WPR21LA141

During a night instrument flight rules cross-country flight, the airplane encountered weather that included clouds and icing conditions. Shortly thereafter, the engine began to run rough and lose power; radar contact was lost, and the airplane was located in mountainous terrain. Postaccident examination of the airframe and engine revealed no mechanical anomalies that would have precluded normal operation. Weather conditions reported at the time of the accident were conducive to the formation of serious carburetor icing at cruise power settings. The pilot reported that, during a climb into clouds, with the carburetor heat off, the engine began to run rough and was losing rpms before he applied carburetor heat. Therefore, it is likely that carburetor ice accumulated during the climb, which resulted in a partial loss of engine power.

HISTORY OF FLIGHT On March 24, 2021, 0021 mountain daylight time, a Mooney M20B, N74786, was substantially damaged when it was involved in an accident near Animas, New Mexico. The pilot and passenger were seriously injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that, while on an instrument flight rules (IFR) flight plan from Fort Stockton-Pecos County Airport (FST), Fort Stockton, Texas, to Tucson International Airport (TUS), Tucson, Arizona, the airplane was accumulating light rime ice at 8,000 ft mean sea level (msl). He contacted Albuquerque Air Route Traffic Control and was instructed to climb to 14,000 ft msl. During the climb to 14,000 ft, the pilot reported climbing into clouds; the engine began to run rough and lost partial power. He applied carburetor heat and checked both magnetos. The pilot believed that he had lost both magnetos. The airplane became the subject of an alert notice (ALNOT) after radio communication and radar contact was lost. According to responding law enforcement, the airplane came to rest in mountainous terrain at an elevation about 5,010 ft msl about one mile northwest of Pinkey Wright Mountains. A postaccident examination of the airframe and engine revealed no mechanical anomalies that would have precluded normal operation. The magnetos remained secured and attached to their respective mounting pads on the engine. Both magnetos were removed and manually rotated with spark observed at each P-lead. Flight control continuity was established from the cockpit to all the flight control surfaces via their respective cables and hardware. METEOROLOGICAL INFORMATION The closest recorded aviation weather station was Grant County Airport (KSVC), Silver City, New Mexico, about 44 miles northeast of the accident site at an elevation of 5,446 ft msl. Recorded weather at 0015 included wind from 300° at 9 knots, 10 miles visibility in light rain, a broken ceiling 1,300 ft above ground level (agl), an overcast cloud layer at 2,200 ft agl, temperature 35° F, dew point 33°F, altimeter 29.79 inches of mercury (inHg). AIRMET advisories for mountain obscuration conditions, moderate turbulence below 16,000 ft, and moderate icing between the freezing level and 20,000 ft msl were valid for the area of the accident site at the time of the accident. The atmospheric sounding supported an overcast layer of clouds with bases near 200 ft agl and tops to 16,000 ft msl, rain showers, and a freezing level of 1,400 ft agl (6,400 ft msl). The sounding also supported the potential for light to moderate turbulence between 5,800 and 17,000 ft. Light rime to clear type icing in the clouds was identified between 6,400 ft and 16,000 ft. The Federal Aviation Administration Special Airworthiness Information Bulletin CE-09-35, Carburetor Icing Prevention, stated the following: Pilots should be aware that carburetor icing doesn't just occur in freezing conditions, it can occur attemperatures well above freezing temperatures when there is visible moisture or high humidity. Icing can occur in the carburetor at temperatures above freezing because vaporization of fuel, combined with the expansion of air as it flows through the carburetor, (Venturi Effect) causes sudden cooling, sometimes by a significant amount within a fraction of a second. Carburetor ice can be detected by a drop in rpm in fixed pitch propeller airplanes and a drop in manifold pressure in constant speed propeller airplanes. In both types, usually there will be a roughness in engine operation. The special airworthiness information bulletin included a chart that showed the probability of carburetor icing for various temperature and relative humidity conditions. According to that chart, the weather conditions at the time of the accident were conducive to serious carburetor icing at cruise power.