B737 taxiing for departure at ord enters runway without ATC clearance.

Attributes
ACN	582479
Time
Date	200305
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : ord.airport
State Reference	FL
Altitude	agl single value : 0
Environment
Flight Conditions	VMC
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Flight Phase	ground : position and hold ground : taxi
Flight Plan	IFR
Aircraft 2
Controlling Facilities	tower : iah.tower
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	ground : takeoff roll
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	582479
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : instrument pilot : commercial
ASRS Report	582355
Events
Anomaly	conflict : ground less severe incursion : runway non adherence : clearance non adherence : far
Independent Detector	other flight crewa
Resolutory Action	controller : issued new clearance
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	ATC Human Performance Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Appeared to be #1 for takeoff runway 32R ord. Heard air carrier X no delay clear for takeoff runway 32R heading 040 degrees. I read back clearance as stated and noted an air carrier Y jet on the roll runway 32R. When in position tower asked what we were doing. We replied we were cleared for takeoff. Tower advised us to hold position and soon after cleared us for takeoff. After takeoff we heard air carrier Y and realized that we may have responded to his takeoff clearance and blocked his response. I did not hear any other aircraft respond when I did. The final for runway 32R was clear and we had sight of the aircraft landing runway 27R.

Original NASA ASRS Text

Title: B737 TAXIING FOR DEP AT ORD ENTERS RWY WITHOUT ATC CLRNC.

Narrative: APPEARED TO BE #1 FOR TKOF RWY 32R ORD. HEARD ACR X NO DELAY CLR FOR TKOF RWY 32R HEADING 040 DEGS. I READ BACK CLRNC AS STATED AND NOTED AN ACR Y JET ON THE ROLL RWY 32R. WHEN IN POS TWR ASKED WHAT WE WERE DOING. WE REPLIED WE WERE CLRED FOR TKOF. TWR ADVISED US TO HOLD POS AND SOON AFTER CLRED US FOR TKOF. AFTER TKOF WE HEARD ACR Y AND REALIZED THAT WE MAY HAVE RESPONDED TO HIS TKOF CLRNC AND BLOCKED HIS RESPONSE. I DID NOT HEAR ANY OTHER ACFT RESPOND WHEN I DID. THE FINAL FOR RWY 32R WAS CLR AND WE HAD SIGHT OF THE ACFT LNDG RWY 27R.

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.