COMMUTER FLC EXPERIENCES RWY INCURSION AT EFD.

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I INFORMED GND CTL WE HAD THE ATIS AND WERE READY TO TAXI. THE CTLR INQUIRED WHICH RWY WE PREFERRED AND WE REQUESTED RWY 17R. HE INFORMED US THAT THE WINDS WERE FAVORING RWY 04. WE ACCEPTED RWY 04 AND WRE INSTRUCTED TO TAXI TO RWY 04 AND HOLD SHORT OF RWY 17R. WE ACKNOWLEDGED THIS AND HELD SHORT OF RWY 17R. WE WERE THEN CLRED TO CROSS RWY 17R AND TAXI TO RWY 04. BEFORE ARRIVING AT RWY 04; THE GND CTLR INFORMED US THAT THE WIND HAD SHIFTED AND WAS 100 DEG AT 11 KTS. AFTER A BRIEF DISCUSSION; THE CAPT AND I AGREED TO STILL USE RWY 04. AS WE APCHED THE RWY; I WAS USING THE PA COMM. INSTRUCTING THE FLT ATTENDANT TO BE SEATED FOR DEP. WHEN I SWITCHED BACK OVER TO THE COMM 1 FREQ; I REALIZED THAT WE WERE TAXIING ONTO THE RWY AND WERE QUICKLY ASKED OUR POS BY THE GND CTLR. WE WERE THEN INFORMED THAT WE HAD NOT YET BEEN CLRED INTO POS. THE CAPT REALIZED HIS MISTAKE AND INFORMED ME THAT HE HAD SOMEHOW MISUNDERSTOOD THE CLRNC AFTER TALKING WITH THE CTLR ABOUT THE WIND SHIFT. I SHOULD HAVE BEEN MORE ALERT AS A CREWMEMBER AND REALIZED OUR POS. THE ONLY THING I CAN THINK OF IS THAT WHILE I BRIEFLY SWITCHED RADIOS; I ASSUMED THE CAPT HAD BEEN INSTRUCTED TO TAXI INTO POS ON THE RWY. THIS INCIDENT HAS TAUGHT ME TO BE MORE VIGILANT WHILE TAXIING AND NEVER TO ASSUME THAT THE CAPT IS ALWAYS RIGHT; ALTHOUGH THEY USUALLY ARE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR NOTED THAT THE FLT WAS UTILIZING TXWY D; AND THAT THERE HAD BEEN A CHANGE IN TAXI CLRNC THAT CONTRIBUTED SOMEWHAT TO FLC DISTR. HE REITERATED THAT THE PF HAD CAREFULLY SCANNED THAT APCH TO RWY 04 BEFORE TAXIING ONTO THE ACTIVE; AND THAT NO ACTUAL CONFLICT HAD OCCURRED. HE ALSO NOTED THAT THERE WAS POORLY MARKED CONSTRUCTION ON RWY 04; AND THAT ABOUT THE FIRST 1000 FT WAS CLOSED -- THEY WERE ADMONISHED BY THE LOCAL CTLR FOR TAXIING ONTO THIS CLOSED PORTION.