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which a missed approach must be
initiated during a precision approach if
the required visual reference to
continue the approach to land has
not been established.”
In other words, it’s the height at
which you must go around if you
can't see anything vaguely
resembling a runway or the approach
lights. It's where a decision must be
made whether to carry on towards
the runway or get the heck out.
A precision approach is an ILS, MLS or
PAR, typically where you have to
maintain a constant glidepath.
Minimum Descent Altitude (MDA)
MDA is "a specified altitude
referenced to sea level for a nonprecision
approach below which
descent must not be made until the
required visual reference to continue
the approach to land has been
established."
There's no real decision here – you
are just not allowed below that
height on a non-precision approach.
If you do gain visual reference, the
approach is essentially terminated to
carry on visually.
A non-precision approach is one that
only has azimuth guidance (that is,
only left or right, no up or down),
such as VOR or NDB, and possibly
74 Canadian Professional Pilot Studies
circling in some countries (e.g. the
USA). Refer to the Instruments
chapter for more about this.
Minimum Holding Altitude (MHA)
The lowest altitude that guarantees
signal coverage, communications
and obstacle clearance, so it's the
same sort of thing as the MEA.
Helicopters
To operate over built-up areas at
altitudes and distances less than
those in 602.14, or to conduct a
landing or take-off within the builtup
area of a city or town, a plan
must be submitted to Transport
Canada at least five working days in
advance, to include:
·  certification that the
municipality has been informed
·  purpose of the flights
·  dates, alternate dates and
proposed times
·  location
·  type of aircraft
·  altitudes and routes, on a map
·  hazard procedures &
precautions
·  contact name
Required Visual Reference
Any part of the runway or aids
associated with it (such as lights) that
allow you to judge your position and
speed relative to the normal flight
path. You should, therefore, be able
to see certain items at minimums, to
include the runway, its markings,
approach or centreline lights, VASIs,
etc. If you don't get the required
visual reference at the correct point
in an approach, you must go around.
Runway Visual Range
Not to be confused with the above
(which has the same initials), or used
for flight planning purposes, RVR is
the maximum horizontal distance
that can be seen from pilot's eye
level at a typical touchdown on the
centreline. It is measured
automatically by a transmissometer, and
there should be one at the start of
the runway (A) and one at mid-point
(B). The idea behind RVR is to
provide consistency in the reporting
of visibility where runways are
concerned.
RVR can be compared against
ground visibility as follows:
Ground Visibility RVR
1 mile 5,000 feet
¾ mile 4,000 feet
½ mile 2,600 feet
¼ mile 1,400 feet
Approach Ban - 602.129
Although RVR figures should only
be advisory (the landing is governed
by approach minima), when the
figures are below minima, an IFR
approach must be discontinued
unless you have passed the outer
marker (or equivalent) and are
descending to the runway, or you are
training and don’t intend to land
(and ATC have been informed), or
RVR figures are fluctuating above and
below the minima and visibility is at
least ¼ mile, or you are conducting
a CAT III approach (see below).
The approach, therefore, is governed
by RVR figures. For aeroplanes,
Air Law 75
RVR A must be over 1200 feet and
RVR B over 600 feet (1200 if only
one is measured). For helicopters,
RVR must be at least 1,200 feet.
CAT III - 602.120
A CAT III approach must not be
continued beyond the outer marker
(or equivalent) unless the RVR is at
or above the minimums in the CAP.
Operating Minima
There are weather conditions under
which you're not allowed to land,
attempt to land, or take off. A
minimum cloud base and visibility is
laid down, based on national
regulations, ATC, or hard objects
(obstacles), in that order. The
　
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