ATM Principles and Separation Standards
The core of the job
Separation is the heart of the exam. You must know the minimum separation in all three dimensions: lateral, longitudinal and vertical. Vertical separation between IFR aircraft above the transition altitude is normally 1000 ft where reduced vertical separation minimum (RVSM) applies, and 2000 ft outside RVSM airspace. Know the transition level/altitude concept and how altimeter settings are applied.
Longitudinal and lateral separation
Longitudinal separation can be time-based (e.g. 10 minutes for aircraft on the same track at the same level where no radar is available, or 15 minutes where a following aircraft is faster), distance-based using DME or radar, or level-based. Lateral separation uses geographical separation (aircraft over defined geographic lines) or track separation (e.g. aircraft on tracks that diverge by a specified angle). Radar separation is typically 5 NM in terminal and area environments, reduced to 3 NM within terminal areas where approved. Wake turbulence separation depends on aircraft weight categories (Super, Heavy, Medium, Light) and must be applied to arrivals and departures.
Traps and a rule of thumb
Traps: applying 3 NM where only 5 NM is approved; forgetting that separation must be established and maintained before an aircraft is cleared; confusing the transition altitude (fixed by altimeter setting) with the transition level (variable); and misapplying wake categories. Rule of thumb: always ask "what is the minimum here, and is it approved in this airspace?" If radar separation is being used, the controller must be able to identify the aircraft and maintain surveillance. A worked example: two aircraft at FL350 both RVSM-approved - 1000 ft vertical separation is valid; if one is not RVSM-approved, apply 2000 ft or exclude it from RVSM airspace.