A TRACK DEV ON THE GANDER THREE DEP CAUSED BY CONFUSION AS TO WHEN THE CHARTED HDG CAN BE CHANGED TO DIRECT TOWARD THE ASSIGNED FIX.

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I WAS THE PF IN THE L SEAT. AS WE WERE TAXIING OUT FOR DEPT; THE PNF RECEIVED THE CLRNC. THE CLRNC WAS CLRED TO IAH VIA GANDER THREE DEP; DIRECT TOPPS; AS FILED. I ASKED 'ARE WE CLRED DIRECT TOPPS OR VIA YQX3.' THE PNF ASKED GND AND WE WERE CLRED DIRECT TOPPS VIA THE YQX3 DEP. THE DEP READS TO CLB RWY HDG; OR AS ASSIGNED FOR VECTORS TO ASSIGNED RTE. AFTER TKOF; WITH GEAR AND FLAPS UP; I STARTED A TURN DIRECT TOPPS. WHEN THE PNF SWITCHED TO DEP CTL; THE CTLR ASKED 'WHAT IS YOUR HDG?' HE TOLD US WE WERE SUPPOSED TO FLY RWY HDG TO 5000 FT AND THEN DIRECT TOPPS. WE HAD STARTED THE TURN TO TOPPS AROUND 2000 FT AFTER DEP. I HAVE REREAD THE SID SEVERAL TIMES AND BASED ON THE CLRNC FROM CLRNC DELIVERY; I FEEL WE DID WHAT WE WERE TOLD. I DO NOT SEE ANYTHING ABOUT RWY HDG TO 5000 FT BEFORE ANY TURNS. THE DEP CTLR TOLD US THAT 2-3 ACFT MAKE THE SAME MISTAKE EVERY MONTH. I FEEL A NOTE SHOULD BE ADDED TO THE SID; DO NOT TURN UNTIL REACHING 5000 FT. THAT WOULD CLR UP ANY CONFUSION. THERE WERE NO OTHER ACFT IN THE AREA DURING THE DEP.