Widebody Transport
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 0
Situational Awareness; Confusion; Human-Machine Interface
ATC Issue All Types; Ground Incursion Runway
Air Traffic Control Issued New Clearance; Air Traffic Control Separated Traffic; Flight Crew Requested ATC Assistance / Clarification; General Flight Cancelled / Delayed
Human Factors; Airport; ATC Equipment / Nav Facility / Buildings; Procedure
I was working Local Control. I had crossed 3 aircraft at an intersecting taxiway; expecting Ground Control to move them along quickly. For some reason; all three lingered on the taxiway for quite a while. I was trying to depart 2 aircraft from the full length of the runway; however the last of the 3 previously crossed aircraft appeared to be close to the runway on the Airport Surface Detection Equipment (ASDE); so I put Aircraft X in position so I could roll him as soon as the traffic moved. It seemed to be taking longer than usual for the Ground Controller to get the traffic on the taxiway moving; so I went over and asked the Ground Controller if they could at least ask the aircraft to move up as close as possible to each other so I could depart. He did; and the third aircraft that I had been worried about moved up and appeared to be well clear on the ASDE (couldn't quite tell out the window because it was dark; so I was relying on the ASDE). I cleared Aircraft X for takeoff; to which he responded that he didn't think the aircraft was clear of the runway. I told him the aircraft appeared to be clear on the ASDE and to let me know when he thought the aircraft had moved far enough away from the runway to depart. I apparently did not say 'cancel takeoff clearance'; however Aircraft X did not start rolling until after he told me the plane was clear enough for him to depart and I re-cleared him for takeoff.Maybe some sort of mark on the ASDE so you know a plane is fully clear of the runway when you can't quite see out the windows. The aircraft that I'd crossed that was supposedly in the way appeared to be at least 1 cm away from the runway on the ASDE when I cleared Aircraft X for takeoff; it's not like the plane was right on the line of light gray/dark gray where the runway meets the taxiway. There was quite a bit of space between the aircraft icon and the runway; so to me; it appeared there was plenty of space for the two to pass.
The Local Controller cleared an aircraft for takeoff. The crew of the aircraft told the Controller they would wait because it appeared a taxiing aircraft had not cleared the runway. The Controller's ASDE-X (Ground Radar) indicated the taxiing aircraft was clear of the runway.