Witness Observations
Multiple witnesses reported seeing the airplane flying slowly at a low altitude while approaching the airport. The left engine was operating at a low rpm and produced abnormal noises described as "sputtering," "knocking," or a "banging" sound. Black smoke was trailing from the left engine. One witness stated that as the airplane passed overhead, the tail moved horizontally to the right and the airplane banked slightly to the left. Shortly thereafter, the airplane collided with trees and impacted a field located approximately half a mile north of the airport.
Engine and Propeller Examination
Post-accident disassembly of the right engine revealed no anomalies. The right propeller blades showed signatures consistent with power and rotation at the time of impact. The left propeller was found in the feathered position. Examination of the left engine disclosed that the spark plugs were black and heavily carbonized, indicating a rich fuel‑air mixture. The exhaust tubing also exhibited dark sooting. The rubber boot connecting the intercooler to the fuel injector servo was found dislodged and partially sucked inward toward the servo. The clamp used to secure the hose was loose but remained around the servo; the safety wire on the clamp was in place, and the clamp was not impact‑damaged or bent. The condition of the boot and clamp was consistent with improper installation.
Maintenance History
The left engine had accumulated approximately 1,050 hours since its last overhaul. The most recent 100‑hour inspection was performed three months before the accident, and the airplane had flown only 0.8 hour since that inspection. Investigators could not determine when the improper installation of the rubber boot occurred.
Performance Considerations
Although the left engine had failed, the pilot should have been able to fly the airplane and maintain altitude on the operable right engine, particularly since he had appropriately feathered the left engine.
Probable Cause
The pilot's failure to maintain sufficient clearance from trees during the single‑engine and landing approach. Contributing to the accident was the loss of power in the left engine due to an improperly installed rubber boot that became dislodged and was then partially sucked into the fuel injector servo, which caused an excessively rich fuel‑air mixture that would not support combustion.