ARTCC Controllers reported issuing a climb clearance to an aircraft then changing the plan resulting in ATC vectoring aircraft and another aircraft taking evasive action to avoid a collision.
Synopsis
ARTCC Controllers reported issuing a climb clearance to an aircraft then changing the plan resulting in ATC vectoring aircraft and another aircraft taking evasive action to avoid a collision.
Narrative
While training Person A on sector XX/XY Aircraft X checked in and asked for higher. Person A gave higher to Aircraft X then reevaluated and issued a restriction. Aircraft X then read back the restriction and added we'll try our best at XA:12 (and 10 seconds). I then interjected and verified whether they would do it or do their best. Aircraft X then replied with we are accepting and will notify if they can't make it. We then issued a vector to help the situation. Then when it became more apparent that Aircraft X would not make his restriction I stepped in with more aggressive vectors to ensure the planes would at least not have a midair collision while attempting to achieve lateral separation as well. Then Aircraft Y responded to a TCAS as Aircraft Y responded to the TCAS I descended Aircraft Z just in case Aircraft Y needed further decent. Loss of separation occurred at XA:16 (and 37 seconds) 4 minutes and 27 seconds by my count so the restriction should have been achieved and even if we change the restriction to when I verified it would have been 4 minutes and 21 seconds.If we were to do it again I would just have stopped the underperforming aircraft the moment; he gave an unsatisfactory readback to begin with.
Second reporter narrative
While training on sector XX/XY Aircraft X checked in and asked for higher. I gave higher to Aircraft X then reevaluated and issued a restriction. Aircraft X then read back the restriction and added we'll try our best at XA:12 (and 10 seconds). Person B then interjected and verified whether they would do it or do their best. Aircraft X then replied with we are accepting and will notify if they can't make it. We then issued a vector to help the situation. Then when it became more apparent that Aircraft X would not make his restriction Person B stepped in with more aggressive vectors to ensure the planes would at least not have a midair collision while attempting to achieve lateral separation as well. Then Aircraft Y responded to a TCAS as Aircraft Y responded to the TCAS Person B descended Aircraft Z just in case Aircraft Y needed further decent. Loss of separation occurred at XA:16 (and 37 seconds) 4 minutes and 27 seconds by my count so the restriction should have been achieved and even if we change the restriction to when Person B verified it would have been 4 minutes and 21 seconds.If I were to do it again; I would have stopped Aircraft X underneath Aircraft Z rather than climb them.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.