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you can see them.
The official definition of a flight
under VFR is "one conducted under
Visual Flight Rules", conveniently
leaving out the bit that tells you what
the Rules are.
The Visual Flight Rules govern flight
in Visual Meteorological Conditions
(VMC). When the weather gets so
bad that you can't see where you are
going, Instrument Meteorological
Conditions (IMC) apply, and you must
fly under Instrument Flight Rules (IFR),
discussed below. The definition of
IMC is actually a negative one, being
"weather precluding flight in
compliance with Visual Flight
Rules". The point at which this
happens depends on the type of
airspace you are in.
Controlled Airspace - 602.114
You must have visual reference with
the surface with at least three miles
visibility, and be at least 500 feet
vertically and 1 mile horizontally
from cloud. In addition, inside a
control zone, ground visibility must
not be less than three miles, and you
should not be below 500 feet AGL,
except when taking off or landing.
Uncontrolled Airspace - 602.115
At or above 1,000 feet AGL
You must have at least 1 mile
visibility by day, 3 miles at night, and
be 500 feet vertically and 2,000 feet
horizontally from cloud.
Below 1,000 feet AGL
Aeroplanes
At least 2 miles visibility by day
(unless under an AOC), 3 miles
at night, and clear of cloud.
Helicopters
At least one mile visibility by
day (unless authorised by an
AOC or flight training
certificate), three miles at night,
and clear of cloud.
Air Law 213
Airspace Grd
vis
Horiz
cloud
Vert
cld
Ht
Control
Zone
3m 1m 500' 500'
Other
Controlled
3m 1m 500' n/a
Uncontrolled
above
1,000'
1m 2000' 500' n/a
Uncontrolled
below 1,000'
1m Clear of
cloud
Clear
cloud
n/a
VFR Over-the-Top - 602.116
This is flying over the top of a solid
bank of cloud, where you can't see
the ground, but you can see where
you're going.
You can only do it in the cruise by day
if you are at least 1,000 feet vertically
from cloud, or have a vertical
distance between layers of at least
5,000 feet, with at least 5 miles
visibility and the weather at the
destination is forecast for scattered
cloud or clear and visibility of at least
5 miles with no precipitation, fog,
thunderstorms or blowing snow
from 1 hour before to 2 hours after
ETA if you rely on a TAF.
Otherwise, the after ETA time
increases to 3 hrs.
Special VFR Flight - 602.117
This is used when you can’t comply
with IFR in a control zone – at
night, it is only used for landing at
the destination. It's a legal
technicality, used to allow VFR
aircraft to fly in an area where the
law says only IFR aircraft may fly.
The visibility must be at least ½
mile for helicopters, and 1 mile for
everything else. You must also be
clear of cloud and able to maintain
visual reference with the surface, and
obtain clearance from ATC before
doing so, which means you must
have radios. Helicopters must also
fly slowly enough to avoid collisions
with other traffic or obstacles.
On your request (it is never
volunteered), permission will be
granted if traffic permits.
It may be authorised by a non-radar
equipped control tower and an FSS,
but remember that Special VFR only
applies in a control zone - although you
might be able to get to the edge of a
zone under it, you might not be able
to go further because the ½ mile
limit (for helicopters, anyway) may
increase to 1 mile outside the zone if
you cannot comply with low
visibility requirements.
IFR
Generally, all flights in IMC must be
conducted under IFR, although you
can actually fly under IFR at any
time, even if the weather is clear –
the essential difference between IFR
and VFR is that tighter margins are
applied for avoiding obstacles and
choosing your altitude according to
the direction you are flying in (the
Quadrantal Rule – see Cruising
Altitudes). In Class A, B, C, D, E or F
Special Use Advisory airspace, you
must also have ATC clearance, and
observe any conditions it includes.
IFR clearances must be read back,
except where a SID is in force and
you got the clearance on the ground
before departure, or you got it by
electronic means. However, ATC
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