AD 54-02-01

54-02-01 LYCOMING: Applies to All Model O-290-D2 Engines. Compliance required by February 1, 1954, and at each subsequent 100-hour inspection. In order to preclude the possibility of serious engine damage from incipient detonation under certain atmospheric and altitude conditions, the magneto timing of all Lycoming O-290-D2 engines must be set at 18 degrees BTC. To insure that the magneto timing does not change substantially from this setting, it should be checked and reset, if necessary, at each subsequent 100-hour inspection. (Lycoming Service Bulletin No. 169 covers this same subject, but recommends that the timing be checked every 50 hours.)