Piper PA28 N15417 accident near Knoxville, Tennessee

Probable cause

An in-flight fire that resulted from an inadequate 100-hr inspection, which failed to detect and correct improper electrical cable routing in the engine compartment.

NTSB analysis

When the flight instructor initiated a takeoff roll, the engine rpm initially increased to 2,200, then decreased to 800, followed by flames emanating from the engine cowling. The flight instructor rejected the takeoff, secured the engine, and exited the airplane on the runway; however, the fire continued in the engine compartment until airport personnel were able to extinguish it.

Postaccident examination of the engine compartment revealed that about a 25 to 30-in length of starter motor electrical lead was not clamped and had drooped down on top of the fuel primer line. Metal beads on top of the fuel primer line were consistent with chaffing and welding due to contact from the electrical lead. It is likely that arcing from the lead ignited fuel in the fuel primer line.

The airplane had been operated for 73 hours during a 1-month period following its most recent 100-hr inspection. The electrical lead drooping down and resting on top of the fuel primer line was contrary to Federal Aviation Administration (FAA) and aircraft manufacturer maintenance instructions regarding proper routing and should have been identified and corrected during the most recent 100-hr inspection.

Text from the NTSB. Open the NTSB docket for ERA23LA347 for the full record.