COMMUTER LTT TAXIED INTO POS FOR AN INTXN TKOF THEN DISCOVERED THEY WERE NOT LEGAL TO START TKOF FROM THE INTXN.

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WE ACCEPTED TKOF AT Q3 ON RWY 12. WHILE IN POS AND CLRED FOR TKOF WE DISCOVERED WE COULD NOT USE Q3 INTXN FOR TKOF. WE TAXIED FORWARD ON THE RWY AND SAID WE WERE GOING TO EXIT THE RWY AT THE NEXT L; BECAUSE WE WERE NOT SURE IF WE WERE LEGAL TO DEPART FROM THAT INTXN. WHILE WE TAXIED OFF THE RWY WE NOTICED #2 ENG INSTS READINGS WERE NOT PROPER. WE REQUESTED TAXI BACK TO THE GATE AND A MECH SAW RIGHT AWAY THAT THE START LOCK ON THE #2 PROP WASN'T DISENGAGED AND SENT US ON OUR WAY. NO WRITE UP WAS MADE AND NO MAINT WAS DONE. TO PREVENT BOTH SITUATIONS FROM HAPPENING AGAIN I SHOULD MAKE SURE WHICH INTXN I CAN DEPART FROM. ALSO IF MAINT LOOKS AT THE ACFT WE SHOULD HAVE THEM SIGN THE LOGBOOK. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO. THEY HAD TO SHUT DOWN AT THE BLOCKS BUT THEN THEY DID THE COMPANY MECH IMMEDIATELY SAW THAT THE #2 PROP WAS STILL IN FLAT PITCH. HE ADVISED THEM TO LEAVE THE PROPS IN REVERSE LONGER SO THE START LOCKS WOULD HAVE TIME TO DISENGAGE. RPTR ADMITTED THEY HAD NOT CHKED THE ENG RPM AS THEY TAXIED OUT.