Narrative:

Air carrier Y cleared for takeoff runway 27R with another aircraft (light transport) on a 2 mi final for runway 27R. Air carrier X landed on runway 27L initially told to hold short of runway 27R. Air carrier Y was rolling on runway 27R. I felt that air carrier Y would be airborne and no factor for air carrier X and that air carrier X could beat the light transport on final across the runway. I cleared air carrier X to cross runway 27R. Air carrier X got to the intersection (tango) quicker than I anticipated and air carrier Y overflew (by several hundred ft) the air carrier X. The pilots did everything as directed, the error was a result of my anticipating sep rather than ensuring sep by using positive control. I should have held the air carrier X short of runway 27R as I had originally planned and waited until the air carrier Y passed the intersection, even if it meant holding the air carrier X until the light transport landed. Supplemental information from acn 147529. Air carrier X arrived atl, landed west/O incident on runway 27L. Tower advised initially to 'hold short' of runway 27R and then revised their instructions to 'if you'll expedite, you're cleared to cross runway 27R. Traffic 1 1/2 mi final'. We acknowledged, pushed power up to expedite crossing. There is a slight hump in runway 27R that blocks a clear view of the east end. There appeared to be traffic holding in position (only tail visible). Both first officer and I checked runway and saw light transport on final. About 1/2 way across the runway, I again checked the runway (looking across cockpit from left to right) and the holding traffic appeared to be moving side to side, indicating forward movement. Just then its nose rotated and the nose light of air carrier Y, medium large transport became visable. I applied additional power to hasten clearing the runway. Aircraft were not closer than 2000' while we were on the runway. Through informal channels, we have learned that air carrier Y had been cleared for takeoff prior to our post landing contact with tower. Atl tower has acknowledged a controller error. It seems that having cleared air carrier Y for takeoff the controller put air carrier Y 'out of mind' and concentrated on trying to expedite our progress to the terminal. Our rapport and cooperation with atl ATC is excellent and our only interest is analyzing the breakdown to prevent a recurrence.

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Original NASA ASRS Text

Title: ACR X HAD LESS THAN STANDARD SEPARATION FROM ACR Y. SYSTEM ERROR.

Narrative: ACR Y CLRED FOR TKOF RWY 27R WITH ANOTHER ACFT (LTT) ON A 2 MI FINAL FOR RWY 27R. ACR X LANDED ON RWY 27L INITIALLY TOLD TO HOLD SHORT OF RWY 27R. ACR Y WAS ROLLING ON RWY 27R. I FELT THAT ACR Y WOULD BE AIRBORNE AND NO FACTOR FOR ACR X AND THAT ACR X COULD BEAT THE LTT ON FINAL ACROSS THE RWY. I CLRED ACR X TO CROSS RWY 27R. ACR X GOT TO THE INTXN (TANGO) QUICKER THAN I ANTICIPATED AND ACR Y OVERFLEW (BY SEVERAL HUNDRED FT) THE ACR X. THE PLTS DID EVERYTHING AS DIRECTED, THE ERROR WAS A RESULT OF MY ANTICIPATING SEP RATHER THAN ENSURING SEP BY USING POSITIVE CTL. I SHOULD HAVE HELD THE ACR X SHORT OF RWY 27R AS I HAD ORIGINALLY PLANNED AND WAITED UNTIL THE ACR Y PASSED THE INTXN, EVEN IF IT MEANT HOLDING THE ACR X UNTIL THE LTT LANDED. SUPPLEMENTAL INFO FROM ACN 147529. ACR X ARRIVED ATL, LANDED W/O INCIDENT ON RWY 27L. TWR ADVISED INITIALLY TO 'HOLD SHORT' OF RWY 27R AND THEN REVISED THEIR INSTRUCTIONS TO 'IF YOU'LL EXPEDITE, YOU'RE CLRED TO CROSS RWY 27R. TFC 1 1/2 MI FINAL'. WE ACKNOWLEDGED, PUSHED PWR UP TO EXPEDITE XING. THERE IS A SLIGHT HUMP IN RWY 27R THAT BLOCKS A CLR VIEW OF THE E END. THERE APPEARED TO BE TFC HOLDING IN POS (ONLY TAIL VISIBLE). BOTH F/O AND I CHKED RWY AND SAW LTT ON FINAL. ABOUT 1/2 WAY ACROSS THE RWY, I AGAIN CHKED THE RWY (LOOKING ACROSS COCKPIT FROM L TO R) AND THE HOLDING TFC APPEARED TO BE MOVING SIDE TO SIDE, INDICATING FORWARD MOVEMENT. JUST THEN ITS NOSE ROTATED AND THE NOSE LIGHT OF ACR Y, MLG BECAME VISABLE. I APPLIED ADDITIONAL PWR TO HASTEN CLRING THE RWY. ACFT WERE NOT CLOSER THAN 2000' WHILE WE WERE ON THE RWY. THROUGH INFORMAL CHANNELS, WE HAVE LEARNED THAT ACR Y HAD BEEN CLRED FOR TKOF PRIOR TO OUR POST LNDG CONTACT WITH TWR. ATL TWR HAS ACKNOWLEDGED A CTLR ERROR. IT SEEMS THAT HAVING CLRED ACR Y FOR TKOF THE CTLR PUT ACR Y 'OUT OF MIND' AND CONCENTRATED ON TRYING TO EXPEDITE OUR PROGRESS TO THE TERMINAL. OUR RAPPORT AND COOPERATION WITH ATL ATC IS EXCELLENT AND OUR ONLY INTEREST IS ANALYZING THE BREAKDOWN TO PREVENT A RECURRENCE.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.