Narrative:

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.

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Original NASA ASRS Text

Title: 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.

Narrative: 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.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.