LAX03LA235

The engine lost power during cruise flight, and the helicopter collided with high vegetation during an autorotative descent. Just before touchdown during the forced landing, engine power was restored; however, the pilot decided to concentrate on successfully completing the forced landing. The helicopter touched down in high vegetation and was substantially damaged. The power loss was not preceded by any auditory or visual warnings, and none occurred during the descent. Following recovery of the helicopter from the remote site, the engine was visually examined then placed into a test cell and run up. During the first engine run, the engine exhibited the following results: (1) normal start; (2) normal warm-up; (3) lean operation upon accelerating between 2,250 and 2,300 rpm with no fuel boost pump on; (4) upon turning on the test cell's fuel boost pump, the engine accelerated between 2,700 and 2,800 rpm with no hesitation. During the second engine run, with a carburetor from another Lycoming O-540 engine, the accident engine operated normally during run up to full power without the test cell's fuel boost pump turned on. Thereafter, the accident carburetor was examined, including a flow bench test, and no abnormalities were found that would have prevented the carburetor from functioning within prescribed design specifications. The reason for the excessively lean mixture/restricted fuel flow, which reduced the engine's available power, was not ascertained.

On July 17, 2003, about 1305 mountain standard time, a Robinson R44, N8329B, experienced a total loss of engine power while cruising about 12 miles northeast of Happy Jack, Arizona. The private pilot performed an autorotative descent into the underlying rough terrain. During the descent, just before touchdown, the pilot was able to restart the engine. The pilot reported that, at the time of the restart, he needed to concentrate on performing the forced landing to avoid rolling down the underlying hill. During the landing sequence, the helicopter collided with high vegetation and was substantially damaged. Neither the private pilot nor the passenger was injured. Visual meteorological conditions prevailed at the time of the personal flight, and no flight plan was filed. The helicopter was owned and operated by the pilot. The flight was performed under the provisions of 14 CFR Part 91, and it originated from Flagstaff, Arizona, about 1245.

The pilot subsequently reported to the National Transportation Safety Board investigator that during the cruise flight the engine suddenly lost all power while cruising about 6,000 feet mean sea level. The power loss was not preceded by any auditory or visual warnings, and none occurred during the descent. The pilot stated that after the engine lost power he only concentrated on the autorotation.

The helicopter wreckage was airlifted out of the remote accident site and was examined by the Federal Aviation Administration (FAA) coordinator. The helicopter's engine was placed into a test cell. The FAA reported that during the first engine run the engine exhibited the following results: (1) normal start; (2) normal warm-up; (3) lean operation upon accelerating between 2,250 and 2,300 rpm with no fuel boost pump on; (4) upon turning on the test cell's fuel boost pump, the engine accelerated between 2,700 and 2,800 rpm with no hesitation. The FAA additionally reported that during the second engine run, with a carburetor from another Lycoming O-540 engine, the accident engine operated normally during runup to full power without the test cell's fuel boost pump turned on.

The accident Precision Airmotive Corporation carburetor, Model MA-4-5, part number 10-6035-11, serial number 75079404, was sent to its manufacturer for examination under the supervision of a Safety Board investigator. The examination, including a flow test, did not reveal any abnormalities that inhibited the carburetor from functioning within prescribed design specifications. The reason for the excessively lean mixture/restricted fuel flow, which reduced the engine's available power, was not ascertained.