Cessna 210 Centurion / Turbo Centurion 210C; 210D
Flight Crew Multiengine; Flight Crew Commercial; Flight Crew Instrument
Flight Crew Last 90 Days 53; Flight Crew Total 4000; Flight Crew Type 53
Time Pressure; Troubleshooting
Aircraft Equipment Problem Critical
Flight Crew Diverted; Flight Crew Overcame Equipment Problem
Aircraft
During let-down on a VFR descent from 11;000 ft.; I noticed the power would not retard below 22 inches of manifold pressure. I continued my let-down to ZZZ1 to 1000 ft. above the pattern altitude while troubleshooting the problem. I lowered the landing gear to increase drag in an attempt to get below flap extension speed. I had to apply approximately 2Gs to the aircraft to slow to flap speed. Once the flaps were extended; I determined that the aircraft would continue to accelerate; I raised the flaps.During troubleshooting; I noticed that I could still get maximum power if required. I let traffic in the ZZZ1 pattern know that I was an emergency; and that I was working the issue. A local pilot awaiting takeoff (who apparently was also an Airframe and Powerplant Mechanic; and an Inspection Authority) recommended leaning the engine to LOP (Lean of Peak) on final to control airspeed; and a diversion to ZZZ due to more runway available. This comment was helpful; as I was already considering a diversion due to greater runway length; and the availability of emergency crews. After one turn over the airport; I diverted to ZZZ.I contacted ZZZ Approach; formerly requested priority handling with them and [stated] my intentions. I was able to clear the terrain between ZZZ1 and ZZZ easily and set up for a long; flat; straight-in approach to Runway XX. The handoff to Tower was uneventful. I flew a flat; power-on approach and maintained approximately 120-130 KIAS. As I approached the runway; I gradually leaned the engine to the onset of roughness. I maintained a zero-flap approach. As the aircraft slowed; I lowered flaps to 10 degrees; and executed a normal landing. While in the flare; I reduced the mixture to idle cut-off and touched down. I maintained an aero-brake; and lowered flaps to 30 degrees to increase drag. I turned off at the taxiway turn-off; with approximately 3000 ft. remaining. Airport Fire and Rescue helped recover the aircraft to the FBO maintenance hangar.Post-flight maintenance revealed the control rod from the throttle housing to the waste gate controller had become disconnected; preventing the waste gate from fully opening; and provided boosted power with the throttle fully retarded.Kudos to the crew at ZZZ1 for offering help without knowing I am a former military pilot. Their timely comment confirmed for me an appropriate action; and helped me maintain control in a critical phase of flight.
A C210 pilot reported he could not reduce power below 22 inches of manifold pressure during descent for landing. The pilot diverted and landed safely.