What happened
During a flight conducted under Part 91 regulations, a crew consisting of a captain and a co-pilot was operating an icing research equipped airplane to identify icing conditions for helicopter prototype testing. While cruising through instrument meteorological icing conditions, the aircraft accumulated approximately one inch of ice on its wing leading edges. The captain engaged the pneumatic deicing boots, which successfully cleared ice from the outer portions of the wings.
Approximately four minutes following the activation of the deicting boots, both engines experienced a simultaneous loss of all power. Despite multiple attempts by the crew to restart the engines, the aircraft was unable to maintain flight and performed a forced landing on snow-covered, frozen terrain. The impact with several small, burned trees resulted in substantial damage to the aircraft. There were no reported fatalities, though the aircraft sustained significant structural damage.
Findings
Investigation into the engine failure revealed catastrophic damage to the power plants, which was consistent with the ingestion of ice. The aircraft utilized two distinct ice protection systems: pneumatic boots for deicing the outer wing surfaces and a heated anti-ice system for the inboard sections and engine inlets. Unlike the deicing boots, the heated anti-ice system requires manual activation by the crew before entering icing conditions.
Evidence from onboard photographs showed that ice had accumulated on the heated inboard sections of the wings prior to the deicing boots being activated. While the boots cleared the outer wings, the ice remained on the heated segments. The crew did not utilize a checklist regarding the anti-ice system and could not confirm if the system had been activated. Because the anti-ice system requires several minutes to reach an effective temperature, the failure to activate the anti-ice system prior to ice accumulation allowed ice to remain on the engine inlets, leading to the engine failure.