Date: 201604
Local time of day: 1201-1800
Location: DFW.Tower, TX
Flight conditions: Marginal
Aircraft: A319
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Final Approach
Airspace: Class B DFW
ATC / advisory: Tower DFW
Second aircraft: Medium Transport
Reporter function: Local
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Situational Awareness
Second reporter function: Local
Anomaly: ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Provided Assistance
Contributing factors: Staffing; Procedure; Airspace Structure; Human Factors
Primary problem: Procedure

Narrative: Weather MVFR; low layer reported at 900 feet; I was getting arrivals in sight at approximately a 2 mile final. Visibility was excellent below the clouds. Aircraft Y was on final; approximately 10 miles out when I noticed that they were more than 100 knots faster than Aircraft X; but still separated by more than 5 miles (estimated). The Final Monitor Controller initiated coordination with me asking if we (the tower) had the two aircraft in sight and could provide visual separation. I replied that we could not see the second aircraft. Final Monitor took no further action.The Local Controller and I were discussing the situation when another controller plugged in to Local to relieve the Local Controller. Local controller commented something to the effect 'oh well; I'll just file an ATSAP. It is well known that the controller intends to retire [soon]. Prior to working Local Control; the controller had been working Ground Control and was engaged in a conversation with the Flight Data controller and Front Line Manager (FLM). After the controller was relieved and went downstairs; I reported the event to the FLM who; I believe; was monitoring the position via wireless headset although he was busy on the computer with something and had another controller at his desk so he may not have been fully aware of what was going on. Also; since he is monitoring the Local position and not the he would not have heard the coordination between the final monitor and me. In hindsight I wish that I had directly instructed the Local Controller to break out Aircraft Y rather than attempt to influence his actions by asking him if he had it. Sure; TRACON could have done a better job; but we had a chance to ensure safety too but we chose to let it go.The Local Controller should be referred to Professional Standards and if they are not able to resolve the attitude issue; this controller should be removed from ATC duties until he retires.Training should be developed at this facility that helps to put the emphasis back on safety and less on efficiency.Professional Standards training for the whole facility to re-instill a professional attitude that reflects the importance of our job.


Second narrative: Aircraft Y was on final approach while I was working. I heard final monitor key up and slow him up. I realized then that we probably would lose 2.5 miles spacing; but had seen other aircraft before his arrival on final and thought for sure I would see him. I was in a relief briefing at the time and during that time when we begun to lose the 2.5 miles of separation we could both see both aircraft out the window and let it continue. The previous aircraft got off of the runway fine prior to aircraft Y landing.The final needs to be monitored more closely by final monitor and not rely on local control getting visual at the last minute. Also I should not have tried to give the position to another controller before this issue was solved.


Synopsis: A Tower Local Controller observed the other Local Controller allow an aircraft to land with less than the required minimum separation from the preceding aircraft.