Incident Overview
During cruise flight with the combustion heater operating, the pilot heard an explosion. Smoke entered the cabin, followed by a loss of electrical power. The pilot diverted the aircraft and landed without further incident.
Examination Findings
Post-flight examination revealed that the combustion heater had sustained heat and fire damage. The fuel pump supply line, located between the fuel pump and the heater, was found cracked at the fuel pump housing inlet and was loose. The fractured surfaces were dull and displayed carbon build-up.
Maintenance History
A review of the aircraft's logbooks indicated that on December 1, 1993, the combustion heater was removed, rebuilt, and re-installed at a total airframe time of 3,932.2 hours. No logged entries showed compliance with a 20-year-old Airworthiness Directive (AD) issued to "prevent a hazardous condition caused by deterioration on the combustion heater" for that specific heater model. The aircraft underwent an annual inspection in September 2001 at a total time of 5,213.5 hours. At the time of the event, the aircraft had accrued 5,231.9 total hours.