Separation Standards and Control Techniques
The minima framework
Separation is either vertical, horizontal (lateral or longitudinal), or achieved by radar. Vertical minimum is normally 1000 ft below FL290 and 1000 ft above FL290 with RVSM approval (2000 ft without). Horizontal procedural separation relies on position reports, time, or distance; lateral separation uses geographical separation, VOR radials, NDB bearings, or track separation. Longitudinal separation uses time (e.g. 10 or 15 minutes) or distance (e.g. 10 NM DME) with defined conditions.
Radar separation
Radar separation minima depend on the surveillance system: typically 5 NM in terminal/approach environments and 10 NM (or more) in area control, with reduced minima (e.g. 3 NM) only where approved and displayed. Traps: confusing the minimum with the standard used, forgetting that wake turbulence separation may exceed radar minima, and forgetting that identity and position must be positively established before applying radar separation.
Wake turbulence
Categories are based on maximum certificated take-off mass (Super, Heavy, Medium, Light). Separation is applied behind a heavier aircraft, and questions often test the leader/follower logic - the heavier aircraft is the one ahead.
Rule of thumb
Apply the largest of the applicable minima: radar, procedural, and wake turbulence. Separation is never less than the greatest requirement.
Worked example
A Medium behind a Heavy on approach: radar minimum is 3 NM but wake separation requires more; the controller applies the wake value.