AN ATR 42 ON TKOF AT 200 FT ADVISED ATC ACFT WAS RETURNING TO THE FIELD DUE TO #2 ENG HAD AN UNCOMMANDED OVERTORQUE EXCEEDING THE ENG LIMITS CAUSED BY INTERMITTENT TORQUE SENSORS.

Narrative

IMMEDIATELY AFTER TKOF; THE #2 ENG HAD AN UNCOMMANDED OVERTORQUE WHICH EXCEEDED THE ENG LIMITATION. THE PWR WAS BROUGHT BACK TO IDLE. THE CHKLIST CALLED FOR AN ATTEMPT TO BRING THE PWR BACK UP WHICH CAUSED MORE PWR SURGES AND WINDMILLING OF THE R PROP AND EXCESSIVE YAW; SO THE ENG WAS FEATHERED. ATC WAS NOTIFIED AND AT THE TIME; THE FEATHERED ENG WAS ACTING WITHIN LIMITATIONS; SO WE DECIDED NOT TO SHUT IT DOWN FOR 2 REASONS: 1) NOT KNOWING WHAT CAUSED THE MALFUNCTION; IT WAS BETTER TO KEEP THE ENG RUNNING IN FEATHER IN CASE WE HAD A PROB WITH THE #1 ENG. 2) PAX ARE MUCH MORE AGITATED AT THE SIGHT OF A STOPPED PROP. WHEN WE CONTACTED ATC AS TO THE NATURE OF OUR PROB; THE SIT WAS UNDER CTL AND THE ACFT WAS FLYING NORMALLY; SO WE DECIDED AGAINST DECLARING AN EMER. WE RECEIVED PRIORITY HANDLING FROM EWR TWR AND WERE VECTORED FOR A DOWNWIND FOR RWY 22R. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE ENG WAS A PWC PW121A ENG AND THE FEEDBACK FROM MAINT WAS DIRTY SENSORS. THE RPTR SAID THE SENSORS WERE NOT IDENTED AS TO FUNCTION AND NOMENCLATURE.