Accident Details
On December 17, 2023, at about 1414 central standard time, a Beech B36TC, registration N70SL, was destroyed in an accident near Burnet, Texas. The pilot and passenger received serious injuries. The airplane was operated under Title 14 Code of Federal Regulations as a Part 91 personal flight.
The pilot stated that the preflight, engine start, engine runup, and takeoff roll were normal. While climbing through 200 to 300 ft agl, the engine began to surge and lose power. The airplane was unable to climb, and the pilot was unsuccessful using emergency procedures to regain engine power. The pilot reported that he could not see an area suitable to land on except for a road. During the landing, the airplane’s right wing struck a car and exploded into flames. The airplane landed in a field and was destroyed by impact forces and postcrash fire.
Witness Observations
A witness reported seeing the airplane intermittently emitting black smoke from the exhaust as it climbed out slowly after takeoff. A video of the takeoff showed dark smoke emitting from the airplane’s exhaust area. A second witness observed the airplane flying southbound at an estimated altitude of 100 to 150 ft agl and having difficulty gaining altitude. The airplane’s landing gear was retracted, the wing flaps were retracted, and the propeller was turning. The airplane lost altitude and descended behind a hill.
Investigation Findings
The engine-driven fuel pump assembly was removed for testing at Continental Aerospace Technologies in Mobile, Alabama, under the supervision of the NTSB Investigator-in-Charge. During testing at an input speed of 2,700 rpm, the fuel flow was measured at 38.42 gallons per hour, exceeding the maximum limit of 34.9 gallons per hour. No test fluid leakage was observed. The fuel pump assembly was disassembled to determine the length of its internal aneroid. The aneroid adjustment screw was extended outward 0.4480 inch. The internal aneroid was not elongated and was of comparable length to a new production fuel pump assembly, indicating a normal condition. According to Continental Aerospace Technologies, greater outward extension of the aneroid adjustment screw results in higher fuel flow output.
A review of engine maintenance logbooks showed that the fuel pump was overhauled in June 2004, and the engine was overhauled on April 14, 2022. No other references to work or adjustments on the fuel pump were found.
The Federal Aviation Administration Aviation Maintenance Technician Handbook–Powerplant (2023), Chapter 10, Engine Maintenance & Operation, Engine Troubleshooting, Figure 10-52, lists black exhaust smoke and sluggish engine operation as symptoms of a rich mixture.