Accident Overview
On June 21, 2010, at 0825 central daylight time, a Cessna 525A, registration N800VT, sustained substantial damage following a runway excursion at Storm Lake Municipal Airport (SLB), Storm Lake, Iowa. The airplane was landing on runway 17, which measures 5,000 feet by 75 feet and is constructed of concrete. The airline transport pilot and five passengers were not injured. The flight was operated by Clausen Investments, Inc. under 14 Code of Federal Regulations Part 91 as a business flight.
Pilot Report
The pilot reported canceling the instrument flight rules flight plan and proceeding visually to the airport despite thunderstorms in the area. With wind reported from the south, runway 17 was selected. During the landing rollout, the wind shifted from a quartering headwind to a tailwind. The pilot was unable to stop the airplane on the runway due to the wet surface and wind conditions. The airplane departed the runway, and the nose gear and left main landing gear collapsed in grass and mud approximately 325 feet from the departure end. The pilot stated that less than 5,000 feet of runway was needed to stop, but with brakes fully applied, the aircraft responded as if it had none.
Investigation Findings
A Federal Aviation Administration (FAA) airworthiness inspector examined the airplane at the accident site with representatives from Cessna Aircraft. Tire pressures were within limits, and no chevrons, heat signatures, or skid indications were observed on the main gear tires. Brake fluid quantity and accumulator pressure were within limits. A ground test showed normal brake activation and anti-skid system operation. The anti-skid self-test functioned correctly, and the fault panel indicated no faults. Components from the anti-skid system—control box, control valve, and two transducers—along with the Enhanced Ground Proximity Warning System (EGPWS) were sent to the NTSB for further examination.
The EGPWS data download revealed only one data point recorded for the flight, corresponding to the airplane at 50 feet above the runway and approximately 950 feet from the pilot's reported touchdown point. The airplane's speed could not be determined from the data. The anti-skid components were tested functionally; all met requirements except one force vs. pressure test on the control valve, which was slightly below specifications. This condition was determined to have no effect on performance and was attributed to component age.
Weather and Runway Conditions
Visual meteorological conditions prevailed at the time, but thunderstorms were in the vicinity. Standing water was reported on the runway. The SLB Automated Weather Observing System (AWOS) was out of service. The 0815 observation at Cherokee County Regional Airport (CKP), 16 nautical miles west-northwest, reported wind 250 degrees at 7 knots, 10 miles visibility, light rain, broken ceiling 8,500 feet, overcast 11,000 feet, temperature 19°C, dew point 17°C, and altimeter 30.00 inches of Mercury.
Aircraft Performance Data
The pilot reported the gross weight at 10,200 pounds. The headwind component for runway 17 was 1 knot based on CKP data. The Airplane Flight Manual (AFM) provides landing distances for dry, wet, and water-covered runways. The AFM defines a wet runway as having sufficient moisture to appear reflective without significant standing water, and a contaminated runway as having more than 25% of the surface area covered by water more than 3 mm deep. Example AFM landing distances for 10,000 pounds and 1,000 feet pressure altitude at 20°C include: dry runway, 2,820 feet; wet runway (Vref), 4,050–4,350 feet; water-covered runway (0.125 inches), 5,900–6,250 feet. The 5,000-foot runway was available.