AN ACR ACFT WAS CLRED FOR TKOF ON A TWR FREQ DIFFERENT FROM THE FREQ AN ACR ACFT WAS USING WHEN IT WAS CLRED TO CROSS THE RWY. THE DEPARTING ACFT CROSSED OVER THE TAXIING ACFT AT APPROX 400 FT. AN ATC ERROR WAS ADMITTED.

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CLRED 'POS AND HOLD' ON RWY 27R WHILE COMPLETING CHKLISTS AND ACFT WERE XING DOWNFIELD. AFTER ABOUT 1 MIN AND AFTER ALL OBVIOUS ACFT HAD CROSSED; WERE CLRED FOR TKOF WITH AN ASSIGNED HDG. I (PIC -- CHK AIRMAN) WAS FLYING FROM R SEAT. TKOF WAS NORMAL; WITH CLR RWY AHEAD. SHORTLY AFTER ROTATION AND LIFTOFF; PNF IN L SEAT CALLED ACFT XING ON RWY. I NOTED INTRUDING ACFT ABOUT 1/2 MI AHEAD; AND REALIZED WE WOULD BE WELL CLR. I MADE A BRIEF RADIO CALL: 'YOU'VE GOT A RWY XING...' OR WORDS TO THAT EFFECT. WE PASSED ABOUT 400 FT ABOVE THE ACFT AS IT WAS CLRING THE RWY L TO R. WE CONTINUED A NORMAL DEP; AND WERE LATER ASKED TO CALL TWR BY PHONE AFTER ARR. IN SUBSEQUENT PHONE CALL WITH TWR; THE TWR REPRESENTATIVE STATED THAT THE TWR HAD MADE AN OPERROR. THE TXWY N5 XING OF RWY 27R IS SOMEWHAT RESTR. ACFT TAXIING W ON TXWY N; AND MAKING A R TURN AT N5 TO HOLD SHORT OF THE RWY WILL NORMALLY BE ANGLED NW; AND UNABLE TO SEE THE APCH END OF RWY 27R UNTIL THEY BEGIN TO CROSS THE HOLD LINE. THUS IT IS DIFFICULT TO VISUALLY ASSURE A CLR RWY UNTIL THE ACFT HAS CROSSED THE HOLD LINE AND IS MORE PERPENDICULAR TO THE RWY. PERHAPS THE TAXI AND HOLD LINES AT N5 COULD BE MODIFIED TO ALLOW ACFT TO 'SQUARE UP' AND SEE DOWN THE RWY BEFORE XING THE HOLD LINE. OTHERWISE; A LIGHT SIGNAL SYS LIKE AT DFW SHOULD BE INSTALLED. SUPPLEMENTAL INFO FROM ACN 774959: AFTER LNDG ON RWY 27L WHILE CLRING THE RWY; TWR CTLR ON FREQ X TOLD US 'CROSS RWY 27R AT TANGO; MONITOR FREQ Y.' FO ACKNOWLEDGED 'CROSS RWY 27R AT TANGO; FREQ Y.' WE SWITCHED OVER TO FREQ Y AND AS WE APCHED THE INTXN OF TANGO AND RWY 27R WE CONFIRMED WITH EACH OTHER THAT WE WERE CLRED TO CROSS AND THAT THE ACFT AT THE DEP END APPEARED TO BE HOLDING POS. AS WE CLRED THE RWY AT THE OTHER SIDE; THE TWR CTLR ADVISED THAT WE HAD JUST CROSSED THE WITHOUT PERMISSION. WE TOLD THE TWR THAT THE CTLR ON FREQ X HAD CLRED US TO CROSS. TWR THEN SWITCHED US TO GND WHO GAVE US A PHONE NUMBER TO CALL. WHEN WE ARRIVED AT THE GATE; WE CALLED THE TWR ON THE PHONE AND THE TWR ADVISED US AFTER LISTENING TO THE TAPE THAT THE CTLR HAD IN FACT CLRED US TO CROSS RWY 27R; WE HAD READ IT BACK; AND THAT THE INCIDENT WAS THEIR FAULT.