Legal Briefing

The "see and avoid" rule, Part 91.113(b) of the federal aviation regulations (FARs), is backed up by many other regulations in the General Operating and Flight Rules of Part 91. All of these regulations stem from the same basic principle-in order to avoid another aircraft, you have to see it. FAR 91.113(b) states, "When weather conditions permit, regardless of whether an operation is conducted under instrument flight rules or visual flight rules, vigilance shall be maintained by each person operating an aircraft so as to see and avoid other aircraft." For now, let's focus on the aircraft operating under visual flight rules (VFR). FAR 91.155 sets forth the "Basic VFR weather minimums" that a pilot must have before conducting a flight under VFR.

Three weather phenomena must be considered in determining whether a flight may be conducted under VFR below 10,000 feet mean sea level: visibility, cloud clearance, and ceiling.

Visibility

In Classes B, C, D, and E airspace, a pilot needs a minimum of three statute miles' visibility to operate under VFR day or night. In Class G airspace, a pilot must have at least one statute mile visibility during the day and three statute miles at night. However, the rule allows an exception to the Class G night-visibility requirement if the visibility is at least one statute mile, the pilot stays in the airport traffic pattern within one-half mile of the runway, and remains clear of clouds.

A distinction between ground and flight visibility could affect whether a pilot may conduct the flight. Ground visibility is defined in FAR Part 1 as "the prevailing horizontal visibility near the earth's surface as reported by the United States National Weather Service or an accredited observer." If an airport within controlled airspace officially reports weather, a pilot taking off, landing, or entering the traffic pattern at that airport is bound by the official ground visibility. Otherwise, he may use "flight visibility," which is defined as the average forward visibility observed by the pilot from the cockpit. So, an aircraft transiting controlled airspace, but not operating at the airport, must maintain the proper flight visibility but is not bound by the reported ground visibility.

Cloud Clearances

In Class B airspace, day and night, a pilot must remain clear of clouds. In Classes C, D, and E airspace, day and night, the pilot must stay at least 500 feet below, 1,000 feet above, and 2,000 feet horizontally from any cloud. It is in Class G airspace that the cloud-clearance limits change, depending on how far above the surface you are and whether it is day or night. Below 1,200 feet above the surface, the pilot must remain clear of clouds during the day. At night, the minimum separation is 500 feet below, 1,000 feet above, and 2,000 feet horizontally. Above 1,200 feet agl (above ground level), day and night, the pilot must remain 500 feet below, 1,000 feet above, and 2,000 feet horizontally from any cloud.

Ceiling

The ceiling minimum applies only to airports in controlled airspace. The rule states that "no person may operate an aircraft beneath the ceiling under VFR within the lateral boundaries of controlled airspace designated to the surface for an airport when the ceiling is less than 1,000 feet." This restriction does not apply to flights in uncontrolled airspace. Note that an aircraft may operate VFR above a reported ceiling, "on top," even while passing right over the airport.

Student and recreational pilots are subject to additional restrictions listed in FAR Part 61. These pilots may not act as pilot in command without visual reference to the surface-no "on top" operations. To command a flight, they must have flight or surface visibility of at least three statute miles during the day or five statute miles at night. For recreational pilots, the nighttime restrictions apply from sunset to sunrise.

For flights above 10,000 feet msl (mean sea level), the limits for VFR flight are fairly standard. In Class E airspace, a pilot must have flight visibility of at least five statute miles and remain at least 1,000 feet below, 1,000 feet above, and one statute mile horizontally from any cloud. Similarly, in Class G airspace more than 1,200 feet above the surface, a pilot must have flight visibility of at least five statute miles and remain at least 1,000 feet below, 1,000 feet above, and one statute mile horizontally from any cloud.

It takes a lot of practice to be able to rattle off all of the different VFR cloud clearance, ceiling, and visibility limits. However, there is one set of minimums that you can remember that will keep you in compliance with FAR 91.155 for all airspace below 10,000 feet: visibility of at least three statute miles; cloud clearance of at least 500 feet below, 1,000 feet above, and 2,000 feet horizontally; and a ceiling of at least 1,000 feet above the surface.