Incident Sequence
During a training flight, the pilot preflighted the airplane and added 1 1/2 quarts of oil before departure. After takeoff, at approximately 100 feet above ground level, oil began spreading backward onto the windscreen. The instructor took control of the aircraft and reduced power to prevent overheating. Both occupants perceived an uncommanded reduction in propeller RPM and determined that continued flight was not possible. The pilot reported that the engine "felt and sounded normal" when the airplane impacted trees.
Inspection Findings
Post-accident examination revealed that the engine oil filler cap was removed and hanging by a chain. Oil that had spread aft over the engine and cowling formed a fan-shaped pattern approximately 30 degrees wide, originating at the oil filler cap location. No pre-impact failures or malfunctions were found with either the engine or the airframe.
Reference to Pilot's Operating Handbook
The pilot's operating handbook states: "When oil pressure to the piston in the propeller hub is relieved, centrifugal force, assisted by an internal spring, twists the blades towards low pitch (high RPM)." This description was noted in the context of the perceived propeller RPM reduction.
Training Experience
The instructor had 4 hours of flight experience in the accident airplane's make and model. The pilot had 13 hours in the accident airplane's make and model.