Date: 201308
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Aircraft: B737-700
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Landing
Airspace: Class C ZZZ
ATC / advisory: Tower ZZZ
Second aircraft: B757 Undifferentiated or Other Model
Reporter organization: Government
Reporter function: Local
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Situational Awareness
Anomaly: ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
Result: General None Reported / Taken
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: A B737 checked in on a right base for a visual approach to Runway 21. East RADAR (ER) advised me that the B737 did not see the King Air. I told ER I would provide Visual. The B737 slowed and turned back in to the runway and the spacing was fine. Then a B757 checked in on a visual approach just over a mile in trail and about 600 FT above the B737. I could tell from the BRITE the sequence was getting messy; but I still could not believe the B757 turned it in that close behind the B737. I was not sure how this was going to work; and at that time I heard ER in my ear 'you can give the B757 a 360 if you need' and that was it. The B737 and the B757 were complaining on my frequency about the sequence. I cut in and told the B757 'you're following the B737 ahead; I'm sorry; I may have to have you make a 360.' The B757 said he was slowed all the way but he would see what he could do. It was clear the pilot was frustrated and did not want to go around or make a 360. As the B737 landed and rolled out I thought this was actually going to work so I cleared the B757 to land. The B737 turned right at Taxiway C 6;850 FT down the runway. He slowed down considerably after he turned but he was still taxiing off. Half of the B737 was off the runway but the tail was not clear when the B757 crossed the landing threshold. I thought it was going to work; it was so close. The B737 was completely clear while the B757 was still within the first 1;000 FT of the runway. The sequence was a mess; the pilots were frustrated; and it was so close. This one was tough; but 'so close' is not the same as having approved separation. I should have canceled landing clearance and gave the B757 a go around when I was not positive it was going to work. The AIM 4-3-20 b. says the aircraft is clear when all parts of the aircraft are clear of the runway edge. Not when 'most' of the aircraft is clear. I also should not let it get personal. I wanted it to work because I thought the aircraft had received bad service; I knew they were upset; and I did not want anyone to have to go around or make a 360; making it even worse. Especially when they were as far apart on the runway as they were in the air. It did not feel unsafe. But; letting it go so far was the wrong call; I let myself get lead down a path. I cannot do that; even if it means someone has to go around.




Synopsis: Tower Controller described a separation loss with two successive arrival aircraft; the first not clearing the runway prior to second crossing the runway threshold.