July 1, 2000
By John S. Yodice
Do you know the technical difference between ground visibility and flight visibility? It could be important. Suppose you are sitting in your aircraft on the ground at a satellite airport (an airport that is in the same surface airspace area as the primary airport on which the airspace designation is based). The primary airport is reporting less than one mile's ground visibility. The satellite airport does not have weather reporting, but you can see a mile or more in all directions. You see that the haze layer is not very thick. You would like to be able to depart special VFR, get on top of the haze, and proceed VFR to a destination that is reporting good VFR conditions. Can you legally obtain a "special VFR" clearance? There has been confusion about the answer to that question, and it has led to a regulatory change.
In this situation, the technical difference between ground and flight visibility becomes important. That's because in order to get a special VFR clearance from the ATC facility controlling the airspace, ground visibility at the departure airport must be at least one statute mile. If ground visibility is not reported at the airport, as in this situation, then flight visibility must be at least one statute mile.
This has been the problem. Until the regulatory change provided an explanation, technically a pilot on the ground could not determine flight visibility. Flight visibility is by definition determined by a pilot from the cockpit. The FAA interprets this definition to mean that flight visibility can only be determined when an aircraft is airborne.
Ground visibility, on the other hand, is an officially reported condition, not a pilot-observed condition. Ground visibility is defined to be "the prevailing horizontal visibility near the Earth's surface as reported by the United States Weather Service or an accredited observer." A pilot, unless he also happens to be an accredited weather observer, cannot report ground visibility.
So, unless there happens to be a pilot in flight who reports the flight visibility conditions—and who doesn't have to be an accredited observer—our pilot on the ground is stuck. ATC has been reluctant to issue a special VFR clearance when the visibility at the main airport was reported to be less than a mile. A regulatory change solves this situation, and in explaining it, gives us an opportunity to review the "special VFR" regulation.
Let's start with the basics (forgive the pun) of FAR 91.155 that all pilots know but like to be refreshed about from time to time. (There are additional requirements for student and recreational pilots.) Let's look particularly at the "basic" (as distinguished from "special") VFR weather minimums that apply _to VFR operations at an airport within controlled airspace. By that I mean an airport that has controlled airspace that begins at the surface of the airport. That's any airport within Class B, C, and D airspace. That's also any airport within Class E airspace that begins at the surface of the airport (not an airport that has Class G airspace at its surface with Class E airspace above). The basic VFR visibility minimums that apply in this airspace are at least three statute miles' ground visibility and at least three statute miles' flight visibility. In other words, a pilot may not operate an aircraft to or from such an airport under VFR with less than three miles' visibility, both ground and flight.
Also as part of the basic VFR requirements, if the ceiling reported at the airport is less than 1,000 feet, an aircraft may not be operated VFR beneath the ceiling.
For completeness we must mention that within this airspace the "basic" cloud clearance minimums also apply. Here they are: A pilot may not operate an aircraft at a distance from clouds that is less than 500 feet below, 1,000 feet above, and 2,000 feet horizontally. (Not relevant here, but remember that there are stricter minimums in controlled airspace above 10,000 feet msl.) There is one interesting exception to these cloud clearance requirements. In Class B airspace, which presumably has the highest density of traffic, an aircraft may be operated closer to clouds than these minimums. The minimum is "clear of clouds," the same minimum we see in some Class G uncontrolled airspace and in special VFR operations. It makes sense, if you think about it. All aircraft in Class B airspace are being provided separation service by ATC. And it would cause problems for the controllers if pilots refused radar vectors or routings because following them would result in less than the required cloud clearances.
Which brings us to the "special VFR" rules of FAR 91.157. We can get a break from the "basic" minimums if we first obtain a special VFR clearance from the ATC facility that has jurisdiction of the airspace. Then the "special" and not the "basic" VFR minimums apply. The special VFR weather minimums are one mile's flight visibility and clear of clouds. Under the special VFR rules, in addition to the flight visibility minimum, there also is a ground visibility minimum. An aircraft may not take off or land under special VFR unless ground visibility is at least one mile. If ground visibility is not reported, then flight visibility must be at least one statute mile.
Back to our pilot on the ground at the satellite airport. He can't take off because ground visibility is not reported at the satellite airport, and he can't make a flight visibility determination because he is not in flight. This is a dilemma that has now been resolved.
Since May 23, 2000, FAR 91.157 has been amended to expand the term flight visibility to include the visibility from the cockpit of an aircraft in takeoff position at a satellite airport that does not have weather reporting capabilities. This allows a pilot at such an airport to determine whether the visibility minimums exist for a special VFR departure. If the pilot on the ground determines that the visibility is one mile or more, special VFR is permissible.
The amendment makes it clear that a pilot's determination of flight visibility from the cockpit of an aircraft on the ground is only for the purpose of the special-VFR rule. All other flight visibility determinations must be made in flight. Similarly, it makes it clear that this visibility determination is not an official ground visibility report, since the pilot is not an official weather observer. The amendment also makes it clear that this change applies only to flights conducted under Part 91.
The rest of the rules governing special-VFR operations still apply.
For special VFR at night, the pilot must be rated and current for instrument flight, and the aircraft must be equipped for instrument flight. For this rule night (it's different for other rules) is considered to be the time between sunset and sunrise. (In Alaska, the "instrument" requirement applies when the sun is less than 6 degrees or more below the horizon.)
Helicopter operators get some additional benefits. A helicopter may be operated special VFR without the one-mile visibility minimum. And for special VFR at night, a helicopter pilot does not have to be instrument-rated, and the helicopter does not have to be equipped for IFR.
While a special VFR clearance may be obtained at most airports within controlled airspace, it is not permitted for fixed-wing aircraft at some 33 specifically identified airports; they are indicated on VFR charts and in aeronautical publications. As you would guess, they are the airports with the highest traffic density.
Our explanation of the technical difference between ground and flight visibility is important to pilots beyond this rule change. 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, and most often, the visibility minimum is flight visibility as observed by the pilot from the cockpit. For example, an aircraft transiting the controlled airspace, but not operating at the airport, must maintain flight visibility of at least three miles but is not bound by the officially reported ground visibility.
Safety and Education,
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Your CFII usually follows up route-planning drilling with a review of appropriate regulations, and today’s selection is 14 CFR 91.185, "IFR Operations: Two-way radio communications failure."
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