N6799KGrumman Acft Eng Cor-Schweizer G-164B · 1979

On January 30, 2010, about 1030 Pacific standard time, a Grumman G-164B, N6799K, nosed over in an open field during a forced landing about one minute after taking off from Pullman-Moscow Regional Airport, Pullman, Washington. The commercial pilot was not injured, but the airplane, which had just been purchased by Pleasant Valley Aviation, American Falls, Idaho, was substantially damaged. The local pre-ferry familiarization flight was being conducted under 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed in the area of the accident. No flight plan had been filed.

According to the pilot, just about the time he passed the end of the runway at about 150 feet above ground level (agl), the airplane's engine began to lose power. Because he did not have enough power to keep the airplane airborne, the pilot maneuvered to land in an open field of freshly planted winter wheat. Although the touchdown was successful, during the landing roll on the soft rough terrain, the main landing gear wheels began to sink into the dirt, and the airplane nosed over onto its top wing. During the nose-over sequence the airplane's wing structure was substantially damaged.

During a post-accident inspection of the airframe and engine, it was discovered that a bird's nest had been sucked from the carburetor heat warm air pickup ducting, upstream from the carburetor heat valve, and lodged in the carburetor intake screen, cutting off a significant portion of the induction air flow. Further discussions with the pilot determined that due to the cold temperatures on the morning of the flight, he followed the “Cold Weather Engine Operation” procedures in the Ag-Cat pilot handbook. Because those procedures called for the engine oil and cylinder head temperatures to reach a minimum level before takeoff, the pilot had run the engine on the ground for about 30 minutes prior to performing the pre-takeoff run-up check. During that check he exercised the carburetor heat system, which worked as prescribed. It is thus surmised that during the long run-up, the bird’s nest became dislodged and was sucked into the area near the carburetor inlet screen during the carburetor heat test. The condition of the nest remains indicated that during the increased volume and velocity air flow during takeoff, the nest partially disintegrated and ultimately covered a significant portion of the inlet screen surface (see docket photo).

According to the Federal Aviation Administration (FAA) Inspector who monitored the airframe and engine inspection, the nest was located up inside the warm air pick up ducting, which is an area that the pilot would not normally see up into or check unless there was external visual evidence to indicate the need for a further inspection.