Any Unknown or Unlisted Aircraft Manufacturer
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 3
Distraction; Situational Awareness
ATC Issue All Types; Conflict Airborne Conflict; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy
General None Reported / Taken
Environment - Non Weather Related; Human Factors
I departed Aircraft X for takeoff. Once approved separation was anticipated I cleared Aircraft Y for takeoff. Once airborne I noticed the departures in a closer proximity than anticipated but I was providing visual separation. I verified that I had appropriate separation on the radar display. In my judgment speed and spacing was adequate and I switched both aircraft [to] departure. Not long after I was called by the Departure Controller that they needed more space between departures because I had less than three miles between Aircraft X and Aircraft Y. This is not typical of my best practices to ensure separation. A possible factor could be aircraft performance. I wasn't anticipating the trailing aircraft to be so much faster or the lead aircraft to under perform like it did. Both aircraft were similar types. Another factor could be that I had been medically decertified due to a COVID-19 exposure at the facility. I was not sick but I was only notified the day before this incident that my medical had been reinstated and that I was to report to work the next day. [It] was quite a surprise to me and didn't give me any time to mentally prepare to conduct air traffic duties after [several] weeks away from work.The only recommendation would be a more advanced notification of a return to air traffic duties after a long time off. It allows controllers to be more mentally prepared to preform safety related duties.
Tower Controller reported a loss of separation between two departures and cited aircraft performance differences as a possible contributing factor.