PA-32 pilot reported an elevator control failure during cruise flight in VMC conditions; which resulted in the inability to provide minimal pitch control inputs. The pilot contacted ATC and diverted to an alternate airport; and performed a hard landing to a safe stop.

Narrative

The weather was beautiful VFR with 6 knot winds out of the north; clear skies; and unlimited visibility. After a full day of fishing; two friends and I were on our way home and departed Runway XX at ZZZ uneventfully with a normal takeoff with one notch of flaps. The air was smooth due to a cold front that had blown through the evening before which made what is a typically warm and bumpy afternoon flight very pleasant. After climbing through 4;000 ft. I began to chat with the passenger in the right seat about his flight training experience as he had recently completed 3 flights with a local CFI as part of his initial training. He asked a question about why I was able to fly the plane 'hands off' which led to a discussion about pitch trim and the importance of learning how to properly use it to make his flight training easier. Since I am a CFI as well; I took the opportunity to provide a short demonstration on the effect of power inputs on the attitude of the aircraft when trimmed for a specific airspeed. Once established at the cruising altitude of 4;500; I then proceeded with a short demonstration of the effect of the trim wheel on the required control forces. At this point we were at a reduced power setting at approximately 100 KIAS and I began to roll in nose down trim. Shortly after dialing in some nose down trim I reached down to the trim wheel to reverse the required control pressure and; nearly simultaneously; heard an audible bang as the airplane pitched nose down in a violent manner and departed controlled flight. The force of this pushover generated negative G's as dust and dirt from the last 40+ years flew up in the air from every crack and crevice in the plane. I immediately pulled rearward on the control yoke; only to find there was no resistance in the control pressure. Simultaneously with pulling the yoke; I spun the trim wheel back for nose up trim. This; coupled with the aerodynamic effects of the increasing airspeed from the nose down pitch attitude (and possibly the negative G unloading of the control surfaces) had the effect of stabilizing the aircraft as we ended up in a near-level flight attitude at 4;000 ft. MSL. In an effort to identify the cause of the pushover; I glanced over my left shoulder to ensure the tail was intact. Once I visually confirmed there was no airframe failure; it became clear that the elevator control cable had snapped. Further compounding our bad situation; in the violence of the pushover and resulting recovery; the trim wheel had slipped past its stops resulting in almost no range of nose-up motion for the pitch trim which was extremely concerning. I had previously set up COM1 with ZZZ Approach in the active window in anticipation of our arrival at ZZZ1 so I reached out to them and [advised them of the situation]. Unfortunately; at this point we were slowly descending and still pretty far from ZZZ1 so the radio transmissions were garbled; leading to a handoff to ZZZ Center. After contacting ZZZ Center and re-declaring the emergency I informed them of our intention to head directly to ZZZ2. I briefly considered ZZZ3 due to the longer runway length and ARFF equipment on the field; but was concerned about the lack of nearly any pitch control and was concerned that any delay in getting the plane on the ground left time for another cascading failure that could have rendered the aircraft uncontrollable. I felt like we could get the airplane to ZZZ2 with minimal control inputs based on our shallow descent profile due to our proximity (approximately 12 NM away). Despite lacking ARFF on the field; I was familiar with the airport and knew the runway was long enough for a no flap landing (5;000 ft.) at our current speed of 100 KIAS and asked ZZZ Center to have the local fire department roll the trucks to meet us at the airport. After talking to ZZZ Center; I switched to the local UNICOM and made a radio call with our location; emergency status; and intent to land on Runway XY (our enroute course was 348 degrees so we were effectively on an extended base leg already). I continued to be concerned about the source of the failures of the elevator cable and the pitch trim and worried that a loose cable could get snagged in the rigging or slip off of a pulley and bind so I used gentle power inputs almost exclusively for pitch control as any further flight control malfunctions at pattern altitude or below would not have been recoverable. For this same reason I elected to leave the flaps retracted as we had no way to compensate for the resultant pitch changes from the flap extension. We flew a shallow approach with a wide; shallow turn from base leg to final and easily maintained the glide slope with a steady pitch attitude using only small power inputs. Prior to landing; I instructed both passengers to open their doors in flight as I felt that there was a good chance of porpoising and gear collapse due to our inability to flare as we were at the limit of our nose-up elevator authority. With the likelihood of a runway departure ahead of us; and the possibility for a bent airframe; I wanted to ensure the exits were open. The flat approach attitude with no flare resulted in a very firm; 3-point landing; which bounced the aircraft. It quickly settled down and bounced a couple more times; but the trim and stabilator position were sufficient to keep the nose from dropping in the bounce and the plane from porpoising or wheelbarrowing. Needless to say; there was a big relief once all 3 wheels were on the ground and stayed there. After shutting down; we opened the access panel from the baggage compartment into the tail and quickly identified the source of the failure as the turnbuckle on the elevator cable. The metal was clearly corroded all the way through and failed in the swaged metal end of the turnbuckle under the area that had been wrapped in safety wire. I believe that an AD exists for a corrosion inspection on this turnbuckle in the PA28 series aircraft (albeit on the threads; which is not where our point of failure); but not on the PA32 series. I reported the incident to the authorities the evening after the flight; but have not heard back yet. It is clear that this failure was going to occur sooner or later as it was in an area that is not visible during a normal annual inspection and there was no requirement to perform any further inspection(s) on it. As such; it seems that an AD to address this corrosion issue on the PA32 series of aircraft should be considered. We were very fortunate that this failure occurred at a comfortable altitude; on a clear VFR day; close to a familiar airport that was suitable for landing. This event would have been unrecoverable had the failure occurred on a turn from base to final or while maneuvering in the pattern.