Narrative:

Airport was east traffic; a configuration used 3 to 5 times a year. I was conducting OJT on the local one position. We had been working for some time; had several departures and working on where the marks were to obtain standard separation. By this point in the session; the developmental was consistently hitting the 3; 4 and 5 mile marks. An A319 on a SID departure was cleared for take off runway xxl. When the A319 was 3/4 down the runway and airborne; a B757 on a different SID departure was cleared for take off on runway xxl [a different runway]. When the A319 was switched to departure; I did notice he seemed to be climbing out rather slowly. I kept this information in the back of my mind so I could watch the separation between the A319 and the B757 when the B757 would tag up. Just as the B757 got airborne; I heard the traffic manager call out that the B757 needed to call company. I turned to find the traffic manager and tell him that the B757 was airborne. I instructed the developmental to pass the message for the B757 to call company and to contact departure. I forgot to look at the spacing as I had planned. Unfortunately; the B757 climbed out more rapidly than expected; combined with the A319's slower than anticipated climb out resulted in a loss of separation. Try not to push the developmental too early in training and under abnormal circumstances. Evaluate plans for future 'outs;' such as coordinate a different heading; apply visual separation; etc. Do not allow distractions to keep me from my first priority of separating the aircraft!

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Original NASA ASRS Text

Title: Tower Controller providing OJT described a loss of separation between two subsequent departures during a rarely used traffic flow.

Narrative: Airport was East Traffic; a configuration used 3 to 5 times a year. I was conducting OJT on the Local One position. We had been working for some time; had several departures and working on where the marks were to obtain standard separation. By this point in the session; the developmental was consistently hitting the 3; 4 and 5 mile marks. An A319 on a SID departure was cleared for take off Runway XXL. When the A319 was 3/4 down the runway and airborne; a B757 on a different SID departure was cleared for take off on Runway XXL [a different runway]. When the A319 was switched to Departure; I did notice he seemed to be climbing out rather slowly. I kept this information in the back of my mind so I could watch the separation between the A319 and the B757 when the B757 would tag up. Just as the B757 got airborne; I heard the Traffic Manager call out that the B757 needed to call company. I turned to find the Traffic Manager and tell him that the B757 was airborne. I instructed the developmental to pass the message for the B757 to call company and to contact Departure. I forgot to look at the spacing as I had planned. Unfortunately; the B757 climbed out more rapidly than expected; combined with the A319's slower than anticipated climb out resulted in a loss of separation. Try not to push the developmental too early in training and under abnormal circumstances. Evaluate plans for future 'outs;' such as coordinate a different heading; apply visual separation; etc. Do not allow distractions to keep me from my first priority of separating the aircraft!

Data retrieved from NASA's ASRS site as of July 2013 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.