Citation X (C750)
Air Traffic Control Fully Certified
Situational Awareness
ATC Issue All Types
General None Reported / Taken
Human Factors
At the time of the event the weather was VFR with better visibility and ceilings on departure than arrival. Due to arrival visibility/ceilings we had no plan alpha. Aircraft were reporting the field in sight between 1;400 and 900 FT on the ILS. Departures were visible to us until 1;500 to 2;000 FT MSL. A B767 called ready to go at the end of Runway 13R when a Citation X was on a five mile final for the same runway. The Citation X was indicating 160 KTS; I decided there was plenty of room for the B767 to depart. The B767 was cleared for take off; and I included 'Citation X on five mile final' with the clearance. The B767 heavy took an abnormally long time taking the runway for departure. The Citation X reported the field in sight on approximately a two mile final. I notified him that the Heavy B767 was on the go; which he appeared to be. Sending the Citation around would have resulted in both aircraft being at the same place at the same time so I elected to allow the Citation X to land. When the Citation X crossed the threshold standard runway separation existed; 6;000 FT (at least) and airborne. I was relieved that the operation had worked out. I shipped the B767 to departure. When the Citation X exited the runway he said 'That was pretty close Tower'. Normally in bad weather we provide two miles increasing to three miles for arrivals/departures. At the time of this event we were able to use visual separation as we were able to keep our departures in sight long enough. The best solution to solve this problem would have been to tell the B767 Heavy to start his departure now; or cancel take off clearance. This would have either encouraged the B767 to stop dilly-dallying; or created a safe out. With the B767 Heavy in position but not rolling I could have then sent the Citation X around with no possible conflict to worry about. Having the B767 Heavy try to exit the runway wouldn't have been a timely enough solution; at the rate that they were moving. Another good practice would be to allow even more room for the Heavy jets to get going; previously I felt five miles was enough.
A Tower Controller described an unsafe event when a B767 was cleared for take off with Citation traffic on a five mile final. The reporter acknowledged questionable spacing judgement on his part.