Narrative:

We received taxi clearance to taxi to runway 27L via taxiway T, hold short of runway 27L and follow the 'rj.' while I was updating the FMC, the aircraft in front of the rj verified that they were cleared to cross the runway. The aircraft continued and the rj followed the first aircraft. I informed the captain that I was once again 'heads up' and asked if we were cleared to cross runway 27L. He informed me that we were cleared to cross. I informed him I did not hear the clearance due to performing other duties. He once again informed me that we were to follow the rj and that he was cleared to cross the runway. We cleared the runway and proceeded to cross. Upon reaching the other side of the runway, we were informed that we in fact did not have clearance to cross runway 27L. We apologized due to frequency congestion. We were unable to ask for clarification. If giving instructions to follow aircraft around should advise each aircraft individually. Instructions to follow or cross intxns. Supplemental information from acn 476307: ground control very busy with delays outbound due to WX. Our clearance was to runway 27L, follow the' rj.' we were then told to monitor tower frequency. A combination of 'perceived' taxi clearance, other communications, a clear runway all led to this crossing without clearance. In a 'perfect' world, each aircraft should receive its own clearance. The same congestion on frequency that led the controller to give the 'follow' clearance also led us to cross without verifying. In the future, I will always verify clearance to cross a runway.

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Original NASA ASRS Text

Title: AN ACR TWIN JET FOLLOWS AN RJ ACROSS RWY 27L WHEN THEIR INITIAL CLRNC HAD BEEN TO 'HOLD SHORT OF RWY 27L, FOLLOW THE RJ.'

Narrative: WE RECEIVED TAXI CLRNC TO TAXI TO RWY 27L VIA TXWY T, HOLD SHORT OF RWY 27L AND FOLLOW THE 'RJ.' WHILE I WAS UPDATING THE FMC, THE ACFT IN FRONT OF THE RJ VERIFIED THAT THEY WERE CLRED TO CROSS THE RWY. THE ACFT CONTINUED AND THE RJ FOLLOWED THE FIRST ACFT. I INFORMED THE CAPT THAT I WAS ONCE AGAIN 'HEADS UP' AND ASKED IF WE WERE CLRED TO CROSS RWY 27L. HE INFORMED ME THAT WE WERE CLRED TO CROSS. I INFORMED HIM I DID NOT HEAR THE CLRNC DUE TO PERFORMING OTHER DUTIES. HE ONCE AGAIN INFORMED ME THAT WE WERE TO FOLLOW THE RJ AND THAT HE WAS CLRED TO CROSS THE RWY. WE CLRED THE RWY AND PROCEEDED TO CROSS. UPON REACHING THE OTHER SIDE OF THE RWY, WE WERE INFORMED THAT WE IN FACT DID NOT HAVE CLRNC TO CROSS RWY 27L. WE APOLOGIZED DUE TO FREQ CONGESTION. WE WERE UNABLE TO ASK FOR CLARIFICATION. IF GIVING INSTRUCTIONS TO FOLLOW ACFT AROUND SHOULD ADVISE EACH ACFT INDIVIDUALLY. INSTRUCTIONS TO FOLLOW OR CROSS INTXNS. SUPPLEMENTAL INFO FROM ACN 476307: GND CTL VERY BUSY WITH DELAYS OUTBOUND DUE TO WX. OUR CLRNC WAS TO RWY 27L, FOLLOW THE' RJ.' WE WERE THEN TOLD TO MONITOR TWR FREQ. A COMBINATION OF 'PERCEIVED' TAXI CLRNC, OTHER COMS, A CLR RWY ALL LED TO THIS XING WITHOUT CLRNC. IN A 'PERFECT' WORLD, EACH ACFT SHOULD RECEIVE ITS OWN CLRNC. THE SAME CONGESTION ON FREQ THAT LED THE CTLR TO GIVE THE 'FOLLOW' CLRNC ALSO LED US TO CROSS WITHOUT VERIFYING. IN THE FUTURE, I WILL ALWAYS VERIFY CLRNC TO CROSS A RWY.

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.