Narrative:

We landed normally on runway 22R at lax. On landing roll, we were told to exit runway 24R and hold short of runway 24L. We acknowledged the hold short instructions. A few mins later on taxiway aa, the captain asked me if we were cleared to cross runway 24L. I responded with 'yes.' once clear of runway 24L, ground control asked us to call them at the gate. Once at the gate we found out we had crossed without clearance. When the captain asked me if we were cleared to cross runway 24L (at the time I was positive we were), he caused me to begin to doubt myself. The jet was still rolling (on taxiway aa) and while I replayed the radio calls in my head, we visually cleared runway 24L from taxiway aa. We saw nothing on the runway, so we crossed. The captain continuing across put my mind at ease. As I rethink through the scenario, a few things come to mind. First, there was a lot of chatter on the radios, and secondly it was a good bit of time from the initial hold short instructions, until we were actually on taxiway aa. I do not know why we felt we were cleared to cross -- possibly all the radio chatter. What really makes me mad is when the captain asked the question and raised a small percentage of doubt, I let our visual check of the runway clear up the doubt. I should have done what I normally do, which is to verify verbally. I am mad at myself for letting the fact that the runway was clear, convince me that I was right -- when in reality I was wrong. When in doubt, verify!

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Original NASA ASRS Text

Title: A B737 FLT CREW THOUGHT THEY WERE CLRED TO CROSS RWY 24L AT LAX ONLY TO FIND OUT BY TWR THAT THEY WERE NOT.

Narrative: WE LANDED NORMALLY ON RWY 22R AT LAX. ON LNDG ROLL, WE WERE TOLD TO EXIT RWY 24R AND HOLD SHORT OF RWY 24L. WE ACKNOWLEDGED THE HOLD SHORT INSTRUCTIONS. A FEW MINS LATER ON TXWY AA, THE CAPT ASKED ME IF WE WERE CLRED TO CROSS RWY 24L. I RESPONDED WITH 'YES.' ONCE CLR OF RWY 24L, GND CTL ASKED US TO CALL THEM AT THE GATE. ONCE AT THE GATE WE FOUND OUT WE HAD CROSSED WITHOUT CLRNC. WHEN THE CAPT ASKED ME IF WE WERE CLRED TO CROSS RWY 24L (AT THE TIME I WAS POSITIVE WE WERE), HE CAUSED ME TO BEGIN TO DOUBT MYSELF. THE JET WAS STILL ROLLING (ON TXWY AA) AND WHILE I REPLAYED THE RADIO CALLS IN MY HEAD, WE VISUALLY CLRED RWY 24L FROM TXWY AA. WE SAW NOTHING ON THE RWY, SO WE CROSSED. THE CAPT CONTINUING ACROSS PUT MY MIND AT EASE. AS I RETHINK THROUGH THE SCENARIO, A FEW THINGS COME TO MIND. FIRST, THERE WAS A LOT OF CHATTER ON THE RADIOS, AND SECONDLY IT WAS A GOOD BIT OF TIME FROM THE INITIAL HOLD SHORT INSTRUCTIONS, UNTIL WE WERE ACTUALLY ON TXWY AA. I DO NOT KNOW WHY WE FELT WE WERE CLRED TO CROSS -- POSSIBLY ALL THE RADIO CHATTER. WHAT REALLY MAKES ME MAD IS WHEN THE CAPT ASKED THE QUESTION AND RAISED A SMALL PERCENTAGE OF DOUBT, I LET OUR VISUAL CHK OF THE RWY CLR UP THE DOUBT. I SHOULD HAVE DONE WHAT I NORMALLY DO, WHICH IS TO VERIFY VERBALLY. I AM MAD AT MYSELF FOR LETTING THE FACT THAT THE RWY WAS CLR, CONVINCE ME THAT I WAS RIGHT -- WHEN IN REALITY I WAS WRONG. WHEN IN DOUBT, VERIFY!

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.