COMMUTER FLC TAXIES BEYOND HOLD AND ONTO RWY. IMMEDIATELY TAXIES OFF.

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CAPT WAS TAXIING ACFT; WAS TOLD TO TAXI 'A' HOLD SHORT OF RWY 2 AT PHF. MYSELF AS THE FO WAS BUSY WITH OTHER COMPANY REQUIRED DUTY CHKLISTS; PAX BRIEFINGS; ETC. I LOOKED UP TO SEE THAT THE CAPT HAD TAXIED ONTO RWY 2 AND HAD NOT HELD SHORT AS INSTRUCTED. HE MADE A 180 DEG TURN AND RETURNED TO POINT 'A' HOLD SHORT LINE. GND THEN TOLD US TO CONTACT TWR 118.7. WE DID. TWR NEVER SAID ANYTHING TO US CONCERNING THE EVENT AT ALL. ANOTHER ACFT TURNING TO POS AND HOLD ON THAT RWY WAS NO FACTOR; NOR DID THEY SAY ANYTHING. I BELIEVE AIRLINES SHOULD PUT TAPE RECORDERS ON SMALL ACFT TO DO PAX SAFETY BRIEFINGS; IF NO FLT ATTENDANT IS REQUIRED; OR CHANGE CHKLIST. THE FO NEEDS TO BE HEADS UP TO ASSIST THE CAPT AND AS A SECOND SET OF EYES. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THE CONSTRUCTION CREATED A PROBLEM AS ACFT HAD TO BACK TAXI DOWN RWY FOR TKOF. RWY TRANSGRESSION WAS DISCOVERED AS ACFT ALREADY ON RWY REACHED TURN AROUND POINT AND RPTR ACFT WAS OFF THE RWY PRIOR TO SECOND ACFT BEING IN POS FOR TKOF. GND CTLR APPARENTLY NOT AWARE OF RWY TRANSGRESSION SINCE THEY GOT OFF SO QUICKLY.