Chancellor 414A / C414
Flight Crew Commercial; Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 50; Flight Crew Total 3500; Flight Crew Type 1200
Confusion
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Maintenance; Inflight Event / Encounter Loss Of Aircraft Control
Flight Crew Landed in Emergency Condition; General Declared Emergency; General Maintenance Action
Incorrect / Not Installed / Unavailable Part; Human Factors; Aircraft
After an uneventful flight to verify that the Right engine was running properly after an [Engine] Top Overhaul; we descended from 9;000 feet trough a thin cloud layer and were vectored on to a 7-mile visual approach on 27L at ZZZ. Conditions at the time at ZZZ (from memory) Temp -7C; Wind 240 12G20; Bar 30.18.   Upon reaching 3000 feet and a 5-mile final; I held the nose up slightly to bleed off some extra airspeed in order to get the airplane within the gear extension speed of 139kts.  At 3000 feet and approximately 145kts; the airplane pitched down violently; suddenly; and without any change in control input on my part. I had a Mechanic-Passenger with me in the right front seat; and it took both of our strength to pull out of the dive; which was accomplished at approximately 2000 feet.  Once the nose was raised; the airspeed began to bleed off below 130 kts; and the back pressure required to maintain the correct pitch profile for the approach was less.  As the speed lessened; the pitch force was easier; but still took some strength on my part to hold the correct attitude ... We landed uneventfully. Soon after the initial 'dive' out of 3000 feet; I declared an emergency; thinking we may not be able to control the airplane; may have a hard landing; and/or may need to land gear up (the lowering of the landing gear initially added to the pitch down moment). With airspeed below 110 kts; I again extended the landing gear; and it was possible to control attitude; and at landing; around 80-90kts; I could more easily control pitch; although it still took a moderate amount of backpressure.  Upon inspection of the Trim System; it became apparent that the trim cable had broken and/or became fowled by the fact that the trim wheel would only turn in one direction; and made a grinding noise.  Upon further inspection; the turning of the trim wheel had no effect in moving the trim tab on the Right Horizontal Elevator.  This tab seemed to be stuck fully in the trim 'Down' position.  Reason for this malfunction is not yet understood; and the above inspection was done by a non-Mechanic Pilot.  ZZZ Flight Service (Mechanic) [filed] a full report.
Reporter stated the Cessna C-414 and C-421B aircraft have only one Elevator Trim Tab located on the Right Elevator inboard trailing edge. The C-414 Elevator Trim Tab actuating rod end attaches to the tab with a bolt and nut arrangement; both of which were found missing after he landed. The nut does require a cotter key for safety. No indication on the rod end; or on the tab; that excessive force had sheared the bolt and allowed the rod to separate. Suspicion is the cotter key was partially installed; or not installed at all. An Annual Inspection had just been completed on the aircraft.  Reporter stated the actuating rod end connection to the tab is visible under the elevator and not covered by a fairing.  Normally the tab would go to a neutral position if the rod end disconnected from the tab. But in their incident; the rod end had actually popped-up; out of the attach fitting on the tab and jammed into a concaved area of the tab leading edge. That action jammed the tab trailing edge down and a pitch down condition for the airplane. He could not believe how much back pressure and effort was required of himself and the Mechanic; who was performing a Maintenance Check ride along; to get the nose back to level flight. At one point; they did not feel they would get control of the aircraft. Reporter stated the aircraft has had a rough life; since the entire Tail Assembly (Horizontal; Rudder; Elevators) have been removed twice due to mistakes made by the Repair Facility during maintenance. Once; when after a jacking pole supporting the Nose Gear collapsed and drove the Tail section into the Hangar ceiling structure. The second time; when the engines had been removed to upgrade the Powerplants to a RAM System and Avionics techs walked to the back of the aircraft and the Tail section slammed down on the concrete flooring. He suspects; that when the Tail section was reassembled the second time; the cotter pin was not installed at the tab rod end.
Cessna 414 pilot describes his efforts to regain aircraft control after a violent and sudden pitch down; without any change in his control input. Full back pressure efforts by himself and a ride-along Mechanic were required to pull the aircraft out of the dive. Subsequent inspection revealed; the Right Elevator Trim Tab actuating rod had separated from the tab and jammed the tab in a nose down condition.