glenn (05/12/82)
Yeah, the FAR's sure are fun to interpret, hah?!?
Following is the text from the relevant sections, and my interpretation
thereof:
91.107 Special VFR weather minimums
(a) Except as provided in 93.113 [irrelevant to this discussion]
when a person has received an appropriate ATC clearance, the special
weather minimums of this section instead of those contained in
91.105 [which is the section on "normal" VFR minima] apply to the
operation of an aircraft by that person in a control zone under VFR.
(b) No person may operate an aircraft in a control zone under VFR
except clear of clouds.
(c) No person may operate an aircraft (other than a helicopter) in a
control zone under VFR unless flight visibility is at least one
statue mile.
(d) No person may take off or land an aircraft (other than a
helicopter) at any airport in a control zone under VFR -
(1) Unless ground visibility at that airport is at least
one statue mile; or
(2) If ground visibility is not reported at that airport,
unless flight visibility during takeoff or landing is at
least one statue mile.
(e) [States you can't operate in a control zone when it's dark when
the above minima apply unless you are instrument rated and equipped.]
-----------------------------------
Commentary:
First, I am assuming the question is in regard to fixed-wing aircraft,
which eliminates all the horsehockey about 'copters.
To answer your questions specifically:
(1) First, if the weather is below 91.105 minima (1000 and 3, as you state)
you can't TAKE OFF or LAND at an airport within the CZ unless (d)(1) and (2)
above are satisfied, without an appropriate clearance from the agency who
controls that airspace (i.e. the CZ). BUT if you are 10000 feet, the
flight viz is 50 miles and you maintain the 91.105 cloud-clearance limits,
the control zone minima do not affect you and you DO NOT need to contact ATC
to traverse the CZ (assuming of course that the airport elevation is not
above 7000, in which case you are in the ATA (if the airport is controlled)
and you have to contact the appropriate controlling agency anyway.) This
interpretation is both completely consistent with the above language (albeit
it is not obvious until you read it a few times) and it makes sense: The
purpose of a CZ is to maintain controlled airspace *down to the ground* when
the weather is below basic VFR, at airports where sufficient IFR activity
warrants the prevention of scud-runners zooming thru approach/departure
airspace below applicable transition areas (the floors of which are
either 700 or 1200 feet.) For example, at an uncontrolled field WITHOUT a CZ,
(but with a published IAP) scud-busters can legally fly VFR below 700ft
with 1 mile/clear-of-cloud limitation right thru the approach path, because
it's UNCONTROLLED AIRSPACE. The CZ is designed to prevent this (except with
approval of ATC.) It is not intended to encroach on higher-level airspace.
(2) If a layer of fog renders ground viz one mile, and you are at 12000,
you do NOT have to get an SVFR clearance to traverse the control zone, because
you are not taking off or landing (which obviates (d) above), the flight
viz is greater than one mile (which satisfies (c) above) and you are
maintaining clearance from clouds in accordance with 91.105 (which satisfies
(b) above. (e) does not apply, because the other weather minima have been met.
(3) To try to add some "logic" to the CZ language: Providing positive
control (i.e. all aircraft landing/taking off in CZ are on a clearance)
allows VFR departures from a CZ under conditions which would normally prevent
it, but which are perfectly suitable to continue VFR outside the CZ. For
example, suppose the airport is under a relatively local broken 800 foot
ceiling, but viz is 50 miles. Under 91.105, tough cookies. Wait it out. But
under SVFR, you can get a clearance to takeoff and depart the CZ (usually
in a specific direction) and you can continue below 700 outside the CZ
as long as you maintain clear of clouds (assuming uncontrolled airspace
outside the CZ, which it usually is below 700ft, unless you're in a TCA or
something, then none of this applies anyway.) The same example applies to
a low-viz-but-no-ceiling situation, such as "X2GF" (sky obscured, viz 2,
ground fog) where 91.105 would have you waiting on the ground waiting to
get out, or flying around outside the ATA waiting for the fog to burn off.
SVFR solves this problem, and can be used to good advantage, provided
the pilot has the judgement to use it wisely and not as a license to go
scudrunning.
(4) Getting inconsistent answers from CFI's is no surprise. If you are
just beginning in aviation, be prepared for lots more of the same,
unfortunately. Many CFI's are really not very well versed in the regs or
in aerodynamics, though most I've had are pretty good teachers and mostly
competent pilots. The best source for obscure answers is your local GADO
or one of Richard Taylor's books, ("Fair Weather Flying" and "Instrument
Flying" are chock full of good stuff about airspace/regs.) He is a real
stickler about understanding the regs. The trick is to understand the
reason *behind* the regs, and then figure it out from there.
Hope this clears things up a little. Happy landings.
- Glenn Golden (...vax135!lime!glenn) (BTL Holmdel)