What happened
On February 21, 2002, at 12:06 local time, a PIPER PA-28-161, registration EC-GFH, was parked at the Cuatro Vientos Airport apron preparing for a flight training mission. The aircraft was occupied by an instructor and a student pilot.
During the engine start sequence, the student pilot attempted to start the engine. After several unsuccessful attempts, the instructor suspected the engine was flooded and directed the student to follow the manual's procedure for a flooded engine. During this process, smoke and a burning odor were detected inside the cabin. The instructor instructed the student to evacuate the aircraft and followed the manufacturer's emergency procedures for an engine fire during start-up.
Upon exiting, the crew observed large flames exiting the exhaust. The fire was extinguished using a fire extinguisher from a nearby fuel tanker truck, which the instructor chose to use because the aircraft's onboard extinguisher was deemed insufficient. The occupants of the aircraft were uninjured.
The investigation
The investigation established that the student pilot had initially followed the "cold start" procedure. After the engine failed to start, the instructor transitioned to the "flooded engine" procedure. Post-incident inspections of the PIPER PA-28-161 revealed that the air filter had sustained fire damage. While fuel leaks were present in the engine compartment, investigators found no evidence that these leaks were the cause of the fire, nor were there any electrical malfunctions identified.
Investigators noted that the aircraft's manual specifies that if the engine does not start within 10 seconds, the pilot should prime and retry. However, the manual does not explicitly state the maximum number of permitted attempts before switching to the flooded engine procedure, which involves engine ventilation.
Findings
- Repeated start attempts led to the accumulation of fuel, partly in vapor form, within the engine intake.
- The primary cause of the incident was a carburetor explosion occurring during one of the start attempts.
- The incident might have been avoided if the flooded engine procedure had been implemented sooner.
- There is a need for more detailed start-up procedures to reduce pilot discretion regarding when to switch between different starting methods.