present,
re-torque nuts, P/N STD-1410, as specified in Lycoming Service
Instruction No. 1508B. If the flange is worn or cracked, replace the
magneto.
7. Repetitively check the torque on the magneto clamp nuts, P/N
STD-1410, with a torque wrench at each annual or 100-hour inspection.
If is the nuts are loose, visually check the magneto mounting flange
for wear and cracks. If no wear or cracks are present, re-torque the
nuts, as specified in Lycoming Service Instruction No. 1508B. If the
flange is worn or cracked, replace the magneto.
8. Cracks in the magneto mounting flange may have been caused by prior
operation of the engine with loose magneto clamps. We strongly
recommend that you ensure that the facility overhauling your magneto,
has inspected, or will inspect, the magneto housing for cracks by using
a form of nondestructive test (NDT) such as fluorescent-penetrant
inspection (FPI), dye-penetrant inspection (DPI), or by a procedure
recommended by TCM. Since there are no NDT instructions in the current
TCM Magneto Overhaul Manual, we recommend the use of an FPI or DPI,
performed by a Level 1 Certified person or a person with an FAA
Airframe and Powerplant Mechanic Certificate as specified in FAA
Advisory Circular 43-13, Chapter 5.
9. Refer to Lycoming Service Instruction No. 1508B for additional information.
For Further Information Contact
Norm Perenson, Aerospace Engineer, New York Aircraft Certification
Office, FAA, 1600 Stewart Avenue, Suite 410, Westbury, NY 11590; phone:
(516) 228-7337; fax: (516) 794-5531; e-mail: norman.perenson@faa.gov.
For Related Service Information Contact
Lycoming Engines, 652 Oliver St, Williamsport, PA 17701; phone: (570)
323-6181; fax: (570) 327-7101; or go to their Web site at:
http://www.lycoming.textron.com/support/publications/serviceinstructions/pdfs/SI1508B.pdf.