Accident Summary
On March 18, 2014, about 1020 central daylight time, a Beech P35 Bonanza, registration N5932Y, sustained substantial damage during a forced landing at Kickapoo Downtown Airport (CWC), Wichita Falls, Texas. The aircraft was operated as an instructional flight under 14 CFR Part 91. The pilot sustained minor injuries; the instructor pilot was uninjured. Visual meteorological conditions prevailed, and no flight plan was filed. The flight had departed CWC around 0930.
The pilot reported turning from downwind to base leg in preparation for a short-field landing on runway 17 (4,450 feet by 75 feet, asphalt). After reducing throttle during the turn, the engine did not respond when throttle was reapplied. At approximately 600 feet above ground level, the pilot executed a forced landing to a field with mesquite bushes. The airplane sustained leading edge damage to both wings during landing.
Examination and Testing
On-site examination by FAA inspectors found 50 gallons of fuel on board and no visible engine damage. The aircraft was moved to a storage facility for further inspection. The Beech P35, serial number D-7017, was manufactured in 1962 and powered by a 260-horsepower Continental IO-470-LCN engine built in 1981. The last annual inspection was on January 1, 2014, with 5,896 total aircraft hours; the engine had 4,210 total hours and 326 hours since major overhaul. The airplane had flown 21 hours since the annual.
On May 28, 2014, an engine run was conducted with the bent propeller replaced. A 5-gallon fuel container was connected to the left fuel selector. After warm-up, the throttle was advanced to 1,700 rpm for a magneto check (75 rpm drop per magneto). When throttle was increased above 2,000 rpm at full rich mixture, the engine began losing power. An attempt to shut down using the cockpit mixture control failed because the control was stuck in the full rich position. The actuating arm on the fuel metering unit had moved over center and had to be manually returned to lean. The rich mixture stop pin on the fuel metering unit was missing, allowing the actuating arm to travel past the full rich position and over center.
A second engine run was performed with the cockpit mixture control pulled out about one inch. The engine then achieved 2,700 rpm (full power) and was shut down normally. The fuel metering unit was removed and examined; the rich mixture stop pin was missing and not located. The lean mixture stop pin was loose and removable by hand. Wear was noted on the inside of the fuel mixture actuating arm and the mixture stop on the rotating shaft. The fuel screen was clean. The unit was sent to Continental Motors, Inc. for testing.
Testing at Continental Motors
On September 9, 2014, the fuel metering unit was reassembled, examined, and flow tested. The rich mixture stop pin was missing with wear signatures in its socket. The unit functioned properly through its full range during the production test, though some leakage occurred. When the mixture control was extended past the stop pin limits in half-pin-diameter increments, fuel flow decreased: from 124.9 to 113.4 pounds per hour (pph) at the first extension, and from 133.9 to 88.9 pph at the next. The amount of over-extension from the aircraft's mixture control cable was unknown. The test demonstrated that extension past the rich mixture stop pin reduced fuel flow to the engine, consistent with the power loss experienced during the accident.