Aircraft: Piper Twin Comanche. Injuries: 2 Fatal. Location: Canton, Mo. Aircraft damage: Destroyed.
What reportedly happened: The 74-year-old pilot’s logbook was destroyed in a hangar fire in 2011, but remaining records indicated that he had about 6,459 total flight hours and 809 multi-engine hours.
It could not be determined how many hours he had in a Twin Comanche. He also held an airframe and powerplant (A&P) mechanic’s rating and had inspection authorization (IA).
The airplane was purchased by the pilot on Oct. 15, 2011. The pilot performed the last annual maintenance inspection of the airplane and subsequent aircraft maintenance.
A witness, who was a private pilot, saw the twin-engine airplane flying overhead at an altitude of about 2,000 feet AGL. The airplane was in level flight, but the left propeller was not turning. The airplane crashed approximately 6.5 miles away from the witness.
Evidence indicated that the airplane struck a tree in a near wings-level attitude. Investigators noted that there were larger fields and flatter terrain with fewer obstacles northwest of the apparent route of flight.
The post-crash investigation also determined that the airplane was near or exceeded its maximum takeoff weight upon departure on the ill-fated flight. According to the airplane’s climb chart, it was unable to maintain altitude when the left engine lost power due to its excessive weight and single-engine performance, the existing high-density altitude of 2,963 feet and, possibly, the pilot’s execution of single-engine flight procedures, which left the pilot fewer options to reach a more suitable landing location.
The post-crash teardown of the engine indicated that the left engine experienced a total loss of power. The spark plugs in the Nos. 1, 2, and 4 cylinders, which had fuel primer lines attached, exhibited carbon-fouling, indicating that a rich-fuel mixture existed at the time of the accident and that the pilot most likely unsuccessfully attempted to regain the left engine’s power by using the fuel primer to prime the cylinders.
The left wing gascolator bowl was removed and a blue silicon gel-type sealant was found covering about two-thirds of the area of the bowl’s circumference and the area where a gasket is typically placed, however, no gasket was found in the gascolator. The blue silicon gel was consistent with Permatex Blue Silicon Gasket Maker, which has the following note in its directions: “Not recommended for use on head gaskets or parts in contact with gasoline.” If the gascolator seal is breached, air can enter the fuel system and possibly unport the carburetor, which would cause an uncommanded engine shutdown due to fuel starvation.
As the pilot was also an A&P/IA, investigators determined that he had likely performed the last annual maintenance inspection of the airplane and subsequent aircraft maintenance and improperly used the blue silicon sealant during maintenance operations.
Probable cause: The pilot’s improper decision to attempt to execute a forced landing to an open field with obstacles. Contributing to the accident was the left engine’s total loss of power due to fuel starvation as a result of the introduction of air into the fuel system through a gascolator seal breach and the pilot’s use of an improper substance on the left wing gascolator bowl during maintenance operations, which led to the gascolator seal breach.
NTSB Identification: CEN12FA586
This August 2012 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.