Sequencing with IFR
When sequencing VFR circuit traffic with IFR, you must ensure that you have an adequate gap in the inbound stream to accommodate the aircraft. As a general rule of thumb, you should have required vortex gap + 4 miles (If the required vortex spacing is 8 miles, this means you need a gap of at least 12 miles between IFR inbounds to safely accommodate the VFR traffic. This gap allows for the vortex and the significant catch up that there is likely to be. This gap can be reduced or increased, depending on aircraft performance. Aerodrome control should coordinate with approach control on where and how big the gaps need to be. When a circuit aircraft is ready to turn on base leg, they may not be number 1 to make an approach. If the delay is only going to be a couple of miles, they should be instructed to extend the downwind leg and passed information on the traffic they are following. The aircraft should then position itself behind the traffic - They may choose to position behind less or more than the required spacing. Monitor the situation, especially any further IFR traffic that is to arrive afterwards. If the delay could be several minutes, then the aircraft should be instructed to orbit at the end of the downwind leg and passed information on the traffic they are following. If you are unsure where the aircraft is going to fit into the sequence, they should be instructed to orbit and await further instructions.