CEN14LA165

The pilot reported that, while turning from the downwind to the base leg to prepare for a short-field landing on the runway, he reduced the throttle. He then applied throttle to increase the power when the airplane was about 600 feet above ground level; however, the engine did not respond, and the pilot subsequently executed a forced landing to a field. During the landing, both wings sustained substantial damage. During an engine test run with the cockpit fuel mixture control in the full-forward position, the engine would lose power when the throttle was advanced past 2,000 rpm. When the cockpit fuel mixture control was pulled out about 1 inch, the engine would develop 2,700 rpm (full power) when the throttle was advanced. The examination of the engine revealed that the lean mixture stop pin in the fuel metering unit was loose and could be removed by hand. Wear was observed on the inside of the fuel mixture actuating arm and on the mixture stop on the rotating shaft. The fuel metering unit's rich mixture stop pin was missing, which allowed the actuating arm to travel past the full-rich mixture position. A bench test of the fuel mixture control demonstrated that extension past the rich mixture stop pin reduced the fuel flow to the engine. This condition indicates that the airplane's fuel mixture control was misrigged, which resulted in the rich mixture stop pin dislodging from the fuel metering unit. It could not be determined when the fuel mixture control was misrigged.

On March 18, 2014, about 1020 central daylight time, a Beech P35 airplane, N5932Y, sustained substantial damage after a loss of engine power while landing at the Kickapoo Downtown Airport (CWC), Wichita Falls, Texas. The pilot received minor injuries and the instructor pilot was not injured. The airplane was registered to and operated by a private individual under the provisions of the 14 Code of Federal Regulations Part 91 as an instructional flight. Visual meteorological conditions prevailed for the flight, which was not on a flight plan. The flight originated from CWC about 0930. The pilot reported that he had turned from the downwind leg to the base leg and was preparing for a short-field landing on runway 17 (4,450 feet by 75 feet, asphalt). He had reduced the throttle during the turn to base leg, but when he applied throttle to increase the power, the engine did not respond. The airplane's altitude was about 600 feet above ground level, and the pilot executed a forced landing to a field containing mesquite bushes. The airplane sustained leading edge damage to both wings during landing. The on-site examination of the airplane by Federal Aviation Administration inspectors revealed that the airplane had 50 gallons of fuel on board. No damage to the engine was observed. The airplane wreckage was transported to an aircraft storage facility for further examination and an engine run. The Beech P35 Bonanza, serial number D-7017, was manufactured in 1962. The engine was a 260-horsepower Continental IO-470-LCN, manufactured in 1981. The last annual maintenance inspection was conducted on January 1, 2014, with at total aircraft time of 5,896 hours. At the time of the accident, the engine had 4,210 total hours with 326 hours since the last major overhaul. The airplane had flown 21 hours since the annual maintenance inspection. On May 28, 2014, an engine run was conducted. The bent propeller was removed from the engine and replaced with a stock propeller. A 5 gallon fuel container was connected to the left side of the fuel selector. No other work was performed and the engine was run on the airframe. The engine was started and allowed to warm up. The throttle was then advanced to 1,700 rpm and a magneto check was performed. Each magneto had a 75 rpm drop during the magneto check. The throttle was then advanced to full throttle with the mixture full rich. When the throttle was advanced over 2,000 rpm, the engine would begin to lose power. During the first engine run, an attempt was made to shut down the engine, but the cockpit mixture control was stuck in the full rich position. The actuating arm on the fuel metering unit was over center and had to be moved by hand to the lean position. The rich mixture stop pin on the fuel metering unit was missing, allowing the mixture actuating arm to travel past the full rich mixture position and over center. The engine was run a second time with the mixture control in the cockpit pulled out about one inch. Thethrottle was advanced and the engine then ran at 2,700 rpm (full power). The engine was then shut down using the cockpit mixture control. The fuel metering unit was removed and examined. The rich mixture stop pin was missing from the fuel metering unit and could not be located. The lean mixture stop pin was loose in the fixture and could be removed by hand. Wear was observed on the inside of the fuel mixture actuating arm and on the mixture stop on the rotating shaft. The fuel screen was clean and clear. The fuel metering unit was sent to Continental Motors, Inc for further testing. On September 9, 2014, the fuel metering unit was reassembled, examined and tested at Continental Motors, Inc. The examination revealed that the rich mixture stop pin was missing and had signatures of wear in the pin socket. The fuel metering unit was flow tested and it functioned properly through its full range of operation, although some leakage was observed. Upon completion of the production test, the mixture control was extended past the stop pin limits in one-half stop pin diameter increments. The first extension reduced fuel flow from 124.9 pounds per hour (pph) to 113.4 pph. The next extension reduced flow from 133.9 to 88.9 pph. The amount of over extension the aircraft mixture control cable produced is unknown. The test demonstrated that the extension past the rich mixture stop pin reduced the fuel flow to the engine.