History of Flight
On April 27, 2014, about 1700 eastern daylight time, an Alon A2, registration N6364V, experienced a total loss of engine power shortly after takeoff from Deck Airpark (NC11), Apex, North Carolina. The pilot made an off-airport forced landing into a forest. The private pilot sustained minor injuries; the passenger was not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the local flight. The airplane was registered to and operated by a private individual under 14 CFR Part 91 as a personal flight.
The pilot reported that the taxi and initial takeoff were normal. When the airplane was about 100 feet above the trees bordering the airport, the engine experienced a total loss of power. The pilot retarded the throttle and immediately reapplied full throttle; the engine restarted but immediately lost power again. He performed a forced landing into the trees about 500 feet past the departure end of the runway. The pilot reported having about 15 gallons of autogas in the fuel tanks prior to departure.
Personnel Information
According to pilot-provided information and Federal Aviation Administration (FAA) records, the pilot held a private pilot certificate with a rating for airplane single-engine land and a third-class medical certificate issued on August 20, 2013. The pilot reported 1,471.6 total flight hours, with 38.3 hours in the accident airplane make and model.
Aircraft Information
The accident airplane, an Alon A2 (serial number A-40), was manufactured in 1965 and registered with the FAA on a standard airworthiness certificate for normal operations. The airplane had a total time of 1,872.36 hours as of the last annual inspection on January 4, 2014. It was powered by a Continental C90 series engine, which had accumulated 1,661 total hours and 287 hours since last major overhaul as of the last annual inspection.
Meteorological Information
The 1651 recorded weather observation at Raleigh-Durham International Airport (RDU), about 10 miles northeast of the accident location, included wind from 210 degrees at 6 knots, 10 miles visibility, scattered clouds at 25,000 feet above ground level, temperature 28.3°C, dew point 8.9°C, and altimeter setting 29.92 inches of mercury.
Wreckage and Impact Information
Initial examination by an FAA inspector revealed that the airplane impacted several trees and came to rest inverted between two trees, resulting in substantial damage to the wings and fuselage. Local authorities reported a strong fuel smell at the accident scene; however, the fuel tank selected at takeoff was not noted or provided to the NTSB.
Additional Information
A subsequent engine examination at a storage facility under NTSB oversight revealed minimal external damage. The throttle, mixture, and carburetor heat controls remained attached and operated without anomalies. The engine remained attached to the airframe and was fitted with a 5-gallon fuel container between the wing root and carburetor to facilitate an engine run. The wings were removed at the wing root for transport; continuity was not confirmed from the fuel tank to the separation point. The engine started and operated through various power settings with no abnormalities noted. No anomalies were noted from the 5-gallon fuel container through the fuel system.
FAA guidance in an NTSB accident report (ERA12LA131) noted that testing revealed vapor pressure of autogas can vary widely due to seasonal formulation changes and local requirements. High vapor pressure can promote vapor lock in aircraft fuel systems, causing engine power reduction or complete failure. Additionally, testing by the FAA William J. Hughes Technical Center concluded that autogas with high vapor pressure can accelerate carburetor ice formation.
The Pilot's Handbook of Aeronautical Knowledge defines vapor lock as a problem that occurs when liquid fuel changes state to gas in the fuel delivery system, disrupting fuel pump operation and causing loss of feed pressure, resulting in transient power loss or complete stalling. Restarting may be difficult.
Document DOT/FAA/CT-87/05 states that worst-case conditions for vapor lock testing include takeoff fuel flow, initial fuel temperature between 38 and 43°C, ambient air temperature 29°C or higher, engine at operating temperatures after prolonged idling or hot soak, and ASTM class E (winter grade) fuel for autogas.
An FAA chart titled "Conditions Favoring Carb Ice Formation" indicated that with the ambient temperature and dew point, "Icing at glide and cruise power" was probable.