Decathlon 8KCAB
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Commercial
Flight Crew Last 90 Days 20; Flight Crew Total 580; Flight Crew Type 260
Aircraft Equipment Problem Critical
Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Departure Airport
Aircraft
On climb out approximately 7-8 miles southwest of the field; I noticed propeller RPM was less than commanded/nominal for the phase of flight. RPM should have been 2700 RPM and was indicating less than 2550 initially. Requested direct routing back to ZZZ. As a descending turn was started further non-commanded reduction in propeller rpm was observed. Attempting to maintain level flight and airspeed I observed audible and indicated abnormal fluctuations in propeller RPM. With minor changes in manifold pressure came RPM fluctuations past redline and as low as 2100 RPM without a change in commanded propeller RPM. At this time ATC asked souls and fuel on board and I was able to land without incident. ATC was very accommodating.
Super Decathlon pilot reported returning to departure airport after experiencing engine malfunction.