Cessna 550 Citation II, Ft. Yukon, Alaska, Sept. 30, 2005–The captain, copilot and two research scientists were not seriously injured when Citation N77ND made an off-airport, gear-up emergency landing after both engines quit simultaneously. The University of North Dakota flight was doing icing research in IFR conditions when the accident occurred.
The captain told the NTSB that about seven-eighths of an inch of ice had accumulated on the wing leading-edge surfaces. He cycled the de-ice boots, then heard a loud “bang” at the rear of the airplane and both engines lost power. Descending, he tried to restart the engines. At about 3,000 feet above the ground, he abandoned restart attempts and concentrated on landing. The airplane’s wings, fuselage and empennage were damaged.
The Citation was operating as an icing scout for a helicopter manufacturer certifying a prototype helicopter for flight into known icing. It used on-board sensors to detect the appropriate icing conditions; the prototype helicopter would then fly into the icing.
The captain said that he operated the anti-ice equipment in accordance with the airplane’s flight manual and never intentionally flew the airplane in icing conditions with the icing equipment turned off. He said he saw the photographs the previous day of the parked airplane with ice buildup on the anti-ice surfaces, but he did not report a malfunction of the system.
An onboard representative of the helicopter company was monitoring test equipment in the rear of the airplane. He took photographs of both wings’ leading edges before the loss of power and before and after the de-ice boot activation. The before pictures show an accumulation of about one inch of ice on both the de-iced and anti-iced, inboard portion of the wing. The after pictures show the ice removed from the de-iced (booted) section of the wing, but the ice remained on the anti-iced, inboard portion of the win