What happened
On 17 August 2006, a Piper PA-28-161, registration G-BGPJ, was performing a private local flight at Woodvale Airfield, Lancashire. During the landing roll following an unevent and local flight, the engine stopped twice. The pilot attempted to restart the engine, but after the second successful restart, the engine failed again.
While the pilot was discussing the engine issues with the passenger, a bystander alerted the crew to flames appearing around the nose landing gear leg. The pilot and passenger performed a rapid evacuation. The fire, which had caused damage to the engine fuel primer hose and some electrical wiring, was quickly extinguished using a foam fire extinguisher. There were no fatalities and no injuries to the crew or passenger.
The investigation
An investigation by the AAIB found moderate to severe fire damage in the lower engine bay. An engineering examination of the engine revealed that when the power was reduced to idle, the RPM dropped below normal, black smoke emerged from the exhaust, and the engine stopped. Fuel was also observed leaking from the carburettor air box.
Testing of the Marvel-Schebler/Precision Airmotive carburettor revealed that the fuel level in the float chamber was significantly above the maximum allowable limit. Upon inspection of the white plastic horseshoe-shaped float (part number 30-804), investigators discovered that one of the hollow arms was almost entirely filled with AVGAS. This was traced to a microscopic manufacturing defect in a hot-weld joint that allowed fuel to seep into the arm.
Findings
- A manufacturing defect in the 30-804 plastic float allowed AVGAS to enter the hollow arm.
- The presence of fuel in the float arm increased its weight, preventing the needle valve from closing fully.
- This resulted in an excessive fuel flow through the carburettor jets, creating a rich mixture that caused the engine to cut out at low power.
- The fuel leakage also caused fuel to overflow from the carburettor into the air box, which led to the fire.