Air carrier departure from pdx aborts takeoff when tower instructions are garbled.

Attributes
ACN	597582
Time
Date	200310
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : pdx.airport
State Reference	OR
Altitude	agl single value : 0
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Flight Phase	ground : takeoff roll
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : commercial pilot : instrument
ASRS Report	597582
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	597581
Events
Anomaly	other anomaly other
Independent Detector	other flight crewa other flight crewb
Resolutory Action	controller : issued new clearance flight crew : rejected takeoff
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	ATC Human Performance Flight Crew Human Performance Navigational Facility
Primary Problem	Ambiguous
Air Traffic Incident	other

Narrative:

Pdx tower advised us of company traffic on 6 mi final and cleared for takeoff. We taxied into position and began the takeoff roll without undue delay. As power was approximately 75% and increasing, airspeed had not registered yet, tower transmitted 'air carrier X do not delay departure.' this transmission was partially garbled and the captain and I were uncertain at that point if we had been cleared for takeoff or not. All we heard was 'do not departure' so the captain decided to abort the takeoff. We were able to turn off on taxiway A2, which is the first taxiway after taking the runway. We queried tower as to whether we had been cleared for takeoff or not and they said we had. Captain called pdx tower upon arrival in den and they apologized for the unnecessary call and improper phraseology.

Original NASA ASRS Text

Title: ACR DEP FROM PDX ABORTS TKOF WHEN TWR INSTRUCTIONS ARE GARBLED.

Narrative: PDX TWR ADVISED US OF COMPANY TFC ON 6 MI FINAL AND CLRED FOR TKOF. WE TAXIED INTO POS AND BEGAN THE TKOF ROLL WITHOUT UNDUE DELAY. AS PWR WAS APPROX 75% AND INCREASING, AIRSPD HAD NOT REGISTERED YET, TWR XMITTED 'ACR X DO NOT DELAY DEP.' THIS XMISSION WAS PARTIALLY GARBLED AND THE CAPT AND I WERE UNCERTAIN AT THAT POINT IF WE HAD BEEN CLRED FOR TKOF OR NOT. ALL WE HEARD WAS 'DO NOT DEP' SO THE CAPT DECIDED TO ABORT THE TKOF. WE WERE ABLE TO TURN OFF ON TXWY A2, WHICH IS THE FIRST TXWY AFTER TAKING THE RWY. WE QUERIED TWR AS TO WHETHER WE HAD BEEN CLRED FOR TKOF OR NOT AND THEY SAID WE HAD. CAPT CALLED PDX TWR UPON ARR IN DEN AND THEY APOLOGIZED FOR THE UNNECESSARY CALL AND IMPROPER PHRASEOLOGY.

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.