Accident Overview
On July 13, 2015, about 1520 central daylight time, a Piper PA-30 airplane, registration N7768Y, was destroyed during an attempted forced landing to runway 14 at Clifton Municipal Airport (7F7), near Clifton, Texas. The pilot, who held an airline transport pilot certificate, received minor injuries. The airplane was registered to and operated by the pilot as a 14 Code of Federal Regulations Part 91 personal flight. Visual meteorological conditions prevailed for the flight, which was not on a flight plan. The flight was originating at the time of the accident and was destined for the San Antonio International Airport (SAT), San Antonio, Texas.
Pilot Report
The pilot reported that the accident flight was the first flight following an annual inspection of the airplane. He performed a pre-flight inspection that included checking fuel, oil, and the replacement and securing of access panels. Both engines started immediately and pre-takeoff checks were normal. On takeoff, all engine instrument readings were normal except the fuel flow for the right engine, which read 17 gallons per hour versus the expected 14 gallons per hour. After becoming airborne, the right engine fuel flow remained elevated and the engine RPM was at maximum. The right engine exhaust gas temperature (EGT) was about 100 degrees lower than that of the left engine. He noted that normally the EGT readings were very close. He retarded the propeller control lever with no change in RPM; cycling the prop lever had no effect, and he decided to return to 7F7. As he turned onto a downwind traffic pattern leg, the right engine suddenly stopped with no warning. The engine RPM reduced rapidly and the propeller would not windmill. He was unable to restart or feather the failed right engine. During the ensuing forced landing, about 20 ft above ground level, the airplane suddenly and violently rolled to the right. The airplane traveled across the taxiway parallel to the runway, onto the ramp, and came to rest behind a row of buildings on the southwest side of the runway. During the event, the airplane struck another airplane parked on the ramp area. The airplane immediately caught fire and the pilot exited unaided.
The pilot reported that his normal procedure was to take off with the fuel selectors positioned for the main fuel tanks. He did not recall attempting to switch fuel tanks during the restart attempts. He had reported having 58 gallons of fuel on-board prior to the accident flight and typically had 2 to 5 gallons in each auxiliary tank with the remainder in the main tanks, balanced left to right.
Witness Observations
A witness reported seeing the airplane in a wing-down, nose-down attitude heading toward the aircraft parking area. When the airplane came to rest, he retrieved a fire extinguisher and began putting out fires in and around the airplane. Another witness reported that once the fires were under control, he entered the cockpit to turn off the emergency locator transmitter and shut off the fuel selectors. Upon shutting off the fuel selectors, the witness noted that the right fuel selector was only one detent from the off position, indicating it was positioned for the auxiliary fuel tank.
Post-Accident Examination
Examination of the airplane after the accident revealed that neither propeller was in the feathered position. The left propeller dome pressure was about 50 psi, but no dome pressure was measurable on the right propeller. Both propeller air fill valves had caps. According to propeller manufacturer documentation, the dome charge should have been 50 psi. Examination of the right propeller revealed that the air fill valve seal was contaminated by a small piece of debris. Once removed, the propeller dome was charged with air and held pressure. The propeller start locks were engaged, which would prevent feathering. Propeller manufacturer documentation stated that a low air charge could result in little or no effect on propeller RPM control. The start lock should engage when engine RPM drops below 700 to 900 RPM. The manufacturer indicated that the propeller would still feather normally if the dome was not charged, provided sufficient RPM to prevent premature start lock engagement.
The left engine was examined after removal; it could be rotated by hand with compression and suction verified on all cylinders. Spark was observed on all magneto leads. A differential compression test showed readings above 65/80 on all cylinders except number 2 at 50/80. The number 2 cylinder was removed and examined with no defects noted. The differential compression test was performed on a cold engine not operated for several months. Magneto timing was within specifications. The fuel control unit was tested on a test flow bench and all measurements were within service limits.
The right engine could be rotated by hand with suction and compression verified. Spark was observed on all magneto leads. Differential compression readings exceeded 65/80 on all cylinders. Magneto timing was within specifications. The fuel control unit was tested and all measurements were within service limits.
The airplane's fuel system was examined; compressed air was used to blow through fuel lines with a catch bottle. Recovered fuel was pale blue, consistent with 100LL aviation gasoline, with no contaminants. Fuel selector valve operation was confirmed and no anomalies were noted. Fuel strainer bowls were removed and found free of debris.