On November 20, 1997, approximately 1145 mountain standard time, a Cessna 150M, N714MN, was substantially damaged during a forced landing near Tajique, New Mexico. The private pilot, the sole occupant in the airplane, was not injured. The airplane was being operated by the pilot under Title 14 CFR Part 91. Visual meteorological conditions prevailed for the night cross-country flight which originated at Roswell, New Mexico, approximately 90 minutes before the accident. No flight plan had been filed.

According to the pilot, in an interview with the Investigator-In-Charge (IIC), he "preflighted the airplane and topped it off with fuel" at the Double Eagle II Airport near Albuquerque at about 2100. He stated that he immediately departed "to build time flying in the local area." He flew to Roswell, New Mexico, where he added 6 more gallons of fuel and departed for the return trip to Albuquerque. While flying over the Manzano mountains, "the engine began to sputter." He reported that he applied full carburetor heat and turned back towards a "small lighted town in the hopes of finding a field or road to land on."

The pilot reported to the IIC that, while on final approach to a field, "he hit a transmission wire with his left wing, which darkened most of the town." He landed the airplane, but during the landing roll hit a fence and a woodpile which subsequently crushed the nose wheel landing gear aft. The pilot stated that the left wing and the left stabilizer were "dented in."

The pilot stated that he had obtained weather briefings at the beginning of both legs of his trip. He further stated that he had encountered scattered clouds at approximately 9,000 feet msl during his flight to Roswell. After landing at Tajique, he reported that the surface temperature was between 35 degrees F. and 38 degrees F.

A review of the literature on carburetor icing indicates the unpredictable nature of this phenomenon. The Pilot Safety and Warning Supplements published by Cessna Aircraft Company stated that "under certain atmospheric conditions, when the relative humidity is more than 50 percent with ambient air temperatures ranging from 20 degrees to 90 degrees F., it is possible for ice to form since the temperature in a carburetor may drop as much as 60 degrees F. below the temperature of the incoming air." FAA AC 20-113 stated that "carburetor icing may occur at temperatures from 32 degrees F. to as high as 100 degrees F. with a relative humidity of 50 percent or above." Carburetor icing characteristics vary from airplane to airplane to include the efficiency of the cooling of the carburetor, power setting, phase of flight, mixture control setting, and shape of the induction manifold.

Evaluation of the weather at the time of the accident revealed a temperature between 35 degrees F. and 38 degrees F., with a dew point of 22 degrees F. The enclosed Icing Probability Chart indicates that this float type carbureted engine was being operated in a region of serious carburetor icing conditions. Furthermore, Part 3 of Airworthiness Regulations states that: "Airplanes equipped with sea level engines employing conventional venturi carburetors shall be provided with a preheater capable of providing a heat rise of 90 degrees F. when the engine is operating at 75 percent of its maximum continuous power." N714MN was flying at an altitude of 11,500 feet, and according to the performance charts, was capable of producing approximately 60 percent power.

The FAA inspectors who went to the accident site stated that the engine had "good compression, continuity checked ok, the magnetos sparked, and there was fuel in the carburetor." The engine was removed from its airframe and shipped to the manufacturer where it was functionally tested. According to the manufacturer who performed the test, the engine "start up was immediate, and the engine ran smoothly" (see attached documentation).

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