NTSB Identification: WPR11LA238
14 CFR Part 137: Agricultural
Accident occurred Saturday, May 28, 2011 in Hazelton, ID
Probable Cause Approval Date: 07/18/2012
Aircraft: GRUMMAN AIRCRAFT G-164A, registration: N9724
Injuries: 1 Uninjured.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
The pilot was completing an aerial application pass over a field when the engine began to lose power. He initiated a climb, heard a bang, and observed a white puff of smoke issuing from the top of the engine. The engine subsequently lost all power, and the airplane sustained substantial damage during a forced landing into a pasture. Postaccident examination of the engine revealed that it did not exhibit catastrophic internal damage or any preimpact anomalies that would have precluded normal operation. The carburetor was undamaged during the accident and was subsequently installed on an exemplar engine for testing. During the tests, the engine sputtered, backfired, hesitated, and produced puffs of white smoke from the exhaust ports when the throttle was advanced from idle to power. The sputtering stopped when the throttle was advanced slowly. Examination and disassembly of the carburetor revealed excessive wear, particularly to the accelerator pump assembly. The accelerator pump provides increased fuel flow to the engine during rapid throttle advance, and an ineffective pump would cause engine hesitation and stumbling during acceleration. The symptoms reported by the pilot during what would have been rapid engine acceleration after completing a pass was consistent with a worn accelerator pump, and matched the engine characteristics observed during the carburetor test. The carburetor had been installed on another engine since its most recent maintenance event and its total time since overhaul could not be determined. The engine examination also revealed that five teeth from an intermediate gear within the supercharger drivetrain were fractured, with loading opposite of the direction of rotation. Metallurgical tests found that the teeth failed in overload. Given the rotational speeds of the supercharger system, the gear failure was most likely caused by the sudden engine stoppage after the propeller made contact with the ground.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: A total loss of engine power during low-level maneuvering due to an excessively worn carburetor. Full narrative available
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