Accident Details
On May 28, 2014, about 1500 mountain daylight time, a Piper PA-25-235 airplane, N8808L, was substantially damaged during a forced landing near Boulder, Colorado. The commercial pilot sustained minor injuries. The airplane was registered to and operated by the Soaring Society of Boulder under 14 Code of Federal Regulations Part 91 without a flight plan. Day visual meteorological conditions prevailed for the local glider aero-tow flight that departed Boulder Municipal Airport (BDU) about 1430.
Sequence of Events
The pilot reported that the purpose of the accident flight was to aero-tow a glider to 10,200 feet mean sea level (msl) before returning to the departure airport. The aero-tow and glider release were uneventful. However, as the airplane was returning to BDU, the engine began to run intermittently while crossing over the foothills southwest of the airport. The engine eventually lost total power around 10,000 feet msl. The pilot did not attempt to restart the engine. Initially, he believed the airplane had sufficient altitude to glide to the airport, but it descended to an altitude requiring an off-airport landing. He decided to land on a nearby soccer field, but upon approach, he noticed power lines alongside the road bordering the field. The landing gear collided with a chain-link fence as he maneuvered the airplane below the power lines. After the gear became entangled, the airplane struck the road and came to rest in a drainage ditch. The right wing sustained substantial damage.
Fuel Management
The airplane's single fuel tank held 38 gallons, with 2 gallons considered unusable. The pilot reported that before his first flight of the day, the fuel level was about 1 inch from the top of the filler neck, and the fuel quantity sight gauge indicated near capacity. The operator stated that a 1-inch void equated to about 3.5 gallons of unused capacity, making the total usable fuel about 32.5 gallons before the first flight. The recording tachometer showed 3607.7 hours before the first flight and 3609.9 hours after the accident, indicating 2.2 tachometer hours had accumulated since the last refueling. The calculated average fuel consumption rate was about 14.8 gallons per tachometer hour since last refueling.
The operator's historical data from January–March 2014 showed an average consumption of about 10.2 gallons per tachometer hour. The previous pilot had flown 13 aero-tows with an average of 10.3 gallons per hour and confirmed he refueled after his final flight, leaving a 1-inch void. The accident pilot reported that the airplane had accumulated 1.9 tachometer hours during his first four aero-tow flights, and the fuel quantity sight gauge indicated slightly more than 10 gallons before the accident flight. Investigation determined the average fuel consumption for those four flights was at least 11.3 gallons per hour. The accident flight departed at 3609.6 tachometer hours and ended at 3609.9 hours, giving a duration of at least 0.3 tachometer hours before engine power loss.
Investigation
An on-site examination by a Federal Aviation Administration Inspector from the Denver Flight Standards District Office found that the airplane's single fuel tank was undamaged and void of any usable fuel. At 1456, the BDU weather observing system reported calm wind, 10 miles visibility, clear skies, temperature 30°C, dew point 5°C, and an altimeter setting of 30.10 inches of mercury.