Tuesday, November 20, 2012

Carburetor icing

“The Engine Stopped Running”

A C182 Pilot learned that severe carburetor ice can form even though no airframe icing is seen. The Pilot was lucky to break out of the clouds and restart the engine.
 We were at 12,000 feet on an instrument flight plan in communication with Approach. The Controller directed us to descend and maintain 9,000 feet. Flight conditions were IMC, -4 degrees C, and no airframe icing was being encountered. We reduced throttle in order to descend and within a few seconds of reducing throttle, the engine stopped running. After completing the Engine Failure Checklist, with no success, we declared an emergency with Approach…. We continued on our present heading with the intent of making an emergency landing at a nearby CTAF airport…. Upon further discussion with the Controller, however, we elected to head for a nearby Class D airport…. As we descended (still in IMC) we were able to restart the engine…. We continued to descend towards the airport and broke out of the clouds into VMC at approximately 4,800 feet….

It is clear that this engine failure incident was caused by severe carburetor ice— just below the freezing level, in clouds, with visible ice crystals. Although the ice crystals were not of the type that created airframe ice (no airframe ice was reported in our area), it was ideal for causing carburetor ice, which built up more rapidly than we were able to clear using carburetor heat.
An NTSB report recounts how another C182 Pilot experienced carburetor icing, but was unable to restart the engine and wound up losing his airplane in a tree.
The pilot received a weather briefing from FSS the evening before departure and a friend at the destination told him that the area had been free of fog for the last several days. Upon descent to 1,500 feet at the destination, he could not spot the airport due to a fog layer. He decided to divert to his alternate. After turning toward the alternate airport, the engine began to run roughly. The pilot was unable to remedy the power loss by applying carburetor heat, switching fuel tanks, leaning the mixture, and checking the magnetos in the both position. As he turned back toward his original destination airport, the engine continued to run rough and he was unable to arrest the airplane’s descent. He was just above the fog layer, saw the runway through the fog, and turned back to the runway. During the turn, he went into the fog and the airplane collided with treetops and lodged in branches. The occupants noticed fire in the floorboard area, exited through the pilot’s door, and jumped to the ground. The fuselage was consumed by fire….

The NTSB determines the probable cause(s) of this accident to be: A loss of engine power due to carburetor icing and the pilot’s failure to use carburetor heat in conditions conducive to icing.
For details  Safety Callback 394 November 2012

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