Narrative:

Ground control instructed us to taxi to runway 4R. As we taxied, ground control told us to hold short of a taxiway that xed 4R and enter the runup pad (this pad is located between 4R and 4L) and monitor tower. As we entered the runup pad, we continued to taxi to runway 4L. (Usually when instructed to cross 4R on this taxiway, it is because the departure runway was changed). We assumed that our departure runway had changed. Tower told us to taxi into position and hold. As we did this, we noticed another aircraft on the runway in position and hold. We asked the tower and they then asked our position. We said we were position and hold on runway 4L. They thought we were on runway 4R. We asked if we should exit the runway and they told us no and that we would depart momentarily, which we did west/O incidence. We should not have assumed that our departure runway had changed and expected to enter runway 4R from the other side. Clearly better crew coordination and communication with ATC would have helped. Also ATC needs better taxi instructions and the need to instruct again when confusion could occur, which runway will be used for departure. Callback conversation with reporter revealed the following information. Callback was conducted as part of a structured callback effort on runway incursions. Reporter said that he should have questioned the clearance because of its ambiguity, but that clearance was received when flight crew was running their checklist. He feels that he was reacting to the habit patterns arising from previous experience, but feels that controller could have been specific about which runway was intended.

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Original NASA ASRS Text

Title: FLC OF COMMUTER ACR DEPARTING MDW IS TOLD TO CROSS RWY 4L DURING TAXI OUT AND PRESUMES THAT TO MEAN THAT THEY WILL BE DEPARTING RWY 4R. WHEN CLEARED INTO POSITION AND HOLD, THEY TAXI ONTO RWY 4R WHEN THE CTLR INTENDED FOR THEM TO BE ON RWY 4L.

Narrative: GND CTL INSTRUCTED US TO TAXI TO RWY 4R. AS WE TAXIED, GND CTL TOLD US TO HOLD SHORT OF A TXWY THAT XED 4R AND ENTER THE RUNUP PAD (THIS PAD IS LOCATED BTWN 4R AND 4L) AND MONITOR TWR. AS WE ENTERED THE RUNUP PAD, WE CONTINUED TO TAXI TO RWY 4L. (USUALLY WHEN INSTRUCTED TO CROSS 4R ON THIS TXWY, IT IS BECAUSE THE DEP RWY WAS CHANGED). WE ASSUMED THAT OUR DEP RWY HAD CHANGED. TWR TOLD US TO TAXI INTO POS AND HOLD. AS WE DID THIS, WE NOTICED ANOTHER ACFT ON THE RWY IN POS AND HOLD. WE ASKED THE TWR AND THEY THEN ASKED OUR POS. WE SAID WE WERE POSITION AND HOLD ON RWY 4L. THEY THOUGHT WE WERE ON RWY 4R. WE ASKED IF WE SHOULD EXIT THE RWY AND THEY TOLD US NO AND THAT WE WOULD DEPART MOMENTARILY, WHICH WE DID W/O INCIDENCE. WE SHOULD NOT HAVE ASSUMED THAT OUR DEP RWY HAD CHANGED AND EXPECTED TO ENTER RWY 4R FROM THE OTHER SIDE. CLRLY BETTER CREW COORD AND COM WITH ATC WOULD HAVE HELPED. ALSO ATC NEEDS BETTER TAXI INSTRUCTIONS AND THE NEED TO INSTRUCT AGAIN WHEN CONFUSION COULD OCCUR, WHICH RWY WILL BE USED FOR DEP. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO. CALLBACK WAS CONDUCTED AS PART OF A STRUCTURED CALLBACK EFFORT ON RWY INCURSIONS. RPTR SAID THAT HE SHOULD HAVE QUESTIONED THE CLRNC BECAUSE OF ITS AMBIGUITY, BUT THAT CLRNC WAS RECEIVED WHEN FLT CREW WAS RUNNING THEIR CHKLIST. HE FEELS THAT HE WAS REACTING TO THE HABIT PATTERNS ARISING FROM PREVIOUS EXPERIENCE, BUT FEELS THAT CTLR COULD HAVE BEEN SPECIFIC ABOUT WHICH RWY WAS INTENDED.

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.