The Transportation Safety Board (TSB) of Canada released its investigation report into the fatal October 2011 accident involving a Northern Thunderbird Air Beechcraft King Air A100, which crashed just short of a runway at Vancouver International Airport, Canada.
The investigation found that during routine maintenance, the left engine’s oil reservoir cap remained unsecured, and that this was not detected during the pre-flight inspection. During the climb-out, the crew noticed oil leaking from the left engine and elected to divert the flight back to Vancouver. While on the final approach, power was likely applied only to the right engine, causing the pilot to lose control of the aircraft as it rolled left, pitched down and crashed. Investigators found that the aircraft’s speed was below the speed needed to maintain directional control with low power on the left engine and high power on the right engine. The pilot reduced the right engine’s power and regained control; however, low altitude limited the recovery, and the aircraft collided with the ground. The aircraft was destroyed in a post-impact fire. All of the passengers were seriously injured, and both pilots succumbed to their injuries in hospital.
The investigation found that a non-mandatory modification to limit the loss of oil when the oil cap is left unsecured was not made to the aircraft’s engines. Additionally, multi-engine aircraft flight manuals and training programs do not include cautions and minimum control speeds for situations when one engine is at a low power setting and its propeller is not feathered (blades placed parallel to airflow to reduce drag). Operating below these unpublished speeds can lead to loss of control of the aircraft.
The investigation concluded that this was a survivable accident. However, a post-impact fire destroyed the aircraft, and the 2 pilots died from burn-related injuries. In this accident, there was evidence of live battery-powered circuits after impact, and fire in areas where wiring is concentrated in the cockpit. More needs to be done to reduce the risks associated with post-impact fires. The Board is therefore concerned that if no action is taken by Transport Canada to address the recommendations made in the TSB’s 2006 Safety Issues Investigation on Post Impact Fires Resulting from Small-Aircraft Accidents, ignition sources will remain, and the risk of post-impact fires will persist.
Following the accident, Northern Thunderbird Air provided information to its flight crews on the risk of flying with reduced power on one engine as speed decreases, and amended its standard operating procedures to reduce the risk of recurrence. Transport Canada is working with the engine manufacturer to increase implementation of the modification to limit oil loss from unsecured oil caps.