Narrative:

While taxiing to runway 17 at grr, flight X (light transport), grr to mke, completed the before takeoff checklist. While the captain taxied, the first officer read the checklist. After completing the checklist, and while still taxiing, we were cleared into position and hold (on runway 17). It is our company procedure to execute the takeoff final items checklist as we taxi into position, which we performed normally. At the completion of the checklist, I began to add power and begin my takeoff roll. Shortly after, my first officer expressed concern that we may not have been cleared for takeoff. I replied that we were issued a heading, so we must have been cleared. I elected to continue the takeoff normally. Climbing through 400 ft, tower announced 'air carrier light transport, I see that you took off, I'm not sure that I cleared you...maintain runway heading and 3000 ft.' the best way to have avoided this situation would have been to exercise better cockpit discipline in listening to clrncs and not what I expected to hear. In addition, my copilot stated uncertainty in my action, and I should have committed to a low speed abort and taxi back -- even if I was correct about the clearance. (I believe I heard '...runway 17...' and mistook it for a heading of 170 degrees, which led me to believe that we had been given a takeoff clearance.)

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Original NASA ASRS Text

Title: CAPT ON BE02 ACR FLT AT GRR IS CLRED INTO POS AND HOLD, COMPLETES CHKLIST AND TAKES OFF.

Narrative: WHILE TAXIING TO RWY 17 AT GRR, FLT X (LTT), GRR TO MKE, COMPLETED THE BEFORE TKOF CHKLIST. WHILE THE CAPT TAXIED, THE FO READ THE CHKLIST. AFTER COMPLETING THE CHKLIST, AND WHILE STILL TAXIING, WE WERE CLRED INTO POS AND HOLD (ON RWY 17). IT IS OUR COMPANY PROC TO EXECUTE THE TKOF FINAL ITEMS CHKLIST AS WE TAXI INTO POS, WHICH WE PERFORMED NORMALLY. AT THE COMPLETION OF THE CHKLIST, I BEGAN TO ADD PWR AND BEGIN MY TKOF ROLL. SHORTLY AFTER, MY FO EXPRESSED CONCERN THAT WE MAY NOT HAVE BEEN CLRED FOR TKOF. I REPLIED THAT WE WERE ISSUED A HDG, SO WE MUST HAVE BEEN CLRED. I ELECTED TO CONTINUE THE TKOF NORMALLY. CLBING THROUGH 400 FT, TWR ANNOUNCED 'ACR LTT, I SEE THAT YOU TOOK OFF, I'M NOT SURE THAT I CLRED YOU...MAINTAIN RWY HDG AND 3000 FT.' THE BEST WAY TO HAVE AVOIDED THIS SIT WOULD HAVE BEEN TO EXERCISE BETTER COCKPIT DISCIPLINE IN LISTENING TO CLRNCS AND NOT WHAT I EXPECTED TO HEAR. IN ADDITION, MY COPLT STATED UNCERTAINTY IN MY ACTION, AND I SHOULD HAVE COMMITTED TO A LOW SPD ABORT AND TAXI BACK -- EVEN IF I WAS CORRECT ABOUT THE CLRNC. (I BELIEVE I HEARD '...RWY 17...' AND MISTOOK IT FOR A HDG OF 170 DEGS, WHICH LED ME TO BELIEVE THAT WE HAD BEEN GIVEN A TKOF 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.