LAX98LA107

The pilot reported that he had received a weather briefing which informed him of occasional IFR conditions along the route of flight and that VFR was not recommended. He then filed a VFR flight plan. The pilot reported that he was flying on top of an overcast layer about 14,500 feet msl when he noticed that the carburetor air temperature gauge needle was moving into the yellow caution zone and the engine was running a little rough. He applied carburetor heat and noted that the ambient air temperature was at 0 degrees Fahrenheit and there were water rivulets running from the underside of the wing, in clear air. He stated that he then realized that the weather conditions were conducive to clear air icing. The needle of the carburetor air temperature gauge moved back into the yellow cautionary area although the carburetor heat was full on. Subsequently, the engine quit and the pilot stated that, 'it was immediately obvious to me that the carburetor had failed because of icing.' He then made a forced landing to a mountainous area and collided with rough terrain during the landing roll.

On March 6, 1998, at 0845 hours Pacific standard time, a Cessna 182, N6799M, lost power and made a forced landing to an open field approximately 20 miles northeast of Pioche, Nevada. The aircraft sustained substantial damage; however, neither the pilot nor his passenger were injured. The personal flight originated at the Chandler, Arizona, airport at 0545, and was en route to Ely, Nevada. The pilot stated that he was able to maintain visual flight rules (VFR) throughout the flight. A VFR flight plan was filed.

The pilot reported that he obtained a weather briefing from the Prescott Flight Service Station about 0520 on the morning of the accident. At that time, he was advised that a low pressure system was moving through the area and that occasional IFR conditions could be expected along his route of flight, with some mountain obscuration and rime icing in the clouds above 7,000 feet. The pilot was also told that there would be broken and scattered layers of clouds along the route and that the visibility at Ely, Nevada, was 2 miles with anticipated snow showers in the area throughout the day; he was then informed that VFR was not recommended.

The pilot reported that he was flying on top of an overcast layer about 14,500 feet msl. He was not using supplemental oxygen, nor did he have it available. He stated that he then noticed that the carburetor air temperature gauge needle was moving into the yellow caution zone and the engine was running a little rough. The pilot reported that he then leaned the mixture and applied full carburetor heat. He then reduced the carburetor heat to try to find the right mix of temperature and mixture for the maximum engine efficiency. The needle of the carburetor air temperature gauge started going back into the yellow arc and the pilot applied full carburetor heat and left it on.

The pilot stated that at that time he noted that the ambient air temperature was at 0 degrees Fahrenheit and there were water rivulets running from the underside of the wing, in clear air. He reported that he then realized that "the super cooled moisture in the clear air was a perfect condition for clear air icing," and saw that the needle of the carburetor air temperature gauge was back in the middle of the yellow arc although the carburetor heat was full on. Subsequently, the engine quit and the pilot stated that "it was immediately obvious to me that the carburetor had failed because of icing." The pilot then made a forced landing to a mountainous area approximately 20 miles northeast of Pioche, and collided with rough terrain during the landing roll. He reported that he broke out of the clouds about 200 feet agl.

Upon recovery, the aircraft retriever reported that he found fuel in the engine fuel lines and the carburetor bowl. He drained approximately 15 gallons of fuel from each of the main tanks. He reported that the fuel was blue in color and the odor was consistent with 100LL aviation fuel. He did not observe any visible contamination.

A Safety Board investigator conducted an examination of the engine on April 6, 1998. He reported that there was mechanical continuity established from the propeller to the accessory section and valve assemblies. Thumb compression was verified in all six cylinders. There was oil present under each of the rocker covers, with no evidence of overheating or coking.

The air box was crushed, the air filter was clean and in place, and the carburetor heat valve was in the hot position.

The spark plugs showed normal color, wear patterns, and electrode gaps according to the Champion Check-a-Plug Chart. All the spark plug leads sparked in proper sequence with hand rotation of the propeller.

The carburetor bowl was clean and the venturi was in place. The metal floats were sealed and showed no signs of rubbing or chafing. The fuel inlet screen was clean and unobstructed. The butterfly valve was free from sticking or binding when rotated by hand.

The exhaust muffler was intact and unobstructed.