American AA-1 N623W

The pilot reported that after starting the engine he obtained the current weather conditions and then requested taxi clearance from ground control for the 10-minute flight. After takeoff, while about 500 ft above ground level (agl), the engine momentarily reduced to about 800 rpm and then abruptly returned to full power. The pilot began to turn back toward the airport and contacted the airport control tower and advised that the airplane lost power, but it had come back and he needed to get on the ground. The tower controller provided instructions to return and asked the pilot to restate the problem. The pilot advised that the airplane lost full engine power, and it was “cutting in and out.” The engine then reduced to idle before “quitting entirely.” The pilot attempted to troubleshoot the issue by using the fuel pump, switching fuel tanks, and checking the mixture. He did not report if or how he applied carburetor heat. He determined the airplane would not reach the runway and selected a nearby road for a forced landing. During the approach to the road, the airplane impacted a wire before it came to rest in the grass median. The pilot stated that he performed the engine runup and his instrument checks while “on the taxi down to runway 27.” The amount of time the engine was running while on the ground could not be determined; however, the summary of Federal Aviation Administration (FAA) air traffic control communications indicated that about 3 minutes elapsed between the request for taxi and the clearance for takeoff. The weather conditions reported at the departure airport near the time of the accident included a temperature of 14°C and a dew point 7°C, with a calculated relative humidity of 63%. These conditions were conducive to serious carburetor icing at cruise power settings. The likelihood and severity of carburetor icing is increased at the lower power settings that would have been used while on the ground. The pilot did not report if or how he applied carburetor heat during the ground operations. Typically, in general aviation operations, the before-takeoff checklist is completed in a run-up area or near the hold-short line before the airplane takes the runway for takeoff. In this case, the pilot apparently performed the before-takeoff checklist while taxiing for takeoff. During the engine run-up, he might have overlooked performing the carburetor heat check, or he performed the check so quickly that it did not have any practical effect on ice building up in the carburetor. Although a check of its operation is part of the engine run-up checklist, had the carburetor accumulated a significant amount of ice that check may not have been sufficiently long enough to completely melt it. During the postaccident examination of the airplane, it was noted that one of the four leads of the right magneto did not spark when the drive coupling was rotated. It is likely that the anomaly was due to impact forces; if not, the faulty condition would have been detected during the magneto check during the engine run-up. Additionally, a faulty lead on one magneto would not have resulted in a complete loss of engine power as reported by the pilot. Otherwise, the postaccident examination of the airplane did not reveal any mechanical anomalies that would have precluded normal engine operation. Given the weather conditions that were conducive to serious carburetor icing at cruise power, the pilot’s reporting of a loss of engine rpm and the subsequent “cutting in and out” of the engine, the loss of engine power was likely due to the accumulation of carburetor ice.

Quoted verbatim from the NTSB record.