Narrative:

Awaiting takeoff at runway 9L at ord. Just after an MD80 rolled on runway 9L and with traffic on final, tower instructed us to 'position and hold runway 9L, expect an immediate takeoff, traffic on a 4 mi final.' I heard the 'immediate takeoff' call and the final traffic call and looked to clear final. First officer completed the last 5 items on the checklist, but heard the position and hold call. We did not confirm with each other the takeoff clearance. He finished the takeoff checklist just as I added power to begin rolling. He noted the power and said 'we are not cleared for takeoff, just position and hold.' I stopped then noted an F100 rolling for takeoff on runway 4L at that moment. Then tower immediately cleared us for takeoff. This could have been serious, as I never heard the position words, but rather clearly heard the tower say 'immediate takeoff' and assumed that we were cleared to go. Atta boy for a sharp first officer who did not hesitate to be assertive and firm. The tower phraseology of 'expect immediate takeoff,' while not unusual, does not normally include the word 'takeoff' in the phase. Also, the 5 items left open distraction us from confirming with one another as I usually do. Fatigue was also a factor for myself. Supplemental information from acn 625878: while waiting at the departure end of runway 9L at ord, tower cleared a flight ahead of us for takeoff. Immediately after, tower instructed us to taxi into position and hold runway 9L, traffic on 3 1/2 mi final, be ready for an immediate takeoff. The captain applied power and we finished the remaining items on the mechanical checklist as we rolled into position. The amount of thrust used and the acceleration of the aircraft indicated to me that the captain thought we were cleared for an immediate takeoff. At this point, I reminded the captain that we were only cleared for 'position and hold.' the captain immediately closed the throttles and stopped the aircraft. Shortly thereafter, tower cleared us for takeoff. We made a normal and uneventful takeoff and flight to dfw. In the discussion after, the captain had said that he had heard 'cleared for immediate takeoff' in controller's initial contact with us and had thought we were cleared for takeoff and not position and hold. While there were no deviations by the tower controller or flight crew, the distraction of finishing the mechanical checklist while taking the runway, traffic on short final, and the controller's use of the word 'takeoff' in his initial communication led to a temporary misunderstanding of our actual clearance.

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Original NASA ASRS Text

Title: ORD LCL CTLR USED INCORRECT PHRASEOLOGY BY INSTRUCTING AN MD80 TO 'TAXI INTO POS AND HOLD, EXPECT AN IMMEDIATE TKOF, TFC ON A 4 MI FINAL.'

Narrative: AWAITING TKOF AT RWY 9L AT ORD. JUST AFTER AN MD80 ROLLED ON RWY 9L AND WITH TFC ON FINAL, TWR INSTRUCTED US TO 'POS AND HOLD RWY 9L, EXPECT AN IMMEDIATE TKOF, TFC ON A 4 MI FINAL.' I HEARD THE 'IMMEDIATE TKOF' CALL AND THE FINAL TFC CALL AND LOOKED TO CLR FINAL. FO COMPLETED THE LAST 5 ITEMS ON THE CHKLIST, BUT HEARD THE POS AND HOLD CALL. WE DID NOT CONFIRM WITH EACH OTHER THE TKOF CLRNC. HE FINISHED THE TKOF CHKLIST JUST AS I ADDED PWR TO BEGIN ROLLING. HE NOTED THE PWR AND SAID 'WE ARE NOT CLRED FOR TKOF, JUST POS AND HOLD.' I STOPPED THEN NOTED AN F100 ROLLING FOR TKOF ON RWY 4L AT THAT MOMENT. THEN TWR IMMEDIATELY CLRED US FOR TKOF. THIS COULD HAVE BEEN SERIOUS, AS I NEVER HEARD THE POS WORDS, BUT RATHER CLRLY HEARD THE TWR SAY 'IMMEDIATE TKOF' AND ASSUMED THAT WE WERE CLRED TO GO. ATTA BOY FOR A SHARP FO WHO DID NOT HESITATE TO BE ASSERTIVE AND FIRM. THE TWR PHRASEOLOGY OF 'EXPECT IMMEDIATE TKOF,' WHILE NOT UNUSUAL, DOES NOT NORMALLY INCLUDE THE WORD 'TKOF' IN THE PHASE. ALSO, THE 5 ITEMS LEFT OPEN DISTR US FROM CONFIRMING WITH ONE ANOTHER AS I USUALLY DO. FATIGUE WAS ALSO A FACTOR FOR MYSELF. SUPPLEMENTAL INFO FROM ACN 625878: WHILE WAITING AT THE DEP END OF RWY 9L AT ORD, TWR CLRED A FLT AHEAD OF US FOR TKOF. IMMEDIATELY AFTER, TWR INSTRUCTED US TO TAXI INTO POS AND HOLD RWY 9L, TFC ON 3 1/2 MI FINAL, BE READY FOR AN IMMEDIATE TKOF. THE CAPT APPLIED PWR AND WE FINISHED THE REMAINING ITEMS ON THE MECHANICAL CHKLIST AS WE ROLLED INTO POS. THE AMOUNT OF THRUST USED AND THE ACCELERATION OF THE ACFT INDICATED TO ME THAT THE CAPT THOUGHT WE WERE CLRED FOR AN IMMEDIATE TKOF. AT THIS POINT, I REMINDED THE CAPT THAT WE WERE ONLY CLRED FOR 'POS AND HOLD.' THE CAPT IMMEDIATELY CLOSED THE THROTTLES AND STOPPED THE ACFT. SHORTLY THEREAFTER, TWR CLRED US FOR TKOF. WE MADE A NORMAL AND UNEVENTFUL TKOF AND FLT TO DFW. IN THE DISCUSSION AFTER, THE CAPT HAD SAID THAT HE HAD HEARD 'CLRED FOR IMMEDIATE TKOF' IN CTLR'S INITIAL CONTACT WITH US AND HAD THOUGHT WE WERE CLRED FOR TKOF AND NOT POS AND HOLD. WHILE THERE WERE NO DEVS BY THE TWR CTLR OR FLT CREW, THE DISTR OF FINISHING THE MECHANICAL CHKLIST WHILE TAKING THE RWY, TFC ON SHORT FINAL, AND THE CTLR'S USE OF THE WORD 'TKOF' IN HIS INITIAL COM LED TO A TEMPORARY MISUNDERSTANDING OF OUR ACTUAL CLRNC.

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.