Incident Overview
On April 26, 2009, at approximately 0415 eastern daylight time, a Douglas DC3, registration N136FS, operated by Four Star Aviation Inc., was substantially damaged following a cockpit fire that occurred while taxiing at Luis Munoz Marin International Airport (TJSJ) in San Juan, Puerto Rico. The flight was a cargo operation under 14 Code of Federal Regulations Part 135, with a planned destination of Cyril E King Airport (TIST) in Charlotte Amalie, United States Virgin Islands. Visual meteorological conditions prevailed, and a company flight plan was filed. The crew consisted of a certificated airline transport pilot, a certificated commercial pilot, and two crewmembers, all of whom were not injured.
According to the flightcrew, they were transporting mail and taxiing on Juliet taxiway toward runway 10 when the instrument panel and cockpit floor erupted in flames, filling the cockpit with smoke. As the pilots initiated engine shutdown, they became overwhelmed by the fire and smoke and quickly exited the aircraft along with the two cargo handlers. The crew reported no abnormal instrument readings or anomalies during the preflight inspection.
Aircraft Information
The low-wing, tailwheel-configured Douglas DC3, serial number 22405, was manufactured in 1942. It was powered by two Pratt and Whitney R-1830-90D engines, each rated at 1,200 horsepower. At the time of the accident, the aircraft was configured for cargo with five seats. It had accumulated 19,952 total hours of operation.
Fire Damage Inspection
Examination of the wreckage by Federal Aviation Administration (FAA) inspectors revealed that the fire was intense, extending from the bulkhead behind the pilots' seats to the front of the aircraft. All instruments, switches, tubing, hoses, and skin in that area were melted. The damage was more pronounced on the right side of the fuselage. The left propeller was observed partially feathered.
Inspectors noted that the majority of wires inside the main junction box exhibited very little damage, except for two wires with missing insulation. The damage appeared related to the routing of these two wires, which were connected to the battery relay and ran through wires near exposed terminal studs. Heat damage was found on the insulation of wires and components in contact with the exposed wires. From the battery relay, the wires ran to the forward section of the cockpit where the fire originated. Due to the fire damage, inspectors could not determine which systems the wires served, but one system connected to the battery relay is the propeller feathering system.
Additionally, the fuel pressure system was a direct indicating system, with fuel traveling through rigid aluminum lines routed on the right lower side of the fuselage.
Maintenance Records
Review of maintenance records by FAA inspectors showed that the aircraft was maintained under an FAA Approved Airplane Inspection Program. The records indicated that the fuel pressure indicating system lines and hoses had never been replaced, but such replacement was only required on an as-needed basis.
The electrical system, instrument lines, and hoses through the nose compartment were required to be inspected during a Phase D inspection. The aircraft's last Phase D inspection was completed on July 14, 2008, after which it accrued 313.1 hours of operation until the fire. The most recent inspection was a Phase B inspection on March 22, 2009, with 40 hours of operation since then.
A search of the National Transportation Safety Board accident/incident database and FAA service difficulty reports for the five years preceding the accident revealed no similar events.