Accident Details
On May 4, 2009, at approximately 1620 Pacific daylight time, a Grumman G-164B (registration N6628Q) collided with terrain during a forced landing at Colfax, Washington. The aircraft was operated under 14 CFR Part 133 for aerial application. The certificated commercial pilot, who was the owner, was not injured. The airplane sustained substantial damage to the firewall, fuselage, and empennage due to impact forces. Visual meteorological conditions prevailed, and no flight plan was filed.
The accident occurred during the 14th flight of the day. The pilot had fueled the airplane prior to the 13th flight. According to the pilot, the airplane was about 100 feet above ground level following takeoff when the engine lost power. The pilot executed a straight-ahead landing in a muddy dirt field. During the landing roll, the airplane nosed over, and the engine separated from the airframe.
Engine Examination
Gustin Aviation in Lewiston, Idaho, examined the engine under the supervision of an FAA inspector. The engine was not runable. Technicians installed it on a stand and removed the spark plugs. Gaps were similar with no mechanical deformation. Electrode colors varied: some gray indicating normal operation, others black and sooty suggesting excessive ground idle or rich idle mixture. Some back plugs had gray electrodes with lead fouling, and others were wet and oily. Manual rotation of the crankshaft was free, and valve lift was consistent. The oil sump screen and filter were debris-free. The FAA inspector reported no anomalies that would have precluded normal operation.
Carburetor Examination
The Safety Board investigator-in-charge oversaw examination of the Stromberg carburetor at S&T Aircraft Accessories in New Braunfels, Texas. The carburetor sustained substantial crush damage. Throttle shaft bushings were worn with excessive play. The pump stem bushing was also worn with excessive play, and the economizer linkage was loose. Fretting signatures were observed on the mating surface and mounting bolt holes. The carburetor fuel screen was clean, but the floats exhibited crush damage and the accelerator pump was worn.
Post-Accident Findings
Following the initial examination and release, the engine was sent to Covington Aircraft in Covington, Oklahoma, for a propeller strike inspection. The engine was repaired and returned to the owner, who installed it on the airplane. During a test flight, the engine ran rough, prompting the owner to return it to Covington for further examination. Technicians discovered a defective exhaust camshaft lobe and replaced it, which resolved the roughness. Covington reported that a defective camshaft lobe could cause roughness and, if ignored, might lead to multiple lobe failure and a loss of engine power. However, they noted that this particular lobe was not defective to that point and would not have been the cause of the reported loss of power. Covington believed that the carburetor was the reason for the loss of engine power.
No probable cause was stated in the investigation.