Pilot Counsel

VFR weather minimums, part I

November 1, 2005

AOPA General Counsel John S. Yodice flies his Cessna 310 for business and pleasure.

It has been some time since we last reviewed the rules that tell us the minimum weather conditions for a flight under the visual flight rules (VFR). These minimums are set out in federal aviation regulations 91.155 and 91.157, a set of rules that you probably have found is not so easy to read and understand, much less remember in detail. Yet, 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. So let's review and try to explain them as simply as we can.

Despite the complexity of these rules there is a shortcut to learning and remembering the minimums for most VFR flight below 10,000 feet msl. A pilot can memorize a relatively simple set of "standard" weather minimums. Then if a pilot observes these standard minimums, he or she will automatically 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.

We will cover the "standard" VFR weather minimums in part I. In part II, next month, we will cover the VFR weather minimums that are different from "standard," the ones that account for the complexity. In one case the nonstandard minimums are more stringent. That case is the airspace at and above 10,000 feet msl. It's important to notice that there are also several cases in which the minimums are less stringent, giving us more flexibility for our VFR flying. 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 standard ones. Even for the pilot who wants to master the detail of all the minimums, for a test or other purpose, this method of explaining the rules should make it easier.

The standard weather minimums

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.

Memorize and observe these and you will be in automatic compliance in all of the airspace below 10,000 feet msl.

In applying these standard minimums, here are some important definitions and practical aspects.

Visibility. There is a distinction between ground and flight visibility. Understanding that distinction could afford a pilot additional flexibility. Ground visibility is by definition officially reported visibility on the ground — "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 is bound by the reported ground visibility. By operating at the airport, I mean taking off, landing, or entering the traffic pattern. By controlled airspace, I mean class B, C, D, or E airspace designated for the airport. Otherwise, and most often, the 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. In that case 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. Here is another important practical aspect. The ceiling minimum does not apply at all airports. It applies only to airports in controlled airspace, meaning controlled airspace down to the surface. That means the airports in class B, C, D, and some Class E airspace. The ceiling minimum does not apply to the many airports in Class G (i.e., uncontrolled) airspace. Pilots sometimes misinterpret charts where an airport is underneath but not in controlled airspace. A quick glance at the chart could make it seem that the airport is in controlled airspace. The ceiling minimum does not apply to airports underlying Class E airspace (that is, where the Class E airspace does not go down to the surface).

Also note that the rule is that 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. It is different for student, recreational, and sport pilots. They may not operate without visual reference to the surface.

So, to recap, 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. However, we can find some added flexibility for our VFR flying by reviewing, next month, the VFR weather minimums that are different from standard.

John S. Yodice