Amateur-built SPORT HORNET N72PD accident near Mariposa, California

Probable cause

Improper clearance and inadequate heat shielding between engine components and the exhaust system, which resulted in an in-flight fire.

NTSB analysis

The pilot was returning to the airport when he noticed the smell of smoke in the cockpit. The smoke intensity increased, and after about 15 seconds, he opted to perform a forced landing into a pasture. During the landing roll, the nosewheel separated from the airplane, which slid to a stop. The pilot stated that after egressing, he observed fire emanating from underneath the engine area.

A postaccident examination revealed that the engine’s predominant area of thermal deformation was around the No. 4 cylinder (right side). Examination of the bottom of the engine revealed that the right side exhibited hotter thermal exposure signatures than the rest of the engine. Due to the thermal destruction, it could not be determined precisely where the fire originated; however, the area where the damage was the greatest was where the fuel lines, coolant lines, ignition harness, and carburetor were located. It was also noted that no heat shielding was installed between the exhaust system and the engine, which more than likely had an effect on the initiation of the fire.

Both the engine and the exhaust manufacturers recommended installing heat shielding between the exhaust and engine components. The limits section of the Installation Manual states that if there is not proper heat shielding to protect the modules and fuel lines from the exhaust heat, the engine may be susceptible to a fire. However, because this airplane is experimental, there is no requirement for the installation of the heat shield.

Text from the NTSB. Open the NTSB docket for WPR12LA113 for the full record.