There are two sets of rules for flying aircraft in the NAS. These include:

• A. VFR and IFR
• B. Visual and Instrument
• C. Day and Night
• D. IFR and VOR

Answer: (A)

Two sets of flight rules govern operations in the National Airspace System: Visual Flight Rules and Instrument Flight Rules. When weather and visibility allow a pilot to navigate by sight and maintain visual separation from obstacles and other aircraft, the flight is conducted under VFR, following weather minimums and cloud clearance and using outside references for navigation. If conditions are insufficient for visual navigation, or if the mission requires it, the flight switches to IFR, relying on instruments, following an IFR flight plan, and operating with ATC clearance to maintain separation. The other options don’t describe the rule sets used to govern NAS operations: Day and Night refer to time of operation, IFR and VOR pairs a rule set with a navigation aid, and Visual and Instrument are the same idea but the standard terms are VFR and IFR.