On May 1, 2019, about 1001 Pacific daylight time, a special light sport Storch Aircraft LLC, N156LZ, was substantially damaged when it was involved in an accident near Upland, California. The pilot was seriously injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.
According to the pilot, after takeoff, as the airplane climbed through about 300 ft, the engine lost oil pressure but continued to produce power. As the pilot maneuvered the airplane toward the departure airport, the engine suddenly stopped developing power. The airplane touched down in a field east of the airport and came to rest upright.
A review of photographs provided by the Federal Aviation Administration (FAA) revealed substantial damage to the forward cabin and engine truss.
An examination of the engine performed by the FAA revealed that the No. 3 cylinder valve cover was loose (see figure 1), with a gap about 1/4-inch between the cylinder and the cover; oil was found throughout the engine and the engine compartment. Oil was discovered outside the hangar where the pilot started the engine for the accident flight, and an oil trail led to the runup area he used, which also exhibited oil spray (see figure 2).
Figure 1. Close-up view of No. 3 cylinder valve cover
Figure 2. Oil residue discovered on taxiway in relation to pilot’s hangar and wreckage site
A review of the airplane’s maintenance records revealed that the engine was removed on May 24, 2018, and reinstalled on August 31, 2018, by the pilot. No other maintenance on the engine was recorded in the logbooks. The pilot reported that before the last flight, he removed the valve covers to inspect the crankcase throughbolts and “thought” he retorqued all four valve cover screws. He re-examined the valve covers after the accident and confirmed that the No. 3 cylinder valve cover was loose.
The Rotax Powertrain Maintenance Manual 72-00-00 pg. 93, instructs, “fit valve cover and tighten with allen screw M6x30 and washer to a tightening torque of 10 Nm (90 in. lbs).” The caution associated with the tightening of the allen screw at reinstallation stated:
IF THIS SCREW IS LOOSE OR IF THE VALVE COVER IS LEAKING, THE OIL RETURN TO THE OIL TANK BY “BLOW-BY GAS” WILL NOT WORK PROPERLY AT ALL OR ONLY INSUFFICIENTLY.
According to the engine manufacturer, the oil system relies on crankcase pressure to return oil back to the tank from the crankcase. The valve covers need to be sealed, as this crankcase pressure will escape from that location and oil will not return to the tank. If the No. 3 valve cover is loose during an engine start-up, the inadequate seal would result in a substantial oil leak, followed by an imminent engine failure due to oil starvation.