On June 8, 1990, a Grumman-schweizer G-164B (registration N6725K) operated by Vince Crop Duster, Inc. was involved in an aviation accident near Buttonwillow, CA. Investigators recorded the probable cause as: FAILURE OF THE #7 CYLINDER DUE TO A PRE-EXISTING CRACK. THE TERRAIN CONDITION WAS A RELATED FACTOR. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During an aerial application swath run, the pilot heard a loud backfire and the engine quit. Attempting a landing on a dirt road, the aircraft landed short in a tomato field and nosed over. Examination revealed a cracked number 7 cylinder head with contamination indicating the crack existed for a lengthy period.
Incident Overview
While completing an aerial application swath run, the pilot heard a loud backfire emanating from the engine during the pull-up. Immediately thereafter, the engine quit running altogether. The pilot attempted to make a landing on a dirt road but landed short in a tomato field, causing the aircraft to nose over onto its back.
Engine Examination
A post-accident examination of the engine revealed that the number 7 cylinder head had a crack. The crack extended from the forward spark plug boss around the cylinder head to the rear spark plug boss. A detailed examination of the crack showed that the fracture face was contaminated by carbon deposits and light corrosion in the coarse area of the crack, indicating that the crack was present for a lengthy period of time prior to the accident. The cylinder was reported to have only 181 hours since overhaul.