Narrative:

During the takeoff and initial climb of an IFR training flight; the aircraft began [an] uncommanded pitch up and pitch down movements; then began pitching up.the instrument student attempted to control this by using the electric trim controls on the left side of the control yoke and was unsuccessful. Several seconds later; the red 'pitch trim fail' indicator light illuminated and the aural beep commenced. The aircraft began another uncommanded pitch up; at which point the instructor took control of the aircraft; reduced thrust substantially; regained level flight; and cycled the master switch on and off to attempt to either re-set or disable the electric pitch trim. After that; the electric pitch trim became inoperative. Manual trim inputs were effected to stabilize the aircraft.the instructor requested priority handling with approach; and requested clearance to return and land at ZZZ; which was then-slightly behind the aircraft.aircraft control was regained and the electric pitch trim was inoperative; but because of the aforementioned runaway trim; the manual pitch was positioned for a nose-high attitude and was difficult to manipulate. Thrust inputs and flaps were primarily used to stabilize the aircraft's descent with minimal trim inputs for fear of setting off further un-commanded pitch trim changes.the instructor was able to land the aircraft on runway xx at ZZZ; without incident or requiring any assistance. The aircraft was taxied to the ramp and parked.

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Original NASA ASRS Text

Title: PA28 instructor pilot with a student (pilot flying) reported experiencing uncommanded pitch up and down movements during takeoff followed by a pitch trim fail indication resulting in a return to departure airport.

Narrative: During the takeoff and initial climb of an IFR Training Flight; the aircraft began [an] uncommanded pitch up and pitch down movements; then began pitching up.The instrument student attempted to control this by using the electric trim controls on the left side of the control yoke and was unsuccessful. Several seconds later; the red 'pitch trim fail' indicator light illuminated and the aural beep commenced. The aircraft began another uncommanded pitch up; at which point the instructor took control of the aircraft; reduced thrust substantially; regained level flight; and cycled the Master Switch on and off to attempt to either re-set or disable the electric pitch trim. After that; the electric pitch trim became inoperative. Manual trim inputs were effected to stabilize the aircraft.The instructor requested priority handling with Approach; and requested clearance to return and land at ZZZ; which was then-slightly behind the aircraft.Aircraft control was regained and the electric pitch trim was inoperative; but because of the aforementioned runaway trim; the manual pitch was positioned for a nose-high attitude and was difficult to manipulate. Thrust inputs and flaps were primarily used to stabilize the aircraft's descent with minimal trim inputs for fear of setting off further un-commanded pitch trim changes.The instructor was able to land the aircraft on Runway XX at ZZZ; without incident or requiring any assistance. The aircraft was taxied to the ramp and parked.

Data retrieved from NASA's ASRS site 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.