Amateur-built Harmon Rocket N275JS accident near Corona, California

Probable cause

A total loss of engine power during takeoff due to fuel starvation as a result of a failure of internal components of the fuel servo.

NTSB analysis

The private pilot, who was the owner and builder of the experimental amateur-built airplane, and a commercial pilot departed on a local flight and performed three touch-and-go practice takeoffs and landings. During the fourth takeoff, after reaching about 300 ft above the ground, the engine experienced a total loss of power. The airplane made a right turn and collided with terrain about 1,650 ft from the end of the runway. The single-engine airplane was constructed about 7 years before the accident, at which time the private pilot installed a newly-overhauled engine. The airplane had accrued about 100 total hours of time in service. During postaccident examination, the engine would not start but was found to operate normally when a different fuel servo was installed.

The Bendix fuel servo, manufactured in 1977, was designed to meter fuel in relation to the volume of air being consumed by the engine. The metering is accomplished by air and fuel diaphragms inside the unit that are connected by a valve stem that has a regulator ball affixed at its end. A pressure differential across the air diaphragm results in the regulator ball unseating and providing the engine with more fuel. Complete disassembly of the accident fuel servo revealed that the regulator stem was separated from the regulator ball, which would prevent the ball from being able to unseat and would subsequently block fuel from entering the engine, resulting in fuel starvation.

The servo manufacturer stated that the servo's internal components appeared to be original, although those components were required to be replaced every 12 years. There were no maintenance records pertaining to the servo, but its appearance indicated it was likely never overhauled. The maintenance entry for the engine overhaul noted that the airplane was equipped with a "serviceable fuel servo," which, according to a representative from the maintenance facility that performed the overhaul, was likely determined by an engine test run. Because the airframe and engine were classified as amateur-built experimental, the overhaul criteria are not required for airworthiness; however, it is likely that the failure of the regulator valve stem and ball would not have occurred if the servo components had been replaced in accordance with manufacturer specifications.

Text from the NTSB. Open the NTSB docket for WPR17LA054 for the full record.