What happened
Approximately 30 minutes before starting the engines, the crew initiated the auxiliary power unit (APU) sequence. The aircraft was occupied by the crew and four passengers. During the start of the number 2 engine, a smell of smoke was detected within the cabin. Upon observing smoke, the crew immediately shut down the number 2 engine, the APU, and all electrical switches. All occupants successfully evacuated the aircraft via the main cabin door and were not injured.
The investigation
An inspection of the aircraft revealed that a venturi fan unit motor, positioned aft of the rear cabin bulkhead, had overheated and failed. This failure resulted in charred components and wiring in the immediate vicinity of the venturi. No other anomalies were identified during the inspection.
Findings
Investigators determined that the cause was the failure of a venturi fan unit motor. It was noted that this specific venturi was an older model previously identified in 1994 as being susceptible to fan motor overheating. While a 1994 Airworthiness Directive (AD) required inspections of these older units every four years, the unit installed on this aircraft had been in service since 1999.