IFR vs. VFR: The Regulatory Landscape
Key Part 91 IFR rules, airspace requirements, and altitude/approach criteria compared with VFR operations.
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Questions Covered in This Set
12 cards to master
Under 91.173, what two things are required to operate IFR in controlled airspace?
A filed IFR flight plan AND an ATC clearance — filing alone is not enough.
Which classes of airspace are 'controlled' for the IFR clearance requirement?
Class A, B, C, D, and E (Class G is uncontrolled, so no clearance is required there).
What is special about Class A airspace (18,000 ft MSL to FL600)?
It is always IFR — VFR operations are not permitted.
State the 91.167 IFR fuel requirement.
Enough fuel to fly to the destination, then to the most distant alternate, then 45 minutes at normal cruising speed.
What is the 1-2-3 rule for requiring an alternate?
From 1 hour before to 1 hour after ETA, the destination forecast must show at least a 2,000 ft ceiling and 3 SM visibility; if not (or no instrument approach exists), an alternate is required.
What are the standard alternate minimums under 91.169?
600-2 for a precision approach and 800-2 for a non-precision approach, unless the chart specifies otherwise.
What is the minimum IFR altitude under 91.177 absent a published minimum?
2,000 ft above the highest obstacle within 4 NM in designated mountainous terrain; 1,000 ft elsewhere.
How do IFR cruising altitudes work below 18,000 ft (91.179)?
Magnetic course 0–179° = odd thousands; 180–359° = even thousands. No added 500 ft as in VFR.
What three conditions must be met to descend below DA/MDA (91.175)?
Continuously in a position to land using normal maneuvers, flight visibility at or above the published minimum, and at least one required visual reference in sight.
Name several of the required visual references in 91.175.
Approach light system, runway, threshold, threshold markings/lights, REIL, VASI/PAPI, touchdown zone, or runway end identifier lights.
Why might you depart IFR from a non-towered airport without a clearance in hand?
The airport may lie in Class G, where no clearance is required — but you need a void time or release before entering Class E.
What is the basic trade-off between VFR and IFR?
VFR: pilot sees and avoids and stays clear of clouds. IFR: pilot accepts ATC clearance, routes, and altitudes, and the system provides separation and obstacle protection.
