NTSB Factual Report

HISTORY OF THE FLIGHT

On July 22, 2006, about 1830 Pacific daylight time, a Piper PA-28-161, N2115R, overran the runway surface following a forced landing at Nevada County Air Park, Grass Valley, California. The pilot owned and operated the airplane under the provisions of 14 CFR Part 91. The private pilot, the sole occupant, was not injured; the airplane was substantially damaged. Visual meteorological conditions prevailed, and no flight plan was filed for the local area personal flight. The flight was originating at the time of the accident.

In a written statement, the pilot stated that he arrived at the airport about 1800 to perform touch-and-go takeoffs and landings. The pilot intended to verify the performance of the airplane "lightly loaded." He planned to fly to Murray Field Airport, Eureka, California, or Arcata Airport, Arcata/Eureka, California, the following day. Following a preflight, which included sumping both fuel tanks and checking the oil, the pilot checked the automated weather observation system (AWOS). He recalled that the AWOS transmitted a density altitude of 6,150 feet, and the pilot indicated that he knew from past experience that this was well within the takeoff performance charts outlined in the pilot's operating handbook (POH) and that the runway length at Grass Valley was adequate based on the performance data. He started the engine on the right fuel tank and then switched to the left. The right fuel tank contained about 6 gallons and the left tank contained about 12 gallons. He turned off the fuel pump and taxied to the run-up area for runway 25.

During the run-up, the pilot noted a 90-revolutions per minute (rpm) drop during each magneto check while running the engine at 2,000 rpm. The fuel pressure was at the lower portion of the green arc when the electric fuel pump was not on. When the pump was turned on, the fuel pressure increased.

The pilot taxied onto the runway and applied full power. The acceleration was normal until approximately a few feet above the runway, when there was a power drop. The pilot closed the throttle and aborted the takeoff. As he taxied from the runway, the pilot noted that the fuel pressure gauge was indicating normal with the electric fuel pump on. During the deceleration, there was no change in engine sound and it ran smoothly.

After arriving to the run-up area for a second time, he performed a full power run-up. Full throttle application indicated 2,200 rpm. After going through the magneto checks and checking the fuel pressure, he attempted a second takeoff. The airplane rotated from the runway at 60 knots indicated airspeed (KIAS) and climbed to an altitude of about 60 feet. At this point, the engine lost power again and he was forced to land the airplane on the remaining runway. He closed the throttle, extended the flaps two or three notches, and touched down on the remaining runway. He applied the brakes but the airplane skidded off the end of runway 25 into rough terrain.

The pilot stated that he did not lean the mixture setting prior to either takeoff. In addition, the airplane was parked uncovered on the ramp.

In the owner safety recommendation section of the Pilot Operator Report, NTSB Form 6120.1/2, the pilot noted that a better understanding of vapor lock symptoms and go/no go indications when conditions warrant would have assisted him in the decision to attempt the flight.

This accident was upgraded from an incident on July 31, 2006, following an airplane examination by a Federal Aviation Administration (FAA) Sacramento Flight Standards District Office inspector. The inspector noted that the firewall was bent and the right wing leading edge sustained damage.

TESTS AND RESEARCH

An aviation maintenance technician (AMT) with an inspection authorization examined the Textron Lycoming O-320-D3G engine under the auspices of an FAA inspector. The spark plugs were removed and examined; the electrode wear was similar among the plugs and all were light gray in color. The lower spark plug for cylinder number 1 had oil on it. The spark plugs were reinstalled, the original propeller was removed and a serviceable propeller was installed to facilitate an engine ground run. The airplane's fuel tanks contained 100LL fuel which was utilized during the test run.

A fuel test pressure gauge was used to check the fuel pressure. All tested pressures were within limits. The engine run-up was normal. The following indications were noted: oil temperature, 100; oil pressure, 68 psi; magneto drop on the right, 50 rpm; magneto drop on the left, 50 rpm; the carburetor heat check produced a drop in rpm. The maximum rpm was 2,200 rpm. No operational anomalies to preclude normal operation were noted.

Using a Safety Board computer program and the weather conditions recorded on the automated weather observation system (AWOS) at Grass Valley, the density altitude was calculated to be 6,273 feet mean sea level at the time of the accident. Temperatures throughout the day ranged from 81-99 degrees Fahrenheit. At the time of the accident, the temperature was 96 degrees Fahrenheit.

According to FAA publication Advisory Circular (AC) AC 65-12A, fuel normally remains in a liquid state until it is discharged into the air stream and changes into a vapor. Under certain conditions the fuel may vaporize in the lines, pumps, or other fuel components. The vapor pockets formed by the premature vaporization can restrict the fuel flow through units that were designed to handle liquids rather than gases. The resulting partial or complete interruption of the fuel flow is called vapor lock.

The AC further states that transfer of heat from the engine tends to cause vaporization of fuel in the lines and the pump. This tendency is increased if the fuel in the tank is warm, commonly as a result of high atmospheric temperatures. Vapor lock can become serious enough to block the fuel flow completely and stop the engine. Even small amounts of vapor in the inlet line can restrict the fuel flow to the engine driven pump and ultimately reduce its output pressure.

NTSB Probable Cause

The loss of available engine power due to vapor lock. A contributing factor was the high temperature.