Air Traffic Control, Navigation, and Airspace
The ATC Structure
Control flows through ARTCC (Center) for en route, TRACON for terminal airspace, tower for the surface, and FSS for flight planning and weather services. Know the clearance language: "cleared to descend" is an altitude clearance, while "cleared for the approach" authorizes the approach procedure but not a descent below any published segment altitude until established. A flight plan filed in the air through FSS is void if not airborne before the void time.
Airspace and Separation
Class A begins at 18,000 ft MSL and is IFR only. Class B/C/D surround busy airports; Class E floors are commonly 700 or 1,200 ft AGL; Class G is uncontrolled. Special use airspace (prohibited, restricted, warning, MOA, alert areas) and Military Training Routes must be checked against the route. RVSM applies from FL290 through FL410 with 1,000-ft separation; oceanic (NAT HLA) operations use prescribed tracks and position reporting.
Navigation
VOR/TACAN, NDB, and GNSS/RNAV; RNP/ANP monitoring; approach categories based on Vref speeds; minima expressed as DA (precision/APV) versus MDA (non-precision). Alternate minimums are published separately and are frequently the trap in planning questions.
Worked Example - 1-in-60 Rule
You are 10 NM left of track after 60 NM flown: correct by roughly 10° toward track. After 120 NM, 10 NM of error means only about 5°. The rule (degrees = 60 × offset ÷ distance) also works for wind drift estimates en route.