Service Bulletin No. 399 A

July 9, 2010

MODELS AFFECTED

All Lycoming series engines.

TIME OF COMPLIANCE

Prior to flight and/or during engine operation.

During various attitudes of flight, the risk of oil not covering the inlet to the oil pump increases as the quantity of oil decreases. Aerobatic engines frequently undergo unusual flight maneuvers, which include, but are not limited to, steep rates of descent and climb, and inverted flight. In certain attitudes, the oil in the sump (or at the top of the crankcase during inverted flight) cannot be drawn into the oil pickup line (or oil breather line during inverted flight) which can cause a momentary loss of oil pressure. If there is insufficient oil during flight, oil starvation can occur. Yet, not all low oil pressure incidents result in oil starvation.