Flight crew of an heavy transport took off without takeoff clearance.

Attributes
ACN	301813
Time
Date	199504
Day	Sat
Local Time Of Day	0001 To 0600
Place
Locale Reference	airport : bru
State Reference	FO
Altitude	agl bound lower : 0 agl bound upper : 0
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	DC-8 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	climbout : takeoff
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : second officer
Qualification	pilot : flight engineer pilot : atp pilot : commercial pilot : instrument
Experience	flight time last 90 days : 120 flight time total : 4700 flight time type : 400
ASRS Report	301813
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	non adherence : clearance other anomaly other
Independent Detector	other controllera
Resolutory Action	none taken : detected after the fact other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

As we were taxiing for departure at brussels national the tower controller cleared us to 'line up runway 25R.' as we lined up on runway 25R the captain brought the thrust levers up and called out 'set takeoff thrust.' the first officer complied and we accelerated down the runway. As we lifted off, brussels tower called us and requested that next time we wait for our takeoff clearance. The captain and first officer had assumed we were cleared for takeoff. I was performing IOE instruction while occupying one of the jumpseats and had experienced problems with my headset while taxiing out. I switched headphone jacks just before takeoff and I assumed that I had missed the clearance. This is a classic case of 4 relatively experienced pilots hearing (or assuming) what they expected to hear - not what was actually said. I also feel that the phraseology 'cleared to line up runway 25R' is easily confused with 'cleared to takeoff runway 25R.' 'taxi into position and hold' is a clearance that is not so easily confused, especially for united states pilots. In the future I will question a clearance if I did not hear or understand all of it. It is dangerous to assume that all of the other cockpit crew heard and understand the clearance.

Original NASA ASRS Text

Title: FLC OF AN HVT TOOK OFF WITHOUT TKOF CLRNC.

Narrative: AS WE WERE TAXIING FOR DEP AT BRUSSELS NATIONAL THE TWR CTLR CLRED US TO 'LINE UP RWY 25R.' AS WE LINED UP ON RWY 25R THE CAPT BROUGHT THE THRUST LEVERS UP AND CALLED OUT 'SET TKOF THRUST.' THE FO COMPLIED AND WE ACCELERATED DOWN THE RWY. AS WE LIFTED OFF, BRUSSELS TWR CALLED US AND REQUESTED THAT NEXT TIME WE WAIT FOR OUR TKOF CLRNC. THE CAPT AND FO HAD ASSUMED WE WERE CLRED FOR TKOF. I WAS PERFORMING IOE INSTRUCTION WHILE OCCUPYING ONE OF THE JUMPSEATS AND HAD EXPERIENCED PROBS WITH MY HEADSET WHILE TAXIING OUT. I SWITCHED HEADPHONE JACKS JUST BEFORE TKOF AND I ASSUMED THAT I HAD MISSED THE CLRNC. THIS IS A CLASSIC CASE OF 4 RELATIVELY EXPERIENCED PLTS HEARING (OR ASSUMING) WHAT THEY EXPECTED TO HEAR - NOT WHAT WAS ACTUALLY SAID. I ALSO FEEL THAT THE PHRASEOLOGY 'CLRED TO LINE UP RWY 25R' IS EASILY CONFUSED WITH 'CLRED TO TKOF RWY 25R.' 'TAXI INTO POS AND HOLD' IS A CLRNC THAT IS NOT SO EASILY CONFUSED, ESPECIALLY FOR UNITED STATES PLTS. IN THE FUTURE I WILL QUESTION A CLRNC IF I DID NOT HEAR OR UNDERSTAND ALL OF IT. IT IS DANGEROUS TO ASSUME THAT ALL OF THE OTHER COCKPIT CREW HEARD AND UNDERSTAND THE 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.