VFR / IFR Weather Minimums

Weather minimums in aviation define the legally permissible lowest ceiling and visibility values within which a flight may be conducted under a given set of rules, in a given class of airspace, at a given altitude and time of day. They are not advisory targets — they are hard regulatory floors. Operating below applicable weather minimums without the appropriate clearance is a violation of the Federal Aviation Regulations (FARs) in the United States and the Standardised European Rules of the Air (SERA) in EASA states, enforceable through certificate action, civil penalty, or criminal prosecution in severe cases.

For Visual Flight Rules (VFR) operations in the FAA system, the foundational regulation is 14 CFR §91.155, which establishes Basic VFR Weather Minimums by airspace class. Class A airspace (18,000 ft MSL and above) is IFR-only — VFR is not permitted. Class B (major terminal areas): 3 statute miles visibility, clear of clouds. Class C and D (radar and tower-controlled airports): 3 SM visibility, 500 ft below clouds, 1,000 ft above clouds, 2,000 ft horizontal from clouds. Class E below 10,000 ft MSL: 3 SM, 500 ft below, 1,000 ft above, 2,000 ft horizontal. Class E at or above 10,000 ft MSL: 5 SM, 1,000 ft below, 1,000 ft above, 1 SM horizontal. Class G below 1,200 ft AGL during the day: 1 SM visibility, clear of clouds. Class G below 1,200 ft AGL at night: 3 SM visibility with the standard 500/1,000/2,000 cloud clearances. The more restrictive night requirements reflect the loss of visual terrain reference that daylight provides, a factor that statistically drives higher CFIT rates in IMC-entry accidents.

Special VFR (SVFR), under 14 CFR §91.157 (EASA equivalent: SERA.5010), allows operations within Class B, C, D, and E surface areas in conditions below standard VFR minimums when issued an ATC clearance. SVFR minimums are 1 SM visibility and clear of clouds. Night SVFR requires the pilot to be instrument-rated and the aircraft to be IFR-equipped. SVFR is not permitted at airports listed in §91.157 Appendix D (high-density traffic airports including JFK, LAX, ORD, and others) without specific waivers.

For IFR operations, instrument approach minimums are governed by §91.175, which requires that a pilot have either the runway environment in sight or be at the published Decision Altitude/Height (DA/H) for precision approaches or Minimum Descent Altitude (MDA) for non-precision approaches before descending below those altitudes. DA/H and MDA values are published on instrument approach procedure charts and vary by approach type, navigation equipment, and aerodrome-specific obstruction environment: a Category I ILS typically publishes a 200 ft DA with ½ SM (1,800 RVR) visibility minimum; a VOR approach might publish an MDA of 700 ft HAA with 1 SM visibility.

Alternate airport IFR minimums under §91.169 apply when the destination airport's forecast weather at ETA ±1 hour shows a ceiling below 2,000 ft or visibility below 3 SM, triggering the requirement to file an alternate. The alternate airport itself must then meet published alternate minimums — typically 600 ft ceiling / 2 SM visibility for precision approach airports and 800 ft / 2 SM for non-precision approach airports under standard alternate criteria. Part 121 dispatch alternate weather minimums under §121.625 are expressed in similar terms but require compliance with published airline alternate minima in Operations Specifications. In EASA states, the equivalent requirements appear in EU-OPS / CAT.OP.MPA.185 and are now harmonized with ICAO standards through EASA Implementing Rules.

Flight schools routinely establish additional above-regulatory weather minimums — often called "school minima" or "dispatch minima" — for specific student categories. A typical policy might require a minimum 1,500 ft ceiling / 5 SM visibility for student solos (versus the 1,000/3 legal minimum), a 3,000 ft ceiling for solo cross-countries, and prohibition of solo flight in any precipitation. These school-imposed minimums do not appear in any regulation but are a best practice widely recommended by AOPA, NAFI, and FAA Safety Team guidance to provide a safety buffer for pilots building experience.

Weather minimums are one of the most operationally complex topics in flight school administration because they vary simultaneously along multiple dimensions: airspace class, altitude band, time of day, IFR vs VFR, student solo vs dual, and school-imposed minimums layered above all regulatory baselines. A student cross-country planned through three airspace classes to an airport with a published precision approach requires correctly applying §91.155 for the departure VFR legs, §91.169 for the alternate determination at the IFR destination, §91.175 for the approach execution, and potentially school minima throughout. The dispatch team and the instructor must track all of these simultaneously without a mistake that exposes the student — or the school — to legal and safety risk.

For instructor evaluations and checkrides, weather minimums are a recurring examination topic. FAA Airman Certification Standards for Private, Instrument, Commercial, and ATP certificates all include tasks requiring applicants to correctly state and apply weather minimums for various airspace classes and flight scenarios. An applicant who confuses Class D cloud clearance requirements with Class G, or who cannot correctly determine when a filing alternate is required under §91.169, will fail their practical test — making weather minimum fluency a critical training curriculum objective that must be confirmed completed before a student advances to each certificate or rating.

Aviatize's smart planning and booking module allows flight schools to encode their school-specific weather minima as booking validation rules — so that a solo booking for a student below the school's solo minimum ceiling requirement is flagged for dispatcher review before it is confirmed, not after the student arrives at the ramp. Schools can configure different minima tiers by student category (pre-solo, post-solo local, post-solo cross-country) and by aircraft type (VFR-only vs IFR-equipped), creating a fine-grained dispatch rulebook that mirrors the school's operations manual without requiring dispatchers to manually check each rule against current weather for every booking.

For compliance documentation, Aviatize's compliance and auditing module stores the weather conditions and school minimum thresholds at the time each booking was approved or declined. This creates a timestamped record that demonstrates to Part 141 auditors and EASA Part-ATO oversight authorities that dispatch decisions were made systematically against documented criteria — not ad hoc. When a student's training record shows a weather-related ground delay, Aviatize's logs capture the specific METAR values and applicable minimum thresholds that drove the decision, providing defensible documentation in any review of the school's standard of care.