Narrative:

Clearance was received from iah ground control by my first officer after clearing runway 26 on the high speed taxiway, to taxi via 'left turn na, right turn nk and hold short nb, contact ramp control before reaching nk.' for clearance into the international ramp area. I also heard and understood the clearance. I taxied east on na while my first officer accomplished the after landing checklist. I then turned down the volume to a lower level on the #1 radio. This was the radio in which I was monitoring ground control in order to also hear the conversation between my first officer and the ramp controller. As I turned south on nk towards the ramp, I heard that we were cleared into the ramp by the ramp controller. This clearance was relayed verbally to me by my first officer as well. I was of the understanding that airport traffic between the ramp and the local ground controller was coordination. I am mistaken on this account because as I maneuvered the aircraft across nb, I overheard the ground controller advising an air carrier aircraft exiting the ramp area caution for the inbound B737 that was not talking to him (ground control). There is confusion in my mind as to what area is controled by each controller and when and where frequency changes are to be taking place. There is nothing on our airport diagrams that depict where the different jurisdictions are located. As more and more airports are using ramp controllers, this type of situation has the potential of creating a ground collision. Airport diagrams that depict areas that are controled by local ground control and ramp control would be helpful as well as specific instructions by ground controllers and ramp controllers when or where to change frequencys. Sits where the captain must monitor 2 radio conversations is unsatisfactory. Possible contributing factors may include my desire to accomplish a timely gate arrival. I also should have taken the opportunity to call the tower and explain my confusion and actions. I don't believe fatigue was a factor, however, I had just flown from fll to lga and then to iah, with a duty time of just over 9 hours. Supplemental information from acn 511833: apparently (I didn't hear it, since I was on communication #2), ground said something to the effect that he had not cleared us across nb. There was no traffic in sight to us on nb.

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Original NASA ASRS Text

Title: B737-300 PIC TAXIES IN TO THE RAMP AFTER HE HAD BEEN TOLD TO HOLD SHORT OF THAT AREA BY GND CTLR AT IAH, TX.

Narrative: CLRNC WAS RECEIVED FROM IAH GND CTL BY MY FO AFTER CLRING RWY 26 ON THE HIGH SPD TXWY, TO TAXI VIA 'L TURN NA, R TURN NK AND HOLD SHORT NB, CONTACT RAMP CTL BEFORE REACHING NK.' FOR CLRNC INTO THE INTL RAMP AREA. I ALSO HEARD AND UNDERSTOOD THE CLRNC. I TAXIED E ON NA WHILE MY FO ACCOMPLISHED THE AFTER LNDG CHKLIST. I THEN TURNED DOWN THE VOLUME TO A LOWER LEVEL ON THE #1 RADIO. THIS WAS THE RADIO IN WHICH I WAS MONITORING GND CTL IN ORDER TO ALSO HEAR THE CONVERSATION BTWN MY FO AND THE RAMP CTLR. AS I TURNED S ON NK TOWARDS THE RAMP, I HEARD THAT WE WERE CLRED INTO THE RAMP BY THE RAMP CTLR. THIS CLRNC WAS RELAYED VERBALLY TO ME BY MY FO AS WELL. I WAS OF THE UNDERSTANDING THAT ARPT TFC BTWN THE RAMP AND THE LCL GND CTLR WAS COORD. I AM MISTAKEN ON THIS ACCOUNT BECAUSE AS I MANEUVERED THE ACFT ACROSS NB, I OVERHEARD THE GND CTLR ADVISING AN ACR ACFT EXITING THE RAMP AREA CAUTION FOR THE INBOUND B737 THAT WAS NOT TALKING TO HIM (GND CTL). THERE IS CONFUSION IN MY MIND AS TO WHAT AREA IS CTLED BY EACH CTLR AND WHEN AND WHERE FREQ CHANGES ARE TO BE TAKING PLACE. THERE IS NOTHING ON OUR ARPT DIAGRAMS THAT DEPICT WHERE THE DIFFERENT JURISDICTIONS ARE LOCATED. AS MORE AND MORE ARPTS ARE USING RAMP CTLRS, THIS TYPE OF SIT HAS THE POTENTIAL OF CREATING A GND COLLISION. ARPT DIAGRAMS THAT DEPICT AREAS THAT ARE CTLED BY LCL GND CTL AND RAMP CTL WOULD BE HELPFUL AS WELL AS SPECIFIC INSTRUCTIONS BY GND CTLRS AND RAMP CTLRS WHEN OR WHERE TO CHANGE FREQS. SITS WHERE THE CAPT MUST MONITOR 2 RADIO CONVERSATIONS IS UNSATISFACTORY. POSSIBLE CONTRIBUTING FACTORS MAY INCLUDE MY DESIRE TO ACCOMPLISH A TIMELY GATE ARR. I ALSO SHOULD HAVE TAKEN THE OPPORTUNITY TO CALL THE TWR AND EXPLAIN MY CONFUSION AND ACTIONS. I DON'T BELIEVE FATIGUE WAS A FACTOR, HOWEVER, I HAD JUST FLOWN FROM FLL TO LGA AND THEN TO IAH, WITH A DUTY TIME OF JUST OVER 9 HRS. SUPPLEMENTAL INFO FROM ACN 511833: APPARENTLY (I DIDN'T HEAR IT, SINCE I WAS ON COM #2), GND SAID SOMETHING TO THE EFFECT THAT HE HAD NOT CLRED US ACROSS NB. THERE WAS NO TFC IN SIGHT TO US ON NB.

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.