BA4100 ACFT ON TKOF ROLL; FLC RECOGNIZED INADEQUATE FIELD LENGTH FOR POTENTIAL ABORT. UPON CHKING THEY REALIZED THE ACFT WAS OVERWT FOR TKOF DUE TO PREVAILING TEMP; TAILWIND AND A ROLLING TKOF WHICH ALL CONTRIBUTED TO WT RESTRS.

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WE DEPARTED RWY 3 AT WASHINGTON NATL ARPT. OUR TKOF WT WAS 23900 LBS; CLOSE TO THE MAX TKOF WT OF 24000 LBS. DURING THE TKOF ROLL BOTH OF US WERE CONCERNED THAT ALTHOUGH ACCELERATION WAS NORMAL; THE END OF THE SHORT RWY WAS RAPIDLY APCHING AND WE WERE NOT AT ROTATION SPD. AS WE NEARED VR (WHICH FOR US IS EQUAL TO V1) IT BECAME OBVIOUS THAT ALTHOUGH WE WOULD TKOF IN THE REMAINING DISTANCE; IF WE HAD TO ABORT THE TKOF BEFORE V1 WE WOULD NOT BE ABLE TO STOP ON THE RWY. THE CAPT; WHO WAS FLYING REMARKED 'THERE'S NO WAY THIS IS BALANCED FIELD LENGTH.' AS WE CLBED OUT I REALIZED WE HAD PROBABLY BEEN WT LIMITED DUE TO THE RWY LENGTH BUT HAD NEGLECTED TO CHK THE PERFORMANCE DATA. AFTER REACHING CRUISE ALT I PULLED OUT THE PERFORMANCE CHARTS FOR DCA AND FOUND THE FOLLOWING: 1) THE MAX WT FOR RWY 3 AT THE PREVAILING TEMP WAS 22900 LBS. WE TOOK OFF AT 23900 LBS. 2) WE HAD MADE A ROLLING TKOF WHICH IMPOSES A PENALTY OF 1400 LBS. WE DID NOT ACCOUNT FOR THIS. 3) TKOF WITH A TAILWIND IS NOT AUTH. THE ATIS WIND WAS 260 DEGS AT 8 KTS WHICH MEANT WE HAD TAKEN OFF WITH A TAILWIND OF 6 KTS. 4) THE RWY WAS WET (IT WAS RAINING). ALTHOUGH SPECIFIC DATA ARE NOT PUBLISHED FOR CONTAMINATED RWYS; THE WET RWY WOULD CERTAINLY INCREASE THE DISTANCE REQUIRED TO STOP THE AIRPLANE IN THE EVENT OF AN ABORTED TKOF. IN SUMMARY; WE HAD TAKEN OFF 2400 LBS OVERWT (WHICH IS 10% OF MAX TKOF WT) WITH A 6 KT TAILWIND (WHEN NO TAILWIND IS AUTH) ON A CONTAMINATED SHORT RWY. WE WERE FORTUNATE WE DID NOT GET A WARNING LIGHT OR OTHER ANOMALY DURING THE TKOF ROLL; FOR IN THE LATTER PART OF THE TKOF ROLL WE WOULD NOT HAVE BEEN ABLE TO STOP ON THE RWY. RWY 3 HAS NO OVERRUN AND THE DEP END OF THE RWY IS ADJACENT TO THE POTOMAC! IN ANALYZING WHY WE HAD OVERLOOKED CHKING THE RWY WT LIMIT; WE IDENTED THE FOLLOWING CONTRIBUTING FACTORS: THAT PARTICULAR DAY WAS USUALLY WARM (13 DEGS C). IN THE LAST FEW MONTHS IT HAS GENERALLY BEEN MUCH COLDER AND CHKING THE PERFORMANCE CHARTS USUALLY YIELDED NO WT RESTRS. DURING OUR ARR AT DCA 2 HRS BEFORE DEP WE HAD LANDED ON RWY 18 WITH A HEADWIND (170 DEGS AT 8 KTS). WE OBVIOUSLY DID NOT PAY SUFFICIENT ATTN TO THE DEP ATIS WIND AND RWY INFO AND ALLOWED OURSELVES TO REMAIN IN A 'HEADWIND' MINDSET. IT WAS THE LAST LEG OF A 2-DAY TRIP AND ALTHOUGH WE WERE NOT CONSCIOUSLY RUSHING; THE FACT THAT WE WERE 'GOING HOME' MAY HAVE PLAYED A ROLE IN CAUSING THE LAPSE. THE INVALUABLE LESSON WE LEARNED THAT DAY IS THAT AS PER THE REGS; PERFORMANCE LIMITATIONS MUST BE CHKED PRIOR TO EVERY TKOF.