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steps, that is, major descents at
certain stages requiring large power
changes that can be a pain with an
engine out. It’s often a good idea to
keep a consistent glide path as much
as possible throughout a nonprecision
approach – the minimum
heights at each step are just that –
minimum heights. There’s nothing
to stop you being above them if you
64 Operational Flying
are descending under control (300
feet per mile gives you 3°).
On non-precision approaches, if
visual reference has not been
established by Minimum Descent
Height, you may fly level at that
height if your heading is within 15°
of the runway QDM, and you may
go down further if you can see
where you're going, if you can land
at normal touchdown speed. This,
unfortunately, raises the temptation
of a dirty dart for the runway if you
see it, without really being in a
position to cope with the situation—
you are in a high drag landing
configuration, and have been for
some time. There are no
performance figures for go-arounds
under those conditions.
If you can't see anything by your
estimated time of reaching the
threshold, you must go around.
After 2 successive overshoots you're
allowed no more attempts until a
significant improvement in the
weather is reported—the meaning of
'significant' is left to common sense,
but you can have a third go if you've
previously used an autopilot, or you
have an emergency.
You may abandon an instrument
approach in favour of a visual one if
you have the aerodrome
continuously in sight, you are below
all cloud, and conditions are equal to
or better than those for circling (bear
in mind, though, the minimum RVR
of 800m (1200 in Canada), even
when visual, which is to guard
against shallow fog reducing the
visibility in the final stages).
For destinations, forecasts must
indicate that the weather will be at or
above the minima for 1 hour either
side of ETA. For a non-precision or
circling approach, the ceiling must
also be at or above MDH.
Destination and En-Route Alternates
Should the weather deteriorate
below acceptable limits you must
consider diversion, but if things are
improving, you can request holding
at the optimum level for up to a half
of your holding allowance before
going elsewhere. If you eat into this,
you should have 2 alternates
available, with enough fuel to reach
one of them (a minimum of 60 nm
away) with 45 minutes' holding fuel
on arrival.
You can use an Isolated Aerodrome
procedure instead of alternate fuel
for destinations with no suitable
alternate, which means you must
carry significantly more fuel than
normal, that is, about 2 hours' worth
as opposed to 45 minutes. The
amount of the reserve is related to
statistical information about local
weather conditions, and is covered
more fully later.
Met reports and/or forecasts must
indicate that the weather at the
aerodrome will be at or above the
planning minima below for an hour
either side of ETA:
Approach Planning Minima
Cat II and III Cat I (RVR)
Cat I Non-Precision (RVR with ceiling at
or above MDH)
Non-
Precision
Non-Precision (RVR with ceiling at
or above MDH) plus 200 ft/1000 m
Circling Circling
DH/MDH
The starting point for Decision Height
is the Obstacle Clearance Height for the
landing aid, or Circling Minima as an
alternative (Circling Height should
be regarded as MDH/DH for any
Operational Procedures 65
instrument approach followed by
circling). Add 10 feet (sink
allowance) to that, plus the Pressure
Error Correction for the type, which
will be in the Flight Manual, so DH
= OCH + PEC + 10 feet. If the ILS
is offset, the DH must be at least the
height at the Middle Marker.
The OCH for non-precision
approaches should include a fudge
factor for sink and PEC, so you can
read OCH directly as the Minimum
Descent Height (MDH for nonprecision
approaches being the same
as DH for precision approaches), or
MDH = OCH. If you're a newbie,
that is, you have less than 50 hours
P1 on the relevant type, expect to
increase your DH or MDH by 100'.
Non-Precision Approaches
(Onshore)
The MDH for a non-precision
approach must be higher than the
OCH/OCL for the category of
aircraft, the system minimum (see
table below), or any State minima.
Approach Aid System Min
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