VFR vs IFR: Weather Minimums Explained
Every pilot learns about VFR and IFR, but the nuances of weather minimums, flight categories, and airspace requirements can trip you up if you're not careful.
Flight Categories
Aviation weather uses flight categories to describe conditions. This app uses the NATO METAR color code system:
| Category | Color | Ceiling | Visibility |
|---|---|---|---|
| RED | Red | < 200 ft | < 800m (0.5 SM) |
| AMBER | Amber | < 300 ft | < 1600m (1 SM) |
| YLO2 | Yellow 2 | < 500 ft | < 3700m (2.3 SM) |
| YLO1 | Yellow 1 | < 700 ft | < 5000m (3.1 SM) |
| GRN | Green | < 1500 ft | < 8000m (5 SM) |
| WHT | White | 1500-2500 ft | ≥ 5000m |
| BLU | Blue | ≥ 2500 ft | ≥ 8000m |
These categories control the color coding on weather maps, with RED being the most restrictive conditions and BLU representing excellent VFR conditions.
VFR Weather Minimums by Airspace
The basic VFR weather minimums vary by airspace class:
Class B (Busy terminal areas)
- Visibility: 3 SM
- Cloud clearance: Clear of clouds
- Requires ATC clearance to enter
Class C and D (Controlled airports)
- Visibility: 3 SM
- Cloud clearance: 500 ft below, 1,000 ft above, 2,000 ft horizontal
Class E (Controlled, above 1,200 ft AGL)
- Visibility: 3 SM
- Cloud clearance: 500 ft below, 1,000 ft above, 2,000 ft horizontal
Class G (Uncontrolled, day, below 1,200 ft AGL)
- Visibility: 1 SM
- Cloud clearance: Clear of clouds
These are the legal minimums — not the recommended ones. Most instructors advise significantly higher personal minimums, especially for newer pilots.
IFR Approach Minimums
When flying IFR, each instrument approach has published minimums:
- Decision Altitude (DA) — Used for precision approaches (ILS). If you don't see the runway at DA, you go missed.
- Minimum Descent Altitude (MDA) — Used for non-precision approaches (VOR, RNAV LNAV). You level off and look for the runway.
- Visibility — The minimum flight visibility required. An RVR of 2400 is common for ILS approaches.
The MVFR Trap
Marginal VFR is where most accidents happen. Conditions look flyable but can deteriorate quickly. Classic scenarios:
- Scud running — Flying under a low ceiling trying to maintain VFR. One lower cloud layer and you're in IMC.
- Reduced visibility — Haze that drops from 4 miles to 2 miles over a few minutes.
- Terrain interaction — MVFR conditions in flat terrain might be survivable; in mountainous terrain, they're far more dangerous.
Making the Right Call
- VFR pilots: If conditions are MVFR or worse, seriously consider canceling.
- IFR pilots: Check that conditions are at or above approach minimums at your destination and alternate.
- Everyone: Get a standard briefing and check both current conditions (METAR) and the forecast (TAF).
The weather doesn't care about your schedule. The runway will be there tomorrow.