Incident Overview
The accident involved a scheduled cargo flight operating from Nanaimo, British Columbia, to the civilian terminal on the south side of the military airbase at Comox, British Columbia. The flight was conducted under visual meteorological conditions. Both crew members were fatally injured when the aircraft crashed.
Sequence of Events
During the approach, the crew established communication with Comox tower while at approximately 2,000 feet over Hornby Island, about 12 nautical miles southeast of Comox. They requested and received approval for a practice back course/localizer approach to Runway 30, with a circling approach for landing on Runway 18. As the aircraft proceeded inbound and reached about two miles from the threshold of Runway 30, the crew declared an emergency due to an engine fire in the right engine. The tower immediately alerted airport response teams and requested standard data from the crew, including the number of people and fuel on board.
Less than 30 seconds after the initial emergency report, the aircraft became engulfed in flames. Shortly thereafter, at 0741 Pacific daylight time, the aircraft rolled inverted and struck the ground in a steep, nose-down, left-wing-low attitude. The impact caused the aircraft to break apart and burn.
Probable Cause
The official investigation identified the following causes and contributing factors: A bad gasket (P/N LW-13388) had been installed in the accident engine at some point after April 1, 1999. The requirement of Airworthiness Directive 2002-12-07 was not carried out on the accident engine, which mandated the removal and replacement of old converter plate gaskets. The improper oil filter converter plate gasket in the right engine compartment failed, allowing pressurized oil to spray onto hot turbocharger and exhaust components, igniting the fire. The firewall fuel shut-off valve remained in the OPEN position, which permitted pressurized fuel to be delivered to the engine-driven fuel pump. The initial oil-fed fire generated heat that melted the fuel pump casing, causing pressurized fuel to intensify the fire. The flames then breached the main fuel tank inboard of the engine, leading to the aircraft being engulfed. Additionally, the investigation noted as risk factors that inappropriate converter plate gaskets (P/N LW-13388) remained in the aviation system after the AD terminating action, and compliance with the full AD requirements, including vibro-peening and proper gluing procedures, was not always achieved.