Pilot Debrief

GRUMMAN AIRCRAFT G-164A near Hazelton, ID — 2011-05-28

Final reportWPR11LA238
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Date
2011-05-28
Location
Hazelton, ID, USA
Airport
U94
Aircraft
GRUMMAN AIRCRAFT G-164A
Registration
N9724
Category
Airplane
Highest injury
None
Fatalities
0
Phase of flight
Climb

Probable cause

A total loss of engine power during low-level maneuvering due to an excessively worn carburetor.

NTSB narrative

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.

Analysis

Primary failure mode
Engine power loss
First missed decision gate
Pilot could have performed an emergency landing sooner after engine began losing power.

NTSB coding

Evidence available

  • Photos
  • 11 docket documents
View NTSB final reportView NTSB docket

Docket documents11

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