Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor
Flight Crew Last 90 Days 50; Flight Crew Total 10000; Flight Crew Type 2000
Workload; Situational Awareness
Aircraft Equipment Problem Critical; Ground Event / Encounter Other / Unknown; Ground Excursion Runway
Air Traffic Control Provided Assistance; Flight Crew Landed in Emergency Condition; Flight Crew Took Evasive Action; Flight Crew Requested ATC Assistance / Clarification
Aircraft
We departed ZZZ on a part 91 day VFR local pleasure flight with one adult passenger in this 1979 Cessna 172N aircraft flying approximately east south east. The weather appeared to be six plus miles visibility with some cirrus clouds; winds under 10 kts. with what seemed to be an occasional thermal. Approximately ten to fifteen minutes into the flight; was at about 1;800 ft. and began a gradual turn to the right.As the yoke was first being moved clockwise; or perhaps shortly thereafter; a pop was felt; the yoke then had no resistance whatsoever with the control yoke ending up being all but fully deflected to the right where it remained at that moment. A vibration in the airframe began. It was a light though consistent somewhat disconcerting vibration. Even with the yoke as it was (all but fully clockwise at that time; in other words; the yoke was about 90 degrees clockwise from level) the aircraft was not banking right. The left rudder pedal may have been instinctively depressed to pick up the right wing after the snap occurred; but uncertain. The aircraft now appeared to not be entirely controllable as the yoke and inputs to it did not seem to be having the effect which they should have.Thereafter; if the yoke was moved counterclockwise; especially if moved past neutral to the left; a distinct buffet of unknown nature was felt; and the yoke was immediately returned to the position which resulted in the least vibration; about ninety degrees clockwise. Not being a mechanic there was significant uncertainty as to what actually was broken and what effect it could have on the flight characteristics of the aircraft. When a shallow climb was introduced or the pitch was increased; a distinct buffet of unknown nature was felt and the climb with the associated pitch and power increase was immediately discontinued and not attempted again. When a very shallow descent was introduced the ongoing vibration seemed to decrease or cease. When the engine rpm was decreased slightly the ongoing vibration also seemed to decrease. That said; no further attempts were made to bank or turn left or climb or increase the pitch or power. All turns thereafter; which were slight with little bank; to the right; were accomplished with slight rudder pressure.7700 was squawked and ATC was advised on guard. Center responded promptly to the call. Due to the limited and questionable control problem; along with the ongoing vibration and buffeting issues; the best course of action at the time appeared to be not to continue the flight back to the closest and seemingly most prudent airport as it would have required a flight directly over a densely populated area. The next closest airport considered potentially usable in the situation appeared to be ZZZ1. However; ZZZ1 was much further than ZZZ (about 18 NM vs. about 10 NM); although few homes along the route it required a flight over water which would have necessitated a climb and a left turn. Due to the buffet experienced during the prior attempted climb; local knowledge of many times there being turbulence where the water meets the land; the distance (would something else happen during that longer travel time?) and the buffet experienced when a left turn was attempted previously; ZZZ1 did not seem to be a good choice at that time.There was an acceptable looking farmer's field which required a slight turn to the right and was just prior to the populated area of ZZZ2 and ZZZ2; it seemed to be the best choice. The aircraft was maneuvered slightly right using slight rudder pressure. After the turn was completed a gradual descent at reduced power was begun. Communication with Center was lost due to the descent although an airliner relayed our communications with Center.During the descent at reduced airspeed a very minimal amount of flaps were introduced to see if any negative effect was experienced. No negative effect was experienced. The descent continued; doors were propped opened; fuel was turned off;mixture to idle cutoff; mags and master switch off which all then culminated in an uneventful though spirited landing on a farmer's field. The airplane came to rest seemingly undamaged. Aircraft was exited normally and moments later Center called to my cell phone in order to check status and get information. FSDO's and local law enforcement were notified and responded accordingly.
C172 pilot reported a complete loss of aileron control that resulted in a forced landing.