Grumman Acft Eng Cor-Schweizer G-164B N6799K accident near Pullman, Washington

Probable cause

A partial loss of engine power during takeoff due to a bird's nest being sucked into the induction air ducting.

NTSB analysis

Due to the cold temperatures on the morning of the flight, the pilot 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. During the long run-up, a 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. According to the Federal Aviation Administration inspector who monitored the engine inspection, the nest was located inside the warm air pick-up ducting, which is an area that the pilot would not normally see into or check unless there was external visual evidence to indicate the need for a further inspection.

Text from the NTSB. Open the NTSB docket for WPR10LA122 for the full record.