Narrative:

We pushed back off in phx on time. Taxied to spot X and called ground for taxi clearance. We were cleared to taxi to runway 25R. We completed all the checklists and pulled up #1 at runway 25R. Another company was behind and off to the left of us and a company Y flight was taxiing down taxiway east towards runway 25R. Neither aircraft had access to the runway. We sat at the end for a couple of mins and got impatient so the first officer called tower 'ready.' the first officer's transmission partially blocked, tower's transmission 'position and hold' (the call sign was blocked). We assumed that the clearance into position was ours and read back the clearance to tower. Tower did not catch our error when we read it back. Once in position, tower asked 'who is in position on runway 25R?' we answered, and were chastised because tower said he had cleared company Y into position and hold. No aircraft were on final, and we took off uneventfully. We were not in a hurry during taxi out. This situation boils down to the fact that I assumed the clearance was for us, instead of verifying with tower before taxiing into position and hold. I usually verify everything when in doubt, but in this case, a little laziness crept in and we were caught in the aircraft of 'assuming.' supplemental information from acn 538031: we switched to tower and waited for an arrival to land. The tower called with a call sign that ended in 'Z,' the first part was garbled, and I read back to the tower, 'company flight number into position and hold runway 25R.' we then taxied into position and hold on runway 25R. After a short delay the tower cleared a company Y flight, whose call sign ended in 'Z' for takeoff on runway 25R. Company Y responded that they were holding short of the runway. The tower then asked 'who was on the runway?' I responded with our call sign and asked if they would like us to taxi clear. He then cleared us for takeoff.

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Original NASA ASRS Text

Title: A B737-300 CREW, TAXIING FOR TKOF AT PHX, RESPONDED TO ANOTHER ACFT'S CLRNC, TAXIING INTO POS.

Narrative: WE PUSHED BACK OFF IN PHX ON TIME. TAXIED TO SPOT X AND CALLED GND FOR TAXI CLRNC. WE WERE CLRED TO TAXI TO RWY 25R. WE COMPLETED ALL THE CHKLISTS AND PULLED UP #1 AT RWY 25R. ANOTHER COMPANY WAS BEHIND AND OFF TO THE L OF US AND A COMPANY Y FLT WAS TAXIING DOWN TXWY E TOWARDS RWY 25R. NEITHER ACFT HAD ACCESS TO THE RWY. WE SAT AT THE END FOR A COUPLE OF MINS AND GOT IMPATIENT SO THE FO CALLED TWR 'READY.' THE FO'S XMISSION PARTIALLY BLOCKED, TWR'S XMISSION 'POS AND HOLD' (THE CALL SIGN WAS BLOCKED). WE ASSUMED THAT THE CLRNC INTO POS WAS OURS AND READ BACK THE CLRNC TO TWR. TWR DID NOT CATCH OUR ERROR WHEN WE READ IT BACK. ONCE IN POS, TWR ASKED 'WHO IS IN POS ON RWY 25R?' WE ANSWERED, AND WERE CHASTISED BECAUSE TWR SAID HE HAD CLRED COMPANY Y INTO POS AND HOLD. NO ACFT WERE ON FINAL, AND WE TOOK OFF UNEVENTFULLY. WE WERE NOT IN A HURRY DURING TAXI OUT. THIS SIT BOILS DOWN TO THE FACT THAT I ASSUMED THE CLRNC WAS FOR US, INSTEAD OF VERIFYING WITH TWR BEFORE TAXIING INTO POS AND HOLD. I USUALLY VERIFY EVERYTHING WHEN IN DOUBT, BUT IN THIS CASE, A LITTLE LAZINESS CREPT IN AND WE WERE CAUGHT IN THE ACFT OF 'ASSUMING.' SUPPLEMENTAL INFO FROM ACN 538031: WE SWITCHED TO TWR AND WAITED FOR AN ARR TO LAND. THE TWR CALLED WITH A CALL SIGN THAT ENDED IN 'Z,' THE FIRST PART WAS GARBLED, AND I READ BACK TO THE TWR, 'COMPANY FLT NUMBER INTO POS AND HOLD RWY 25R.' WE THEN TAXIED INTO POS AND HOLD ON RWY 25R. AFTER A SHORT DELAY THE TWR CLRED A COMPANY Y FLT, WHOSE CALL SIGN ENDED IN 'Z' FOR TKOF ON RWY 25R. COMPANY Y RESPONDED THAT THEY WERE HOLDING SHORT OF THE RWY. THE TWR THEN ASKED 'WHO WAS ON THE RWY?' I RESPONDED WITH OUR CALL SIGN AND ASKED IF THEY WOULD LIKE US TO TAXI CLR. HE THEN CLRED US FOR TKOF.

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.