On October 26, 1983, an Enstrom F28F (registration N8621X) was involved in an aviation accident near Chino, CA. Investigators recorded the probable cause as: In-flight separation of a clamp (Enstrom P/N LW 13464) securing the turbocharger to its exhaust pipe, which failed at a spot weld. Hot exhaust gases burned the cowling, buckled the firewall, and ignited material in the cockpit. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
An aircraft experienced an in-flight fire during a flight test after routine maintenance. The pilot made an emergency landing, but the onboard fire extinguisher was ineffective. Investigation revealed a clamp failure led to the fire.
Incident
During a flight test following routine maintenance, the aircraft experienced an in-flight fire while on the downwind leg of the traffic pattern. The pilot reported smoke entering the cockpit at 500 feet above ground level, with all gauges and systems appearing normal. As the smoke increased, the pilot executed an emergency landing on the ramp. After touchdown, the pilot requested fire department assistance via the tower. A passenger attempted to use the onboard fire extinguisher, discharging it on the fire, but it did not extinguish the flames. Fire department personnel arrived and extinguished the fire approximately two minutes later without difficulty.
Investigation
Investigation revealed that a clamp (Enstrom part number LW 13464) securing the turbocharger to its exhaust pipe had separated in flight. This allowed hot exhaust gases to burn the cowling and cause the firewall to buckle. The heat subsequently ignited material in the cockpit. Examination of the clamp showed that it had failed at a spot weld. The manufacturer of the aircraft's fire extinguisher described its chemical agent as ineffective against aluminum or magnesium fires, which are common in aircraft structures.
Findings
The investigation determined that the in-flight fire originated from the separation of the turbocharger exhaust pipe clamp due to a spot weld failure. The fire spread to the cockpit via heat from the exhaust gases. The onboard fire extinguisher's lack of effectiveness against metal fires contributed to the inability of the passenger to suppress the fire before the fire department arrived.
Probable cause
In-flight separation of a clamp (Enstrom P/N LW 13464) securing the turbocharger to its exhaust pipe, which failed at a spot weld. Hot exhaust gases burned the cowling, buckled the firewall, and ignited material in the cockpit.