"Several Conditions" Could Result In Loss Of Power

The FAA has revised an SAIB (Special Airworthiness Information Bulletin) concerning a condition on certain 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.

The FAA says that 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. At this time, the airworthiness concern is not an unsafe condition that would warrant the issuance of an AD.

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 allows 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.

The FAA indicates that 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.

The only change in the previous SAIB is that the FAA now recommends that pilots and owners ensure that the facility overhauling magnetos on these engines has inspected, or will inspect, the magneto housing for cracks by using a form of nondestructive  test (NDT). There are no NDT instructions in the current TCM Magneto Overhaul Manual. A documented procedure using a Level III fluorescent penetrant material, as specified in either current version of SAE International Standards Document SAE 2647 or ASTM International Standards Document ASTM 1417, is acceptable. A procedure recommended by TCM is also acceptable. A Qualified Inspector, as specified in FAA Advisory Circular 43-13 or MIL Standard 410, is to perform the fluorescent-penetrant inspection. A qualified FAA Airframe and Powerplant Mechanic may also perform the fluorescent-penetrant inspection.

FMI: www.faa.gov