Wamsutter, WY, USA
N794CH
Sharp Corben Baby Ace D
The airplane was being ferried to its new owner. The pilot said he was cruising at 8,000 feet msl (1,000 feet agl), using a power setting of 2,400 rpm with the mixture leaned "for altitude." About 1 hour after takeoff, the engine began "sputtering and backfiring." Engine power dropped from 2,400 rpm to approximately 1,000 to 1,100 rpm. Unable to restore power, the pilot made a forced landing on rough, uneven terrain. During the landing roll, the airplane struck a hole and nosed over, coming to rest inverted. The accident site was at an elevation of 6,955 feet msl. The pilot told a sheriff's deputy that "it was either engine failure or [the] carburetor iced up." Temperature and dew point recorded at an automated weather observation station (AWOS) station, located 48 miles east of the accident site, were 4 degrees and 0 degrees C., respectively. According to the Carburetor Icing Probability Chart, the temperature and dew point correspond to "serious icing at cruise power." The computed relative humidity was 76 percent. The pilot said he had had "carburetor ice before and the onset was always a gradual onset of power loss requiring changes in the throttle setting until ice was recognized. This was NOT the case in this incident as the power loss was instant and no actions affected it after they were tried." According to FAA's Flight Training Handbook, the onset of ice may be subtle or sudden, particularly if ice forms on the carburetor jets, because it "tends to choke off the flow of air and reduce the power output, or even prevent the engine from operating." The engine was functionally tested to 2,100 rpm, and no discrepancies were noted. Additional power output was not possible due to the intake manifold being crushed during the accident.
On September 18, 2003, approximately 1230 mountain daylight time, a Sharp Corben Baby Ace D, N794CH, was substantially damaged during a forced landing after the lost power near Wamsutter, Wyoming. The commercial pilot, the sole occupant, sustained minor injuries. Visual meteorological conditions prevailed, and no flight plan had been filed for the ferry flight being conducted under Title 14 CFR Part 91. The flight originated at Rock Springs, Wyoming, at 1140. The airplane was being ferried from Susanville, California, to Evansville, Indiana. The pilot discussed weather conditions along his intended route with other pilots before his departure, and monitored the Rawlins AWOS (Automated Weather Observation Station) frequency. He was cruising at 8,000 feet msl (1,000 feet agl), using a power setting of 2,400 rpm with the mixture leaned "for altitude." About 1 hour after takeoff, the engine began "sputtering and backfiring." Engine power dropped from 2,400 rpm to approximately 1,000 to 1,100 rpm. Unable to restore power, the pilot made a forced landing on rough, uneven terrain. During the landing roll, the airplane struck a hole and nosed over, coming to rest inverted. The accident site was at an elevation of 6,955 feet msl. According to the Sweetwater County Sheriff's Department report, the pilot said "it was either engine failure or [the] carburetor iced up." The pilot voluntarily submitted to an Alcohol Breathalyzer Test. The results were negative. At 1153, the Rawlins AWOS recorded the following weather observation: Wind, 280 degrees at 12 knots; visibility, 10 statute miles or greater; sky condition, clear; temperature, 4 degrees Celsius; dew point, 0 degrees Celsius; altimeter setting, 30.35 inches of mercury. According to the Carburetor Icing Probability Chart, the temperature and dew point correspond to "serious icing at cruise power." The computed relative humidity was 76 percent. In his accident report the pilot wrote, "I have had carburetor ice before and the onset was always a gradual onset of power loss requiring changes in the throttle setting until ice was recognized. This was NOT the case in this incident as the power loss was instant and no actions affected it after they were tried." The onset of ice may be subtle or sudden, particularly if ice forms on the carburetor jets. According to FAA's Flight Training Handbook, ice "tends to choke off the flow of air and reduce the power output, or even prevent the engine from operating." On November 5, 2003, the engine was functionally tested to 2,100 rpm, and no discrepancies were noted. Additional power output was not possible due to the intake manifold being crushed during the accident. Airplane damage consisted of a bent main landing gear, crushed vertical stabilizer and rudder, both wings bent down at the roots, and a cracked engine cowling.
A loss of engine power due to carburetor icing. Contributing factors were weather conditions conducive to carburetor icing and unsuitable terrain available on which to make a forced landing.
Source: NTSB Aviation Accident Database
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