ACR MLG EXCEEDED 250 KTS BELOW 10000' AND THUS HAD DIFFICULTY MAINTAINING VISUAL SEPARATION WITH OTHER DEP TRAFFIC.

Narrative

I WAS CLRED FOR TKOF FOLLOWING MLG Y ACFT BEFORE IT HAD ROTATED. I DELAYED TKOF UNTIL I WAS ASSURED THAT MLG Y WOULD BE TURNED AWAY AS MY CLRNC WAS TO MAINTAIN RWY HDG. I WAS HANDED OFF TO DEP IN TIME TO HEAR THE CTLR GIVE MLG Y A 280 DEG HDG. I WAS GIVEN A 260 DEG HDG AND I EXECUTED THE TURN QUICKLY SO AS TO NOT OVERRUN THE TFC WHICH WAS CLBING SLOWER. I WAS GIVEN AND ACCEPTED A CLRNC TO MAINTAIN VISUAL SEP WITH MLG Y DURING THE INITIAL CLBOUT. THE MLG Y WAS NEXT GIVEN A LEFT TURN TO 120 DEGS AND BEGAN TO COMPLY WITH THE CLRNC. IN ORDER TO MAINTAIN VISUAL WITH MLG Y I HAD TO REDUCE PWR AND LEVEL OFF WHILE THE CTLR ISSUED ME A LEFT TURN TO 110 DEGS. I EXECUTED THE TURN BUT REMAINED LEVEL AS I HAD LOST VISUAL WITH THE CLBING MLG Y AND I WAS NO LONGER COMPLYING WITH THE CLB CLRNC OF THE SID. THE ACFT I WAS FLYING IS AN ADVANCED MODEL OF MLG X AND SPD CTL UNDER 250 KTS BECAME A PROB W/O ABRUPT PWR CHANGES THAT OVERRODE THE AUTOTHROTTLE OPERATION. I WAS HAND FLYING AT THE TIME AND THE AUTOTHROTTLES WERE ENGAGED IN THE CLB MODE WHICH IS THE SOP. HOWEVER; I QUICKLY REALIZED THAT THE AUTOTHROTTLES DO NOT RESPOND FAST ENOUGH AND THEREFORE I DISCONNECTED THEM SO AS TO REDUCE TO 250 KTS BELOW 10000'. I EXPRESSED MY DISPLEASURE TO THE CTLR WITH THE DEP PROCS AND MAINTAINED LEVEL UNTIL I WAS ASSURED ADEQUATE SEP. I WAS CLRED TO CLB TO 17000' AND INFORMED THAT MLG Y WAS AT MY 6 O'CLOCK AND 10 MI. HAD I NOT LEVELED OFF AND FOLLOWED THE CTLR'S CLRNC I BELIEVE THAT SEP WOULD HAVE BECOME LESSENED TO THE POINT WHERE WE WOULD HAVE HAD TO FILE A NEAR MISS RPT. NIGHTTIME JUDGEMENT OF DISTANCE IS DIFFICULT; BUT I JUDGED MY DISTANCE TO BE 2 MI FROM THE MLG Y; 8 O'CLOCK WHEN HE WAS ISSUED THE LEFT TURN TO 120 DEGS. THE SPD SEEMED FASTER AND MY CLB RATE WAS FASTER. WHILE ON DIVERGING COURSES IT WAS NO PROB UNTIL THE MLG WAS TURNED INTO ME.