I recently was doing ATC at YSSY (Sydney airport) as GRD and TWR. At the time I had a B738 departing from RWY 34R and an A320 who was flying around doing something. I proceeded to ask the A320 for their intentions but received a standby until it was North West of Sydney. This is when I ran into trouble, the B738 was right behind the A320 to the South East and was requesting departure to the West. At this time the A320 was doing small circles slightly North West of the B738 and I knew that the B738 would have to cross paths with the A320. At this point, I told the B738 standby then proceeded to request the A320 to change heading or at least an altitude change. This is when disaster struck! I realised that as ATC TWR I couldn’t ask them to change heading or altitude. This soon became a big problem and in the end, the B738 went within minimum separation limits of each other then the B738 changed frequency without requesting as they thought I couldn’t do my job effectively. So my problem is, did I just not find the request altitude or heading button or does TWR not have control over that which would be a big issue.
Thanks a lot, James L