Narrative:

Aircraft X and aircraft Y both released by approach. Aircraft X launched 'runway heading' off runway 8R and climbing to 7000. Aircraft Y was launched after aircraft X had crossed departure threshold of runway 8R also runway heading and 7000. Aircraft Y increased speed such that he was overtaking aircraft X. Aircraft X had been switched to departure frequency. I called departure controller requesting a turn for aircraft Y and advising I could maintain visual separation in the turn. I was told to keep aircraft Y on runway heading and then I shipped him to departure.it is quite possible; due to the nature of traffic at publication; to never encounter this situation during training. Given that both aircraft perform similarly I thought I had provided adequate spacing. I was wrong. I would recommend a wedge of departure airspace 15-20 degrees to either side of runway heading to allow tower controllers to issue turns in for IFR departures should it be necessary to maintain spacing. Another recommendation would be to only release one IFR at a time; or some other similar measure to help ensure IFR separation is maintained with multiple IFR departures.

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Original NASA ASRS Text

Title: PUB Tower Controller reported of departing two similar type aircraft and the second aircraft over taking the first.

Narrative: Aircraft X and Aircraft Y both released by approach. Aircraft X launched 'Runway heading' off RWY 8R and climbing to 7000. Aircraft Y was launched after Aircraft X had crossed departure threshold of runway 8R also runway heading and 7000. Aircraft Y increased speed such that he was overtaking Aircraft X. Aircraft X had been switched to departure frequency. I called departure controller requesting a turn for Aircraft Y and advising I could maintain visual separation in the turn. I was told to keep Aircraft Y on runway heading and then I shipped him to departure.It is quite possible; due to the nature of traffic at PUB; to never encounter this situation during training. Given that both aircraft perform similarly I thought I had provided adequate spacing. I was wrong. I would recommend a wedge of departure airspace 15-20 degrees to either side of runway heading to allow tower controllers to issue turns in for IFR departures should it be necessary to maintain spacing. Another recommendation would be to only release one IFR at a time; or some other similar measure to help ensure IFR separation is maintained with multiple IFR departures.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.