Narrative:

While waiting #1 for takeoff at sjc runway 30L, we watched several arrival aircraft for spacing and anticipated clearance onto the runway. I heard what I thought was our call sign, 'cleared into position and hold.' I acknowledged tower's call and we taxied onto the runway from taxiway B1. As we pulled into position, I saw a private beech 1900 also taxi into position further down the runway from taxiway C on the west side of the airport. About this time tower called asking if we were taxiing onto the runway and I answered, 'yes, we were.' tower told us to clear the runway at taxiway B, which we did. The beech 1900 was cleared for takeoff, an air carrier landed, another air carrier was cleared for takeoff and then we were cleared for takeoff. There was no conflict inbound traffic that I am aware of. We were on and off the runway in under a minute and safety was never an issue but my anticipation of being cleared onto the runway and our recent change from 3 digit call signs to 4 digit call signs caused me to answer to another aircraft's clearance and taxi onto an active runway without clearance. Tower's query was my first indication of what had happened. Listening more closely to radio transmission and questioning the controling agency if any doubt about a radio call would have prevented this.

Related reports:

Google
 

Original NASA ASRS Text

Title: AN ACR FLC HAS PROBS WITH CALL SIGN CONFUSION AND TAXIES ONTO THE ACTIVE RWY WITHOUT CLRNC AT SJC, CA.

Narrative: WHILE WAITING #1 FOR TKOF AT SJC RWY 30L, WE WATCHED SEVERAL ARR ACFT FOR SPACING AND ANTICIPATED CLRNC ONTO THE RWY. I HEARD WHAT I THOUGHT WAS OUR CALL SIGN, 'CLRED INTO POS AND HOLD.' I ACKNOWLEDGED TWR'S CALL AND WE TAXIED ONTO THE RWY FROM TXWY B1. AS WE PULLED INTO POS, I SAW A PVT BEECH 1900 ALSO TAXI INTO POS FURTHER DOWN THE RWY FROM TXWY C ON THE W SIDE OF THE ARPT. ABOUT THIS TIME TWR CALLED ASKING IF WE WERE TAXIING ONTO THE RWY AND I ANSWERED, 'YES, WE WERE.' TWR TOLD US TO CLR THE RWY AT TXWY B, WHICH WE DID. THE BEECH 1900 WAS CLRED FOR TKOF, AN ACR LANDED, ANOTHER ACR WAS CLRED FOR TKOF AND THEN WE WERE CLRED FOR TKOF. THERE WAS NO CONFLICT INBOUND TFC THAT I AM AWARE OF. WE WERE ON AND OFF THE RWY IN UNDER A MINUTE AND SAFETY WAS NEVER AN ISSUE BUT MY ANTICIPATION OF BEING CLRED ONTO THE RWY AND OUR RECENT CHANGE FROM 3 DIGIT CALL SIGNS TO 4 DIGIT CALL SIGNS CAUSED ME TO ANSWER TO ANOTHER ACFT'S CLRNC AND TAXI ONTO AN ACTIVE RWY WITHOUT CLRNC. TWR'S QUERY WAS MY FIRST INDICATION OF WHAT HAD HAPPENED. LISTENING MORE CLOSELY TO RADIO XMISSION AND QUESTIONING THE CTLING AGENCY IF ANY DOUBT ABOUT A RADIO CALL WOULD HAVE PREVENTED THIS.

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.