Accident Overview
On April 1, 2020, at about 1310 central daylight time, a Beech M35 airplane, registration N9883R, sustained substantial damage during an accident near Sequin, Texas. The pilot and passenger were not injured. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as a personal flight.
Pilot's Account of the Flight
According to the pilot, during the initial climb, the No. 3 cylinder exhibited a cylinder head temperature (CHT) approximately 60° cooler than the other five cylinders. At 1,000 ft above ground level, the pilot made the first power reduction from takeoff power to 2,500 rpm and 25 inches of manifold pressure. A normal reduction in fuel flow was performed with the mixture control. Immediately thereafter, the pilot heard and felt a loud, continuous rhythmic banging noise. The No. 3 cylinder CHT had dropped to 220°F; however, all other engine instruments remained within normal ranges, and the engine continued producing power.
Decision to Return and Landing
The pilot decided to return to the departure airport. He assessed that if a total loss of engine power occurred, sufficient altitude and airspeed existed to turn base and final for a landing on the departure runway. He planned a touchdown point on the grass runway beyond the normal touchdown point.
On final approach for runway 14, the pilot concluded the airplane was "high and fast" and lacked sufficient altitude to perform descending turns. He stated he was committed to the landing despite knowing he would land "long and hot." After touchdown on the dry grass, the rollout was described as "completely under control" but with a high groundspeed. The airplane crossed the end of the runway and traveled past the overrun area, impacting a small metal farm fence and coming to rest upright.
Damage and Postaccident Findings
The outboard portion of the right wing struck a small tree trunk, rotating the airplane 180° back toward the runway, causing substantial damage. The pilot reported that the engine continued to run until he shut it down. The pilot and passenger egressed without further incident.
Engine and Fuel Examination
The pilot reported departing with 52 gallons of fuel; all four fuel tanks contained fuel, and no leaks were present after the accident. A postaccident engine examination revealed a small amount of unidentified debris under the fuel manifold valve screen. No other preimpact anomalies were noted. The airframe was released to salvage before a detailed examination could be completed.
Additional Information
The No. 3 cylinder is located on the right side of the engine, between the No. 5 (forward) and No. 1 (aft) cylinders. The FAA-approved Continental Motors Operator’s Manual for the IO-470 series engine notes that cylinder cooling depends on proper baffle fit and operational practices, including power settings and mixture control. The FAA Airplane Flying Handbook lists three probable causes for low CHT: excessive cowl flap opening, excessively rich mixture, and extended glides without clearing the engine; corrective actions include adjusting cowl flaps, mixture control, and clearing the engine.