Narrative:

This was a typical 'race' to get departed prior to thunderstorms arriving. There were cumulonimbus both north and west of ord, and only southeast departures were going. Many airplanes sitting on txwys and ramps. We were hustled down taxiway D to runway 22L for departure. The WX was approaching quickly from the north, and was over runway 27R, 'north side of field' as we approached runway 22L. The sky was black as night. But south was clear, and a runway 22L with a left turn, (standard departure for ord-bos) looked ok. The wind was picking up as we were cleared for takeoff, and I thought the tower said the wind was 270 degrees versus 340 degrees at 16 KTS. I changed maximum power, tailwind, and told first officer to continue takeoff. We had a jump seat rider who later told us the tower announced the wind as 020 degrees at 20 KTS as we started roll. I either didn't hear this or didn't register it. Takeoff performance was somewhat degraded, definitely a tailwind. We rotated at the 2000 ft to go marker and broke ground with about 1000 ft to go. Although the maximum power covered the tailwind restr, and we were below the tailwind limit, I never thought about the runway limit penalty with a tailwind. The penalty was 1300 ft per KT. We later determined that at the wind of 340 degrees at 16 KTS, we were 8400 pounds over the runway limit. Obviously at 020 degrees at 20 KTS, it was even much more. I don't know what I was thinking. This WX was moving so fast there is no way that the takeoff should have been commenced. It was black and it was gusty and I was thinking of getting the job done, getting home, and getting the people out of ord before the WX hits, and safety was compromised.

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Original NASA ASRS Text

Title: B737 FLT CREW EXECUTES A TKOF WITH THE ACFT EXCEEDING THE RWY LIMIT FROM ORD.

Narrative: THIS WAS A TYPICAL 'RACE' TO GET DEPARTED PRIOR TO TSTMS ARRIVING. THERE WERE CUMULONIMBUS BOTH N AND W OF ORD, AND ONLY SE DEPS WERE GOING. MANY AIRPLANES SITTING ON TXWYS AND RAMPS. WE WERE HUSTLED DOWN TXWY D TO RWY 22L FOR DEP. THE WX WAS APCHING QUICKLY FROM THE N, AND WAS OVER RWY 27R, 'N SIDE OF FIELD' AS WE APCHED RWY 22L. THE SKY WAS BLACK AS NIGHT. BUT S WAS CLR, AND A RWY 22L WITH A L TURN, (STANDARD DEP FOR ORD-BOS) LOOKED OK. THE WIND WAS PICKING UP AS WE WERE CLRED FOR TKOF, AND I THOUGHT THE TWR SAID THE WIND WAS 270 DEGS VERSUS 340 DEGS AT 16 KTS. I CHANGED MAX PWR, TAILWIND, AND TOLD FO TO CONTINUE TKOF. WE HAD A JUMP SEAT RIDER WHO LATER TOLD US THE TWR ANNOUNCED THE WIND AS 020 DEGS AT 20 KTS AS WE STARTED ROLL. I EITHER DIDN'T HEAR THIS OR DIDN'T REGISTER IT. TKOF PERFORMANCE WAS SOMEWHAT DEGRADED, DEFINITELY A TAILWIND. WE ROTATED AT THE 2000 FT TO GO MARKER AND BROKE GND WITH ABOUT 1000 FT TO GO. ALTHOUGH THE MAX PWR COVERED THE TAILWIND RESTR, AND WE WERE BELOW THE TAILWIND LIMIT, I NEVER THOUGHT ABOUT THE RWY LIMIT PENALTY WITH A TAILWIND. THE PENALTY WAS 1300 FT PER KT. WE LATER DETERMINED THAT AT THE WIND OF 340 DEGS AT 16 KTS, WE WERE 8400 LBS OVER THE RWY LIMIT. OBVIOUSLY AT 020 DEGS AT 20 KTS, IT WAS EVEN MUCH MORE. I DON'T KNOW WHAT I WAS THINKING. THIS WX WAS MOVING SO FAST THERE IS NO WAY THAT THE TKOF SHOULD HAVE BEEN COMMENCED. IT WAS BLACK AND IT WAS GUSTY AND I WAS THINKING OF GETTING THE JOB DONE, GETTING HOME, AND GETTING THE PEOPLE OUT OF ORD BEFORE THE WX HITS, AND SAFETY WAS COMPROMISED.

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.