As pilots learn early in training, sections 91.155 and 91.157 of the federal aviation regulations tell the minimum weather conditions required for a flight under visual flight rules. Last month I reviewed what I call the “standard” VFR weather minimums: 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. In all of our national airspace below 10,000 feet mean sea level (where most VFR flying happens), a pilot who complies with at least the “standard” minimums will be in automatic compliance.
This month I’ll discuss the more complicated, but generally less stringent, minimums that are available in some airspace for particular operations. We get to pick and choose, but only if we want to.
Probably the less stringent minimums of greatest importance to most pilots are the ones that apply in uncontrolled airspace—that is, Class G—below 10,000 feet msl. During the daytime, pilots may operate VFR in Class G airspace with as little as one mile visibility. The “standard” cloud clearance minimums still apply, but are lowered in operations at or below 1,200 feet above ground level to “clear of clouds.” At nighttime, regardless of altitude, the standard minimums for both visibility and cloud clearance apply—with one narrow exception for low-level nighttime operations at airports in uncontrolled airspace. Operating an airplane in the traffic pattern of an airport in uncontrolled airspace, even at night, the minimums are one mile visibility and clear of clouds. To have the advantage of these lower minimums at night, the airplane must operate at or below 1,200 feet agl and remain within one-half mile of the runway.
Reduced minimums also are available in special VFR operations. Ordinarily, within the lateral boundaries of the controlled airspace that begins at the surface of an airport, the standard VFR weather minimums apply. However, if a special VFR clearance is first obtained from the controlling ATC facility, the special VFR minimums apply. The special VFR weather minimums are quite a bit lower than standard—one statute mile visibility and clear of clouds for airplanes. For special VFR operations between the time of sunset and sunrise (loosely “night”), the pilot must be rated and current for instrument flight and the aircraft must be equipped for instrument flight. (In Alaska, the “instrument” requirement applies when the sun is 6 degrees or more below the horizon). While a special VFR clearance may be obtained at many airports, it is not permitted for fixed-wing aircraft at 33 airports, which are identified on visual charts and in aeronautical publications. They are the airports with the highest traffic density.
A lower minimum in Class B airspace at first seems strange. Class B airspace overlies our busiest air-carrier airports, yet the standard cloud clearance requirements are reduced to “clear of clouds.” Consider, however, that all traffic is provided separation service in Class B. The standard three-mile visibility minimum still applies.
Helicopters, in general, must comply with the standard VFR weather minimums. However, their flight characteristics allow less-stringent minimums at low altitudes in uncontrolled airspace, and under special VFR. Below 1,200 feet agl in Class G airspace or when operating under special VFR, a helicopter may be operated clear of clouds without a numerical visibility minimum so long as it is operated at a speed that allows the pilot to see any air traffic or obstruction in time to avoid a collision. For special VFR at night, helicopter pilots do not have to be instrument-rated, and the helicopter does not have to be equipped for IFR.
One set of minimums in FAR 91.155 is higher—that is, more stringent—than the standard minimums. Those minimums apply at and above 10,000 feet msl. In that airspace, flight visibility must be at least five statute miles and cloud clearance must be at least 1,000 feet below, 1,000 feet above, and one statute mile horizontally. These increased minimums have not proven troublesome to VFR pilots operating at the middle altitudes. There are unique situations in mountainous areas where it is possible to be operating at or below 1,200 feet agl and still be above 10,000 feet msl. In those circumstances, we can get the benefit of minimums less than the standard: daytime, one mile and clear of clouds; nighttime, three miles and standard cloud clearance, except lower for nighttime operations in a close-in traffic pattern of an airport, explained above. (Student, recreational, and sport pilots have additional weather restrictions placed on them by FAR Part 61.)
Complicated? Yes. But, happily, we get to pick and choose or stick with “standard.”
John S. Yodice is an aviation attorney, pilot, and longtime aircraft owner.