What happened
The pilot was operating the unspecified aircraft under Visual Flight Rules (VFR) at 1,500 feet MSL while returning to his home airport. During a slow climb toward 3,000 feet, the pilot observed a drop in propeller RPM on the right engine. Simultaneously, a passenger reported seeing oil leaking from the engine.
In response to the failure, the pilot shut down and feathered the right engine. However, the aircraft was unable to maintain sufficient altitude or airspeed on the remaining left engine. The pilot subsequently decided to perform an off-airport landing on a closed highway. During the approach, the propeller of the left engine struck a powerline. The pilot was unable to regain control of the aircraft before it impacted the ground.
The investigation
An examination of the engines during teardown revealed no mechanical discrepancies. However, a post-impact fire caused extensive damage to the exterior of the engines and the oil lines, making it impossible to determine the original source of the oil leak.