Air Traffic Control and Navigation
Airspace and separation first
Airspace class drives almost everything else in this domain. Class A begins at 18,000 ft MSL and is IFR only; Class B, C and D surround busy airports with specific entry and equipment requirements; Class E is controlled but permits VFR; Class G is uncontrolled. Know which class carries a clearance or equipment requirement before you start comparing numbers.
Separation: 1,000 ft vertically below FL290, with RVSM maintaining 1,000 ft between FL290 and FL410; radar minima are typically 3 NM in terminal areas and 5 NM en route. Non-radar uses time and altitude.
Clearances are literal. 'Descend and maintain' does not clear an approach; 'cleared ILS RWY 27' does not authorise descent below the decision altitude; 'line up and wait' is not a takeoff clearance.
Navigation
Separate true from magnetic. Converting true to magnetic, easterly variation is subtracted: east is least, west is best. MEA guarantees obstacle clearance (1,000 ft, or 2,000 ft in designated mountainous areas) plus navaid reception; MOCA guarantees 1,000 ft but only within 22 NM of a VOR; MORA is a 1,000-ft grid value. RNAV and RNP differ: RNP includes on-board performance monitoring and alerting, and RNP AR requires specific authorisation.
Worked example. True heading 090, variation 15E. Magnetic heading = 090 minus 15 = 075. If you are 3 NM off track after 60 NM, your tracking error is 3 degrees (1-in-60 rule), and you correct by 6 degrees to regain track over the next 60 NM.