LGT FLC MAKES OVERWT TAILWIND TKOF ON SHORTER RWY.

Narrative

WE WERE FLYING AN LGT (WITH XXX ENGS) FROM EWR TO MSP WITH A FULL LOAD OF PAXS AND GOOD HEADWINDS. FUEL WAS CONSIDERATION. WE NEEDED ALL WE COULD GET TO BE COMFORTABLE WITH OR ALTERNATE. THE ACFT WAS FUELED TO MAX STRUCTURAL: 172500. ON A COOL WINTER DAY WITH LONG RWYS; IT DIDN'T SEEM LIKE IT WOULD BE A PROBLEM. THE ATIS ANNOUNCED DEPS ON RWY 22'S -- THERE WAS A SLIGHT TAILWIND COMPONENT -- THAT I DID NOT NOTICE. IF I HAD; WE COULD HAVE SEEN RIGHT AWAY THAT WE NEEDED TO USE RWY 4. WHEN WE GOT TO THE HOLD SHORT FOR 22R; I BRIEFED FOR TKOF; INCLUDING A FUEL DUMPING PLAN IN THE EVENT OF ENG FAILURE AFTER V1. THE CAPT QUESTIONED THIS; SAYING I WAS USURPING HIS AUTHORITY. IT DIDN'T SEEM LIKE THE APPROPRIATE TIME TO DISCUSS IT; BUT I WANTED TO ASSURE HIM I HAD NO DOUBT WHO WAS IN CHARGE. IN THE MIDDLE OF THIS EXCHANGE; TWR CLRED US FOR TKOF; ANNOUNCING A 10 KT WIND FROM THE NW -- ABOUT AN 8 KT TAILWIND COMPONENT. I THINK THERE WAS TFC ON FINAL; SO THERE WAS TIME PRESSURE AS WELL AS THIS DISCUSSION OF MY BRIEFING. THE SO HAD MANY YRS EXPERIENCE WITH OTHER CARRIERS; INSPIRING MORE CONFIDENCE THAN WE WOULD HAVE HAD IN ANY OTHER SO ON ONLY HIS SECOND TRIP WITH THE COMPANY. THE CAPT TURNED TO HIM AND ASKED IF WE WERE OK TO GO WITH A 10 KT TAILWIND. HE SAID YES. (THE REAL ANSWER WAS NO; AS ANY OF US COULD HAVE SEEN IF WE'D LOOKED AT THE PAPERWORK). WE WENT. WE WERE COMFORTABLY AIRBORNE BY THE END OF THE RWY; BUT WE WERE LOW. I AM SURE STOPPING FROM V1/VR WOULD HAVE BEEN IMPOSSIBLE. WE WERE OVERWT FOR THE RWY BY ABOUT 2000 POUNDS. OTHER FACTORS: WITHIN THE PAST YR THE COMPANY HAS COME OUT WITH A NEW COMPUTERIZED MAX GROSS WT DATA. THEY HAVE COME OUT WITH MANY PARTIAL EXPLANATIONS SINCE THEN; BUT I AM STILL CONFUSED ON SOME OF IT. MY ATTENTIVENESS TO ALL THE DATA WE GET HAS JUMPED MARKEDLY AS A RESULT OF THIS INCIDENT. THE COMBINATION OF SEVERAL SMALL FACTORS SET ME UP FOR A BIG MISTAKE: SMALL ENS; A RWY NOT REALLY AS LONG AS I THOUGHT IT WAS; A TAILWIND; A DISTR; PERCEIVED TIME PRESSURE; OVERCONFIDENCE IN AN INEXPERIENCED SO.