NTSB Factual Report

HISTORY OF FLIGHT

On May 14, 2005, about 1030 Pacific daylight time, a Great Lakes 2T-1A-2, N765GL, collided with the runway surface during an aborted takeoff following a partial loss of engine power at the Sonoma Valley Airport, Schellville/Sonoma, California. The pilot/owner was operating the airplane under the provisions of 14 CFR Part 91. The private pilot, the sole occupant, sustained minor injuries; the airplane sustained substantial damage. The personal local area flight was originating from the airport at the time of the accident. Visual meteorological conditions prevailed, and a flight plan had not been filed.

During a telephone conversation with a National Transportation Safety Board investigator, the pilot stated that the purpose of the flight was to perform a series of touch-and-go practice takeoff and landings. Prior to departure, he completed an engine run-up. He observed no anomalies from the engine gauges or with the performance. The pilot positioned the airplane for takeoff on runway 25.

The pilot further stated that upon rotation, the airplane's engine began to surge and he noticed a subsequent degradation in climb performance. After reaching about 30 to 40 feet above ground level (agl), he realized the airplane would not be able to continue the departure and opted to perform an emergency landing on the alternate runway 17. He maneuvered the airplane in a left turn and attempted to align with the runway. The airplane collided with the runway surface in a 15-degree nose low attitude. The airplane incurred damage to both lower wings and landing gear.

AIRPLANE INFORMATION

The Great Lakes 2T-1A-2, serial number 0765, was manufactured in 1977. The most recent annual inspection was completed on December 22, 2004, at which time the airplane had accrued a total time in service of 741.81 hours. A Textron Lycoming AEIO-360-B1G6 engine, serial number L-16851-51A, was the original Great Lakes factory installed engine and had accumulated the same total time in service as the airframe. The engine's last annual inspection was accomplished on the same date noted for the airframe.

The pilot refueled the airplane with full fuel about 2 weeks prior to the accident. During his preflight inspection for the accident flight he did not sump the fuel tanks and used the cockpit gauges to confirm that the airplane had full fuel. According to Textron Lycoming's Key Reprints publication, it is "necessary to supply the engine with a steady, uninterrupted flow of fuel for all operating conditions. An effective continuous fuel supply is provided by use of the fuel boost pump. As a general recommendation, the fuel boost pump should be used with Lycoming engines in all conditions where there is any possibility of excessive vapor formation, or when a temporary cessation of fuel flow would introduce undesirable hazards." The conditions under which Textron Lycoming recommends operation of the fuel boost pump include "every takeoff."

METEOROLOGICAL INFORMATION

An Automated Surface Observation System (ASOS) at the Napa County Airport (APC), Napa, California (located about 8 nautical miles east from the accident site), generated a routine aviation weather report (METAR) at 1054. It reported: winds from 210 degrees at 8 knots; temperature 71 degrees Fahrenheit; dew point 59 degrees Fahrenheit; and altimeter 30.02 inHg.

TESTS AND RESEARCH

A Federal Aviation Administration (FAA) inspector examined the airframe and engine at the accident site. He noted no anomalies or preimpact mechanical malfunctions with the airplane.

An airplane mechanic, who also holds an Inspection Authorization (IA), examined the wreckage on June 06, 2005. He stated that he tested both the right and left magneto, obtaining spark from each unit. The gascolator bowl and screen were clean from debris. The forward alternate air door appeared to be functioning correctly. The door below the injection servo was impact damaged. A disassembly of the engine driven fuel pump revealed that all check valves were intact. He did not operationally test the boost pump but noted that the by-pass was working. The boost pump switch in the cockpit was set to the "off" position. The throttle body was broken at the mounting flange and had a silicon diaphragm installed; no defects were noted. The fuel injectors were all free from debris and uniformly inscribed with the letter "A."

The fuel lines were inspected and no obstructions were found. All of the connections were tight and residual fuel was found throughout the lines. No water or contaminates were observed in the fuel system. The injection manifold vent was observed in the open position. There were no obstructions to the intake or exhaust manifold.

The spark plugs were removed and examined. All but one spark plug had a thin residue film, which the mechanic attributed to being consistent with a rich fuel mixture. The bottom spark plug on the number four cylinder was oil coated. All of the cylinder barrels and piston heads were coated with a black residue, which the mechanic stated was also indicative of a rich fuel mixture.

The mechanic removed the cylinders and rotated the engine crankshaft, noting no anomalies. The crankshaft turned freely and the camshaft was timed adequately. The magneto drive gears and the engine driven fuel pump plunger appeared to be functioning normally. The mechanic stated that he did not find anything that would have precluded the engine from normal operation.

The fuel servo was sent to Precision Airmotive and examined under the auspices of a National Transporation Safety Board investigator. The external examination revealed that the unit showed wear from a black coloration in the throat section and blue staining present near the idle valve. Due to damage to the body, the unit was tested via a metering suction differential (MSD) field bench. During the testing investigators noted several small fuel leaks at the idle valve, fuel diaphragm, and center body seal.

Several flow tests were conducted a different operating points. At an airflow of 600 pounds per hour (pph) the predetermined flowmeter limits for applicable model servo are a minimum of 51.7 pph and a maximum of 58.8 pph. The accident unit's flow tested at 77.2 pph. At an airflow of 1,000 pph the flow minimum is 83.8 pph with a maximum of 95.4; the accident unit tested at 102.5 pph.

ADDITIONAL INFORMATION

The elevation at the accident site was about 10 feet mean sea level (msl).

A representative from Textron Lycoming stated that based on the fuel servo's tested flow, the engine would most likely not be able to produce normal power at sea level altitudes. He additionally reported that it was possible that the accident engine failed to produce adequate power for departure due to the excessive fuel flow and resulting rich mixture.

A representative from Precision Airmotive stated that the fuel servo (part number 2524682-1) was originally manufactured between 1976 and 1977. He reported that the accident unit did not appear to have ever been overhauled and had the original manufacturer tag affixed to its body. A review of the engine logbook revealed that no entries were made regarding a fuel servo overhaul.

Precision Airmotive issued Service Bulletin PRS-97, recommending overhaul requirements for fuel servos that are utilized on general aviation aircraft. It states that the time between overhaul (TBO) requirements for the servo is the same as the TBO specified by the engine manufacturer; or 10 years since the unit was placed in service or at the last overhaul, which ever occurs first.

NTSB Probable Cause

a partial loss of engine power, which resulted from the fuel servo leaking and generating an excessively rich fuel/air mixture. A factor was the owner's failure to comply with a service bulletin.