A B737 CAPT BECAME CONFUSED AS TO WHERE FULL LENGTH OF THE RWY BEGAN; BLAMING IT ON UNCLR CHARTS.

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RWY 24 BHM FULL LENGTH 10000 FT WAS REQUIRED FOR TKOF PERFORMANCE. THIS OPTION WAS SELECTED IN THE PERFORMANCE COMPUTER AND REDUCED PWR TKOF DATA WAS GENERATED. OUR TAXI REQUEST INCLUDED RWY 24 FULL LENGTH. WE WERE TOLD TO TAXI TO HOLD SHORT OF RWY 24 AT A6. UPON HOLDING SHORT; TWR INSTRUCTED US TO 'BACK TAXI INTO POS RWY 24 CLRED FOR TKOF.' THE CAPT TAXIED OUT ONTO RWY 24 BUT CONTINUED HIS L TURN DOWN THE RWY. I IMMEDIATELY QUESTIONED HIM AND SAID THAT WE NEEDED THE FULL LENGTH OF 10000 FT. HE THOUGHT THAT WE HAD THE FULL LENGTH FROM THAT POS. I TOLD HIM THAT WE NEEDED TO BACK TAXI ALL THE WAY BACK; NOT JUST THE SHORT DISTANCE FROM A6 TO THE DISPLACED THRESHOLD. IN ORDER TO CLR UP OUR DIFFERENT UNDERSTANDINGS; I ASKED TWR THE DISTANCE WE HAD. WHEN TWR RESPONDED; I REQUESTED TO TAXI OFF THE RWY AND BACK AROUND FOR THE FULL BACK TAXI. TWR HAD NO PROB WITH THIS. AT THIS POINT; THE THROTTLES HAD NOT BEEN ADVANCED FOR TKOF (A TKOF HAD NOT BEEN ATTEMPTED YET). THE SUBSEQUENT BACK TAXI AND TKOF WERE UNEVENTFUL. RECOMMENDATIONS INCLUDE THAT THE BHM ARPT DIAGRAM PAGE INCLUDE A STATEMENT REQUIRING A BACK TAXI PAST THE DISPLACED THRESHOLD FOR RWY 24 WHEN 10000 FT IS REQUIRED. SOMEONE CAN MISTAKENLY LOOK AT THE ARPT DIAGRAM PAGE AND ASSUME THAT 10000 FT EXISTS AFTER THE DISPLACED THRESHOLD. THE PERFORMANCE COMPUTER DOES HAVE A NOTE ON THE RWY SELECTION PAGE STATING 'FULL LENGTH 10000 FT ON REQUEST;' BUT WHAT INFO IS NOT VERY APPARENT WHEN LOOKING AT THE 'TKOF NUMBERS' PAGE (AS TYPICAL WITH THE CAPT CREW POS). THIS CAN BE A CRITICAL MISTAKE SINCE WE DID NOT HAVE THE PERFORMANCE AVAILABLE TO DEPART RWY 24 FROM A6.