The pilot of the Cessna Conquest reported that during the
take-off roll, the aircraft started to rotate of its own accord at
70 knots indicated airspeed.
With what he thought to be full forward trim selected and full
forward pressure on the control yoke, the aircraft continued to
climb. The pitch attitude increased further as the landing gear and
flaps were retracted. Approaching 4,000 ft, the pilot reduced power
and was able to maintain level flight. After checking the aircraft
controllability in the approach and landing configurations, the
pilot returned the aircraft to the departure airfield for an
uneventful, although overweight, landing.
The subsequent maintenance investigation found the spiral groove
in the trim wheel that drove the trim indicator needle had a piece
broken out of it. This caused the trim needle to stick in the
take-off position. Maintenance personnel reported that the pilot
later stated that during the climb he had attempted to trim in
order to compensate for the pitch up. While doing so he felt a
resistance in the trim wheel and assumed that the trim system had
failed. Therefore he stopped trying to operate it. The pin was
stuck in the damaged groove section and had increased the force
required to move the trim wheel. Had the pilot applied additional
pressure to the trim wheel, he would have overcome the restriction
and regained trim authority. However, as he was not aware of the
cause of the increased resistance in the trim system, he elected
not to do so in case this action aggravated the situation.
A major defect report was submitted to CASA.