Narrative:

Incident occurred when tower directed a runway change for departures. We were next for takeoff, tower was rushing us to accept a different runway. We checked performance data and replied we wouldn't do it, too heavy. So they said we could depart on original runway if we could do so immediately. We were 12000 pounds under maximum runway limit weight. But now the winds were 20 degree off our tail at 12 KTS. I used a rule of thumb and felt that equaled 10 KTS direct tailwind, our maximum allowable. Also, I felt 12000 pounds cushion on runway limit weight was more than sufficient to cover the tailwind. To delay and check this would have meant taxi to the opposite end of runway and be 15TH in line for takeoff after already waiting 30 mins. But I honestly felt we were in performance criteria anyway. Takeoff was uneventful but airborne I checked the data. The tailwind component came out to almost 11 KTS and our runway length performance with tailwind penalty was about 500 pounds below our actual weight. Lesson learned. Don't rush, don't assume, and don't be talked into pushing the limits just to make a schedule.

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Original NASA ASRS Text

Title: FLT CREW OF ACR LGT UNDER PRSSURE TO DEPART EWR JUST AFTER WIND SHIFT AND RWY CHANGE, MAKES THE WRONG ESTIMATES OF RWY LENGTH PERFORMANCE AND TAILWIND COMPONENT. FLT CREW DISCOVERS ERROR AFTER ACFT DEPARTED SAFELY.

Narrative: INCIDENT OCCURRED WHEN TWR DIRECTED A RWY CHANGE FOR DEPS. WE WERE NEXT FOR TKOF, TWR WAS RUSHING US TO ACCEPT A DIFFERENT RWY. WE CHKED PERFORMANCE DATA AND REPLIED WE WOULDN'T DO IT, TOO HEAVY. SO THEY SAID WE COULD DEPART ON ORIGINAL RWY IF WE COULD DO SO IMMEDIATELY. WE WERE 12000 LBS UNDER MAX RWY LIMIT WT. BUT NOW THE WINDS WERE 20 DEG OFF OUR TAIL AT 12 KTS. I USED A RULE OF THUMB AND FELT THAT EQUALED 10 KTS DIRECT TAILWIND, OUR MAX ALLOWABLE. ALSO, I FELT 12000 LBS CUSHION ON RWY LIMIT WT WAS MORE THAN SUFFICIENT TO COVER THE TAILWIND. TO DELAY AND CHK THIS WOULD HAVE MEANT TAXI TO THE OPPOSITE END OF RWY AND BE 15TH IN LINE FOR TKOF AFTER ALREADY WAITING 30 MINS. BUT I HONESTLY FELT WE WERE IN PERFORMANCE CRITERIA ANYWAY. TKOF WAS UNEVENTFUL BUT AIRBORNE I CHKED THE DATA. THE TAILWIND COMPONENT CAME OUT TO ALMOST 11 KTS AND OUR RWY LENGTH PERFORMANCE WITH TAILWIND PENALTY WAS ABOUT 500 LBS BELOW OUR ACTUAL WT. LESSON LEARNED. DON'T RUSH, DON'T ASSUME, AND DON'T BE TALKED INTO PUSHING THE LIMITS JUST TO MAKE A SCHEDULE.

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.