WPR09LA179

The airplane used for the skydiving operation was equipped with a foot step just above the right wheel, which the skydivers used to launch from the airplane. As the last of four skydivers stepped on the foot step, the right main landing gear fell away. The pilot reported that after he flew around for about 1 1/2 hours to burn off fuel, he intended to perform a low pass over the runway before coming around to land. The carburetor heat was turned on during the descent and, as he applied power to go around at midfield, the engine sputtered and lost partial power. The airplane was about 20 feet above ground level and he was able to maintain that altitude past the runway end before landing off the runway surface on snowy terrain. The airplane subsequently nosed over and came to rest inverted, sustaining substantial damage to both wings and the empennage. The carburetor heat was found in the “off” position; however, the investigation did not determine if the pilot turned off the carburetor heat or if it was pushed in by impact forces. Examination of the main landing gear revealed a fracture originating at the forward upper surface spring. The fracture surface displayed features indicative of fatigue cracking; the depth of the cracking was approximately 0.11 inches. An examination of the engine and carburetor revealed no anomalies that could account for the loss of partial power. The meteorological conditions were not conducive to carburetor icing.

HISTORY OF FLIGHT On April 4, 2009, at 1521 mountain daylight time, a Cessna 182, N6433A, nosed over during an off airport forced landing at Carson Field Airport, Kalispell, Montana. The owner was operating the airplane under the provisions of 14 Code of Federal Regulations (CFR) Part 91. The certificated commercial pilot was not injured; the airplane sustained substantial damage to the wings and empennage. The local skydiving flight departed Kalispell City Airport about 1330. Visual meteorological conditions prevailed, and no flight plan had been filed. The pilot departed with four skydivers on board. The airplane was equipped with a foot step just above the right wheel, which the skydivers used to launch from the airplane. They flew to the jump zone, and as the last skydiver stepped on the foot step, the right main landing gear fell away. After flying about 1 1/2 hours to burn off fuel prior to landing, the pilot elected to divert to the airplane’s home base at Carson Field. He reported that he intended to perform a low pass, and then come around for landing. He stated that he overshot the runway centerline, and used a slip maneuver to get back into position. He stated that he had the carburetor heat turned on during the descent. As he applied power to go around, the engine sputtered in a fashion that he described as just like carburetor ice. METEOROLOGICAL INFORMATION An aviation routine weather report (METAR) for Kalispell was issued at 1455 MDT. It stated: winds calm; visibility 10 miles; skies, few at 5,000 feet; temperature 9/48 degrees Celsius/Fahrenheit; dew point -7/19 degrees Celsius/Fahrenheit; altimeter 30.25 inches of mercury. The relative humidity was 32 percent. The weather conditions were plotted on the chart for the probability of carburetor icing depicted in FAA Special Airworthiness Information Bulletin (SAIB) CE-09-35. Their location fell outside the probability range for icing. ADDITIONAL INFORMATION WITNESS OBSERVATION A Safety Board investigator observed the accident. He heard the pilot apply power midfield at an estimated altitude of 20 feet above ground level (agl); the engine sputtered and the airplane maintained altitude. He continued to observe it fly at the same altitude past the runway end, sputtering intermittently, and then out of his view behind a hill. He did not observe any smoke or vapors emitting from the airplane. The airplane touched down off the runway surface on snowy terrain. It nosed over and came to rest inverted sustaining substantial damage to both wings and the empennage. The right main landing gear separated just inside the airframe. The fracture surface was flat, and granular in appearance. The investigator observed fuel leaking from the fuel caps after the accident, although the position of the airplane prevented an accurate assessment of the total fuel onboard. He observed fuel in the firewall mounted gascolator. The fuel had the appearance and smell of automobile gasoline. He noted that thefuel selector valve was in the off position, and the carburetor heat, fuel mixture, propeller, and throttle controls were in the full forward position. He confirmed that the carburetor heat control was continuous from the cabin through to the flapper located within the carburetor mounted heat box. METALURGICAL EXAMINATION Cessna examined the fractured right main landing gear (MLG) spring, part number 0741009-4, and the Safety Board Material’s Laboratory concurred with their findings. The fracture origin was at the forward upper surface of the MLG spring. They noted a chevron pattern on the fracture surface. Mechanical damage obscured any surface imperfections that may have been present prior to the fracture. Under high magnification, the fracture surface showed features indicative of fatigue cracking; the depth of the cracking was approximately 0.11 inches. ENGINE EXAMINATION An engine repair facility disassembled and examined the engine. They discovered no defects with the engine or carburetor. They reassembled the engine, and reinstalled the carburetor. During a ground test run, they stated that the engine and carburetor functioned properly.