A B737-700 FLC PERFORMS A DOWNWIND INTXN TKOF WITH WINDS MOST LIKELY OVER THE LEGAL LIMIT WITH APCHING TSTM AND XRWY LNDG TFC AT MDW; IL.

Narrative

PRIOR TO PUSHBACK; THE CALCULATED PERFORMANCE DATA WAS VERIFIED BY BOTH PLTS FOR A RWY 31C DEP OUT OF MDW. AS WE APCHED THE HOLD SHORT; GND CTL BROADCAST THAT ALL DEPS WITH THE EXCEPTION OF OURS WERE ON GND HOLD DUE TO AN APCHING TSTM (OUR DEP HDG WAS AWAY FROM THE APCHING STORM). HOLDING ACFT BLOCKED THE ENTRANCE TO THE APCH END OF THE RWY; THEREFORE; TWR INSTRUCTED US TO TAXI AROUND TO TAKE THE RWY AT INTXN K. THERE WAS CONFUSION AS TO WHETHER TWR WANTED US TO ENTER THE RWY AT INTXN K TO BACK TAXI FOR FULL LENGTH OR TO TKOF FROM INTXN K; YET IT WAS NOT VERBALIZED WITH TWR; NOR BTWN THE CAPT AND I. TWR WAS BROADCASTING UPDATED WIND DATA THAT SEEMED TO BE CHANGING RAPIDLY DUE TO APCHING STORM. WE (THE CAPT AND I) BOTH VISUALLY CHKED WINDSOCKS TO VERIFY THE WIND AS THE DATA TWR WAS GIVING DIDN'T APPEAR TO BE ACCURATE. WE DETERMINED THAT THE WINDS WEREN'T AS STRONG AS TWR WAS CALLING THEM AND THAT WE WOULD BE OK. AS WE ENTERED THE RWY AT INTXN K; TWR CLRED US FOR TKOF; TO WHICH I REPLIED WE NEEDED A SHORT DELAY. (THE TIME WAS NEEDED TO COMPLETE THE TKOF CHKLIST; WHICH WAS INTERRUPTED ON THE TAXI OUT DUE TO TWR CONVERSATIONS AND THE WIND CHKS.) TWR REPLIED THAT XRWY TFC WAS ON A 4 MI FINAL (THIS VERIFIED IN MY MIND THAT TWR WANTED US TO EXPEDITE AND TO TAKE OFF FROM INTXN K VICE FULL LENGTH). WE MADE AN UNEVENTFUL TKOF AND DEP. BECAUSE OF THE RUSH; TKOF DATA WAS NOT UPDATED ON THE PERFORMANCE COMPUTER WITH THE NEW WIND DATA; NOR FOR AN INTXN TKOF. POST TKOF CALCULATIONS REVEALED A STOPPING MARGIN OF ONLY 323 FT; OBVIOUSLY LESS THAN OPTIMUM AND A SIGNIFICANT FACTOR TO KNOW IN THE CASE OF A REJECTED TKOF. ERRORS: NOT RECALCULATING THE TKOF DATA WITH NEW WIND INFO AND LESS THAN FULL RWY LENGTH. LETTING THE SITUATION DRIVE OUR ACTIONS AND NOT SAYING 'STOP' OR AT LEAST ADDRESSING QUESTIONABLE ITEMS. A HIGH SENSE OF URGENCY WAS BROUGHT ABOUT BY THE FOLLOWING FACTORS: APCHING TSTM NEAR THE DEP END OF RWY. CONGESTION ON THE GND -- NUMEROUS ACFT WAITING FOR DEP. MODIFIED INSTRUCTIONS FROM TWR. CHANGING WIND DATA FROM TWR. INCOMPLETE CHKLIST PRIOR TO TAKING RWY. XRWY TFC ON FINAL. SUPPLEMENTAL INFO FROM ACN 512109: THE TWR CALLED THE WINDS WHEN ANOTHER ACFT ASKED FOR A WIND CHK. SINCE WE WERE DOING THE CHKLIST; THE WINDS DIDN'T REGISTER. AS I TOOK THE ACTIVE; I ASKED FOR THE WINDS AND THEY WERE 160 DEGS AT 11 KTS GUSTING TO 16 KTS. I DISREGARDED THE GUST FACTOR IN MY DECISION MAKING. THE WINDS WERE CHANGING DIRECTION QUITE A BIT DUE TO TSTM. WIND SOCKS WERE CALM TO 1/2 FULL. WE PULLED ONTO THE RWY AT INTXN K AND TWR TOLD US WE WERE CLRED FOR TKOF WITH TFC ON 4 MI FINAL.