A Christen Eagle II left aileron ceased responding in flight so an emergency was declared and the aircraft returned to the departure airport where the pilot discovered a push rod bolt missing and a broken aileron bell crank.

Narrative

While practicing aerobatic maneuvers (after several minutes of aerobatics; not at the beginning of the flight); the airplane roll response felt abnormal for this airplane. All maneuvers had been performed within the operating limits for this airplane. I established straight and level flight; and determined that the left ailerons were not responding to control stick inputs. The right ailerons worked normally. Note this is a biplane with ailerons on both the upper and lower wings. I established a course back to the nearest airport; home base for this aircraft; and contacted the Tower to let them know I was inbound with a flight control problem. After initial radio communication with Tower; I seemed to have lost the side-tone in my headset and was unsure if my transmissions were being heard by the Tower. I elected to squawk 7600 to make it clear to the Tower that I was having some radio issues too. I could hear their transmissions; so Tower requested that I respond to their questions by pressing the IDENT button on the transponder. I confirmed in that manner that I was declaring an emergency. By this time; I had spent a few minutes slowing down to normal approach speed; while at a safe altitude; and determined that control authority was sufficient to continue safe flight and landing. I proceeded to the airport and landed without any further problems. Post-flight inspection of the aircraft found bolt which secures the control push rod to the bell crank to be missing; and part of the bell crank had broken off. New parts will be installed; and corresponding parts on the right side ailerons have been inspected to make sure they are in good condition. My pre-flight inspection had included a check on these bolts; and the felt secure to my fingers at that time. Several weeks prior to this incident; I had found this bolt to be loose; and did not fly the airplane that day. It was tightened by one of the other owners; and it safely flew a number of hours after this fix; without incident. The radio will also be checked prior to return-to-flight status. I did confirm that my headset is working properly by testing it in another aircraft.