FTW96LA122

The pilot made a gliding approach to land from 3,500 feet MSL with the power set at 1500 to 1700 RPM and the carburetor heat on. The pilot reported to the investigator-in-charge that while descending through the first 3,000 feet that he did not clear the engine. The pilot recounted that the RPM began 'falling off', and when he increased the throttle, the RPM did not rise. The pilot performed a forced landing, but due to 'dusky conditions and slight haze', the pilot did not see a levee wall which the right wing impacted while in the landing flare. There was a temperature inversion at the time of the accident, with ground level humidity of 22% and a humidity of 49% at 5,000 feet. The FAA Flight Training Handbook states in the section under 'Descents (Maximum Distance Glides)' that during 'power-off descents, the engine should be cleared periodically to prevent excessive cooling and fouling.' The engine was test run on the airframe. According to the manufacturer, who performed the test run, the engine 'startup was immediate, and the engine ran smoothly.'

On February 16, 1996, at 1815 central standard time, a Cessna 182P, N9901M, was substantially damaged during a forced landing near New Orleans, Louisiana. The private pilot and his passenger were not injured. The aircraft was being operated by the owner, under Title 14 CFR Part 91. The flight originated from West Houston Airport near Houston, Texas, at 1545. Visual meteorological conditions prevailed for the cross country flight and a flight plan was not filed.

The pilot reported that ATC gave him vectors for a visual approach to Lakefront Airport in New Orleans, which is located on the shore of Lake Pontchartrain. The pilot stated that the controller kept him at 3,500 feet MSL until he was handed off to the Lakefront Airport tower controller and he was 6 miles directly south of his landing runway, 36L. The pilot further stated that he told the tower controller that he "needed to spiral down to start (the) approach to 36L," which he did with carburetor heat on and a power setting of 1500 to 1700 RPM.

The pilot reported to the investigator-in-charge that while descending through the first 3,000 feet that he did not clear the engine. The pilot recounted that the RPM began "falling off." The pilot increased the throttle, but with no rise in RPM. The pilot reported that he could not make the runway, so he lined up for a street that "appeared clear and long enough for a safe landing." The pilot reported not seeing a levee wall, due to "dusky conditions and slight haze," until he was in the landing flare. The right wing of the aircraft impacted the wall along the right side of the road, turned the airplane clockwise 90 degrees, and slid along the ground beside the wall until coming to rest.

According to the National Weather Service, located at Lakefront Airport, the temperature on the ground at the time of the accident was 44 degrees, dew point was 16 degrees, and the relative humidity was 22 percent. A second National Weather Service facility is located 13 nautical miles north east of Lakefront at Slidell, Louisiana, and 1 hour and 10 minutes before the accident, they launched a weather balloon. The data that they collected indicated that there was a temperature inversion with an accompanying steady increase of humidity of 22% on the ground to 49% humidity at 5,000 feet(see enclosed data).

A review of the literature on carburetor icing indicates the unpredictable nature of this phenomenon. One source stated that carburetor ice could manifest from 20 degrees to 90 degrees with "high" humidity. Another source stated that carburetor icing could occur from 10 degrees to 100 degrees with relative humidity greater than 20 percent. Carburetor icing characteristics do vary from airplane to airplane to include the efficiency of the cooling of their carburetion system, the power setting, the phase of flight, the mixture control setting, and the shape of the induction manifold.

The U.S. Department of Transportation FAA Flight Training Handbook states in the section under "Descents (Maximum Distance Glides)" that during "power-off descents, the engine should be cleared periodically to prevent excessive cooling and fouling." The engine manufacturer, in one of their Operator's Manuals, states that "carburetor heat is available only at engine outputs well above idle." The Federal Regulations Part 3, which dictates requirements for airworthiness certification, states that an induction de-icing and anti-icing system "provide a preheater which is capable of providing a heat rise of 90 degrees Fahrenheit when the engine is operating at 75 percent of its maximum continuous power."

The engine was test run on the airframe. According to the manufacturer, who performed the test run, the engine "start up was immediate, and the engine ran smoothly."