Medium Large Transport; Low Wing; 2 Turbojet Eng
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 7.0
Distraction; Situational Awareness
ATC Issue All Types; Conflict Airborne Conflict; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued New Clearance; Air Traffic Control Separated Traffic; Flight Crew Executed Go Around / Missed Approach
Airspace Structure; Human Factors; Procedure
Aircraft Y was unexpectedly slow on their approach; and Aircraft X; the following aircraft was unexpectedly fast. I issued a speed reduction to Aircraft X in what I believed was plenty of time to keep 2.5 miles by the threshold; however; I failed to consider that; being 12 miles from the airport; I am required to keep 3.0 miles spacing; as 2.5 miles is only legal at 10 DME. Apparently; during my speed reduction to Aircraft X; I used the words 'speed' and 'knots' the same sentence; which led to a side conversation between 2 supervisors and 2 controllers in my immediate area wherein they all agreed that such phraseology violates the 7110.65; that it generally leads pilots to believe we are incompetent at our jobs; and that such willful non-compliance to published rules is grounds for formal punishment; etc. I allowed this side conversation to distract me from my duty; and cancelled Aircraft Xs approach clearance later than I otherwise should have; at approx. 2.94 miles; 11 DME from the field. A more timely speed reduction to Aircraft X would have helped; as well as a more concerted effort on my part to remain diligent to my work and not allow side conversations to distract me.
A Controller allowed final approach spacing to decrease to 2.9 miles before breaking the second aircraft out for re-sequencing. Three miles spacing was required.