SCHWEIZER AIRCRAFT CORP G-164B near Tracy, CA — 2021-07-30

Probable cause

A loss of thrust during a low-level agricultural application flight, which resulted in a descent and impact with terrain. The reason for the loss of thrust could not be determined based on available information.

NTSB narrative

The pilot reported that he was performing a low-level agricultural pesticide application on a hay field when the engine suddenly lost all power. Although the airplane was at a high airspeed at the time, the pilot was unable to climb due to the presence of high-tension powerlines above him in his flightpath. During the subsequent descent, he flew beneath a set of powerlines, turned, and landed in a field after his airspeed had decreased. During the landing, the airplane contacted the ground and trees, which resulted in substantial damage to the fuselage and wings. Postaccident examination of the engine and accessories did not reveal any mechanical anomalies that could have precluded normal operation. Evidence of rotational scoring and metal spray deposits in the engine indicate that it was operating at the time of impact. The fuel solenoid shutoff valve was in the CLOSED position, which would have prevented fuel flow to the engine. However, due to the overwhelming evidence that the engine was rotating at the time of impact, it is likely that the shutoff valve moved to the CLOSED position as a result of the impact. Propeller signatures indicated that the blades impacted the ground while rotating at low power. An examination of the propeller did not reveal any visible discrepancies that would have affected performance prior to impact. The damage to the start lock brackets, start lock plates, and a contact mark on the internal surface of the piston suggest the propeller was on or below the start lock angle at impact. This was likely the result of impact forces, as the pilot stated that he did not reduce throttle input or attempt to feather blades before impact. Previous maintenance indicated that the blade radius was properly set. The pilot did not recall the power lever position at the time of the power loss and the investigation did not reveal any evidence of preimpact mechanical malfunctions or failures. Therefore, the reason for the pilot’s reported loss of power could not be determined.

Analysis

Primary failure mode

Engine power loss

First missed decision gate

Pilot could have chosen a different flight path to avoid power lines.

NTSB coding

• Unknown or undetermined · Emergency descent

Evidence available

• 10 docket documents

Docket documents10

• PILOT/OPERATOR AIRCRAFT ACCIDENT REPORT, NTSB FORM 6120.1form
• RELEASE OF AIRCRAFT WRECKAGE, NTSB FORM 6120.15form
• STATEMENT OF PARTY REPRESENTATIVES TO NTSB INVESTIGATIONform
• AIRCRAFT LOGBOOKSother
• EMAIL CORRESPONDENCE WITH ACCIDENT PILOTother
• PROPELLER MAINTENANCE RECORDSother
• FUEL CONTROL UNIT FUNCTIONAL TEST REPORTreport
• MANUFACTURER PROPELLER EXAMINATION REPORTreport
• MEMORANDUM FOR RECORD, HONEYWELL ENGINE TEARDOWN REPORT EXCERPTreport
• WOODWARD PROPELLER GOVERNOR FUNCTIONAL TEST REPORTreport

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