Federal Aviation Regulations 91.155 and 91.157 tell us the minimum weather conditions required for a flight under visual flight rules (VFR). These rules are fundamental to the primary way pilots avoid collisions—the see-and-avoid concept—using that indispensable piece of equipment, the eyeball. These weather minimums, along with other supplementary rules and procedures (for example, cruising altitudes, speed limits, right-of-way rules, and flight following), are designed to help give a vigilant pilot an opportunity to visually detect and avoid other aircraft in flight. Otherwise, if these VFR minimums are not met, the flight must be conducted under the instrument flight rules (IFR), or not at all.
Despite the complexity of these rules, for most VFR flying below 10,000 feet msl, there is a shortcut to learning and remembering the minimums. A pilot can memorize a relatively simple set of “standard” weather minimums. Then if a pilot observes these standard minimums, he or she automatically will be in compliance with FAR 91.155. (FAR Part 61 places a couple of additional weather restrictions on student, recreational, and sport pilots.) I should caution you that the word “standard” is my word that I coined to try to simplify the rules; it is not a word that appears in the regulations. It should not be confused with the words “basic” and “special,” which are terms that do appear in the rules and which have technical regulatory meaning.
Standard VFR weather minimums are what I will cover in this column. Next month, I will cover the VFR weather minimums that are different from “standard,” the ones that account for the complexity. In only one case are the minimums more stringent, when in the airspace above 10,000 feet msl. However, there are several instances where the minimums are less stringent. The benefit of this method of separating standard from the other VFR minimums is that a pilot can pick and choose among the technicalities of the other-than-standard minimums to take advantage of one or more of the lower (that is, less stringent) weather minimums that could give more flexibility to his or her flying. If the pilot doesn’t want or need the less stringent minimums, the pilot can use the more simple standard ones.
The standard VFR weather minimums relate to three weather phenomena that are familiar to pilots: visibility, cloud clearance, and ceiling. Here is what you need to memorize: The standard visibility minimum is three statute miles; the standard minimum distance from clouds is 500 feet below, 1,000 feet above, and 2,000 feet horizontally; the standard ceiling is at least 1,000 feet above the surface.
In addition, here are some important definitions:
Visibility. There is a distinction between ground and flight visibility. Ground visibility is by definition officially reported ground visibility—“reported by the United States National Weather Service or an accredited observer.” Where an airport in controlled airspace officially reports the weather, a pilot operating an aircraft at that airport (taking off, landing, or entering the traffic pattern) is bound by the reported ground visibility. Otherwise, the controlling visibility minimum is flight visibility as observed by the pilot from the cockpit, a very subjective observation. A good example is an aircraft transiting the controlled airspace of an airport, but not operating at the airport. The pilot is required to maintain flight visibility of at least three miles but is not bound by the officially reported ground visibility at the airport.
Ceiling. The ceiling minimum applies only to airports in controlled airspace, meaning controlled airspace down to the surface. The ceiling minimum does not apply to the many airports in Class G (uncontrolled) airspace. Pilots sometimes misinterpret the visual charts where an airport is underneath, but not within controlled airspace. The ceiling minimum does not apply to airports underlying controlled airspace (that is, where the controlled airspace does not go down to the surface). An aircraft may not operate VFR beneath a reported ceiling when the ceiling is less than 1,000 feet. An aircraft may be operated VFR above a reported ceiling—“on top,” as we say—even right over the airport. This is different for student, recreational, and sport pilots; they may not operate without visual reference to the surface.
A simple way to be in automatic compliance with the VFR weather minimums in any airspace below 10,000 feet is to observe the standard weather minimums of three miles visibility; cloud clearance of 500 feet below, 1,000 feet above, and 2,000 feet horizontally; and a ceiling of at least 1,000 feet.