Accident Overview
The pilot of a twin-engine airplane contacted Denver Air Route Traffic Control Center (ZDV) reporting a left engine oil leak and requesting landing at the nearest airport. ZDV informed the pilot that Akron (AKO) was the closest airport and cleared the aircraft to land there. After reporting the airport in sight, ZDV terminated radar service, instructed the pilot to switch to the advisory frequency, and reminded him to close his flight plan.
Approximately 17 minutes later, ZDV contacted Denver Flight Service Station (FSS) to inquire whether the aircraft had landed. Having received no communication from the pilot, Flight Service initiated a search. About 13 minutes later, the local sheriff located the aircraft off the airport.
Witness Accounts
Witnesses on the ground reported seeing the airplane flying westbound. They observed the airplane suddenly pitch nose down, "spiral two times, and crash." The airplane exploded on impact and was consumed by fire.
Examination Findings
An examination of the left engine revealed that the number 2 and 3 connecting rods were fractured at the journals. The number 2 and 3 pistons were heavily spalded. The engine case halves were fretted at the seam and through bolts. All six cylinders showed fretting between the bases and the case at the connecting bolts. The outside of the engine case exhibited heat and oil discoloration.
The right engine showed similar fretting at the case halves and cylinder bases, along with evidence of oil seepage around the seals. It also displayed heat and oil discoloration.
Propeller examination indicated that both propellers were at or near low pitch at the time of impact. The right propeller showed evidence of being operated under power, while the left propeller was operating under conditions of low or no power. According to the propeller manufacturer, during a sudden engine seizure, the propeller rpm is below the propeller lock latch rpm, preventing feathering.
Maintenance Records
Repair station records documented several instances of left engine oil leaks. One record noted a 3/4 inch crack found at a case half bolt beneath the induction manifold, which was repaired by retorquing the case halves and sealing the seam with an unapproved resin. Another record indicated that the station washed the engine and cowling as the repair action for an additional oil leak.
Probable Cause
The official probable cause identified the fractured connecting rods and the pilot not maintaining aircraft control following the engine failure. Contributing factors included low altitude, failure to maintain minimum controllable airspeed, inability to feather the propeller, oil exhaustion, seized pistons, and improper maintenance by the repair station.