Cobb Aviation Services Beech 200 UNDESIGNAT accident

The Part 135 passenger flight was cleared for an instrument landing system (ILS) approach to the destination airport in marginal VFR conditions. Radar data showed the airplane intercept the final approach course, cross over the course, then re-intercept it several times as the airplane approached the airport. Throughout the approach, the airplane flew level at an altitude about 2,300 ft above ground level (agl) until about 2 miles from the runway threshold, when it began to descend. The airplane crossed the runway threshold about 650 ft agl and subsequently landed hard on the runway, resulting in substantial damage. The pilot stated that the hard landing was the result of an aerodynamic stall at a higher airspeed than normal due to ice accumulation on the wings. Two line workers observed ice on the leading edges of both wings after the airplane landed.

The operator's training manual stated that an approach that becomes unstabilized below 1,000 ft above airport elevation in instrument meteorological conditions or 500 ft above airport elevation in visual conditions required an immediate missed approach or go-around.

Icing conditions were widespread along the airplane's route of flight. These conditions had been forecast, and numerous pilot reports confirmed the presence of icing in the area. The extent to which the pilot had familiarized himself with the current and forecast weather conditions before the flight could not be determined. Although the airplane was approved for flight in icing conditions and equipped with deicing boots, the investigation could not determine if or when the pilot cycled the boots. The manufacturer's flight manual warned that, even after cycling the boots, ice accumulation could remain on protected and unprotected surfaces, resulting in significant increases in stall speed. The manual also advised that ice could affect the aural stall warning system, and that pilots should maintain a "comfortable margin" of airspeed above normal stall speed. The aggressive flare that was likely required to arrest the airplane's high rate of descent on final approach, combined with the airplane's higher stall speed due to ice accumulation, likely resulted in an aerodynamic stall and subsequent hard landing.

Verbatim NTSB analysis and probable cause from the NTSB dataset