On September 23, 2012, about 0935 Pacific daylight time, a Navion-A airplane, N4418K, sustained substantial damage following a forced landing due to a loss of engine power shortly after takeoff from the Lompoc Airport (LPC), Lompoc, California. The certified commercial pilot, the sole occupant, was not injured. Visual meteorological conditions prevailed at the time of the accident, and a flight plan was not filed. The personal cross-country flight was being operated in accordance with 14 Code of Federal Regulations Part 91. The reported destination was the Lodi Airport (1O3), Lodi, California. In a statement submitted to the National Transportation Safety Board investigator-in-charge, the pilot reported that after taking off and while entering a left downwind leg at 1,200 feet, the engine began to lose power; after turning the boost pump on there was a total loss of power. The pilot stated that he then turned back toward the departure runway, turned the hydraulic power on and lowered the landing gear; the landing gear was retracted when the pilot realized he was too far from the runway to make a safe landing. The pilot opined that he maneuvered over power lines, turned about 30 degrees to the right and flew through the lowest gap in the approaching trees. The airplane landed in a soft dirt field and slid about 80 feet before coming to rest in an upright position. The airplane sustained substantial damage to the aft fuselage. A Federal Aviation Administration (FAA) aviation safety inspector reported that during his initial inspection of the engine the fuel pressure measured at the carburetor was 5 pounds per square inch (psi). The inspector further reported that after testing the fuel pressure several times the pressure increased to 10 psi, and that during a bench test of the relief valve, pressure at the relief valve was confirmed to be 10.5 psi; the engine requires a minimum pressure of 9 to 15 psi under normal conditions. Under the supervision of a FAA aviation safety inspector, the carburetor and boost pump were examined at the facilities of KPS Airmotive, Santa Clarita, California. The results of the examination revealed no anomalies with either component that would have precluded normal operation. (Refer to the KPS Airmotive report, which is appended to this report.) Maintenance records revealed that both magnetos and the airplane's boost pump were overhauled on June 21, 2012. At 0935, the LPC weather reporting facility, located about 3 nautical miles north of the accident site, reported wind 260 degree at 3 knots, visibility 10 miles, scattered clouds at 400 feet, temperature 15 degrees Celsius (C), dew point 11 degrees C, and an altimeter setting of 29.99 inches of mercury. The reason for the reported total loss of engine power was undetermined.