E135 CREW DIVERTED TO THE DEP ARPT AFTER THE DISPATCHER SYS OPS CTLR AND THE CREW ERRED IN THE REQUIRED LNDG RWY LENGTH; AFTER AN EICAS SLAT FAIL CAUTION MESSAGE.

Narrative

SLAT FAILURE. ON APCH TO HOU; WHEN FLAPS 20 DEGS WAS SELECTED -- SLAT FAIL CAUTION MESSAGE WAS PRESENTED ON EICAS. A MISSED APCH WAS EXECUTED. CHKLIST WERE COMPLIED WITH. THE PROB WAS NOT SOLVED WITH PUBLISHED CHKLIST. LNDG DISTANCE WAS CALCULATED WITH CHART FROM PERFORMANCE MANUAL NOT THE PROPER SECTION OF MANUAL. THIS RESULTED IN A LNDG RWY REQUIREMENT OF 8000 FT. HOU RWYS WERE NOT SUFFICIENT FOR THIS OP. DISPATCH WAS ADVISED OF THE RWY REQUIREMENT CALCULATED BY THE CREW. THEY WERE QUESTIONED OF THIS FIGURE AND ASKED IF THEY AGREED WITH THE CALCULATION. THE DISPATCHER SAID THAT HE WANTED THE FLT TO GO TO DFW. HE CALCULATED OUR FUEL BURN TO BE 2300 LBS. ACTUAL BURN WAS AROUND 3000 LBS. DURING APCH TO DFW THE CTLRS WERE ADVISED THAT WE WERE MINIMUM FUEL. ACFT LANDED WITH APPROX 2300 LBS OF FUEL. WELL ABOVE 45 MINS RESERVE. IN HINDSIGHT; THE LNDG LENGTH SHOULD HAVE BEEN CALCULATED FROM THE PROPER SECTION OF MANUAL. CHIEF PLT AND I HAVE DISCUSSED THIS ERROR. HAD THE DISPATCHER AND MAINT CTL CAUGHT MY ERROR IN LENGTH CALCULATION; PERHAPS A LNDG AT HOU WOULD HAVE BEEN ACCOMPLISHED. AS IT WAS; DISPATCH REQUESTED MY DIVERSION TO DFW. GIVEN FUEL REQUIRED TO COMPLETE THIS FLT; CURRENT AND FORECAST WX CONDITIONS; THE FLT COULD BE AND WAS ACCOMPLISHED WITHOUT FURTHER INCIDENT. I AM AWARE OF THE PROPER LNDG LENGTH CHART AS IT APPLIES TO THIS CHKLIST. AGAIN; NO ACFT LIMITATIONS OR FARS WERE VIOLATED OR EVER IN QUESTION. DISPATCH/MAINT MADE THE DISCUSSION TO RETURN TO DFW.