History of Flight
On January 30, 2010, at about 1030 Pacific standard time, a Grumman G-164B agricultural aircraft, registration N6799K, nosed over in an open field during a forced landing. The event occurred about one minute after departure from Pullman-Moscow Regional Airport in Pullman, Washington. The flight was a local pre-ferry familiarization flight being conducted under 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no flight plan had been filed.
Pilot Actions and Sequence of Events
The commercial pilot reported that as the airplane passed the end of the runway at approximately 150 feet above ground level, the engine began to lose power. Unable to maintain altitude, the pilot maneuvered for a forced landing in an open field of freshly planted winter wheat. The touchdown was successful, but during the landing roll on the soft, rough terrain, the main landing gear wheels sank into the dirt, causing the airplane to nose over onto its top wing. The wing structure was substantially damaged during the nose-over.
Post-accident Inspection
A post-accident inspection of the airframe and engine revealed that a bird's nest had been sucked from the carburetor heat warm air pickup ducting, upstream from the carburetor heat valve, and had lodged in the carburetor intake screen, significantly restricting induction air flow. The nest was located in an area that a pilot would not normally see or check unless external visual evidence indicated a need for further inspection, according to the Federal Aviation Administration Inspector who monitored the inspection.
Pre-flight Procedures
The pilot stated that due to cold temperatures on the morning of the flight, he followed the “Cold Weather Engine Operation” procedures in the Ag-Cat pilot handbook. These procedures required engine oil and cylinder head temperatures to reach a minimum level before takeoff, so the pilot ran the engine on the ground for about 30 minutes prior to performing the pre-takeoff run-up check. During the run-up, he exercised the carburetor heat system, which functioned as prescribed. It is surmised that during the long run-up, the bird’s nest became dislodged and was drawn toward the carburetor inlet screen during the carburetor heat test. The condition of the nest remains indicated that during the increased air volume and velocity during takeoff, the nest partially disintegrated and ultimately covered a significant portion of the inlet screen surface.
Injuries and Damage
The commercial pilot was not injured. The airplane, which had been recently purchased by Pleasant Valley Aviation of American Falls, Idaho, sustained substantial damage to its wing structure.