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calculating take-off or landing
performance. Of course, in the old
days (say during the war, or when
the trains ran on time), having
enough engines to lift the load was
all that mattered and no priority was
given to reserves of power and the
like. Now it's different, and you must
be able to keep your machine a
specified distance away from hard
objects (obstacles) and be able to
either fly away or land without
damage to people or property (and
the machine) in the event of an
engine failure.
It is your responsibility to decide
whether or not a safe takeoff (and
landing) can be made under the
prevailing conditions. This means, in
particular, that, although the
crosswind on a particular runway
may be within limits for your
aircraft, you can choose another one
if you are not happy.
Flight Planning 341
Performance requirements will be
worked out before a C of A is
issued, over a wide range of
conditions. They are subsequently
incorporated in the Flight Manual,
which forms part of the C of A.
Aircraft are certified in one of
several groups, the one in which it
operates depending on its
Certification, Max All-Up Weight
and the number of passengers it
carries. Within these limits you can
choose which group to operate in,
and come under the appropriate
WAT (Weight, Altitude and
Temperature) limitations; it may be
more acceptable commercially, for
example, to operate in a lesser group
if it enables you to take more
payload, and make more money – all
you might need is longer runways.
Individual machine performance will
vary due to such variables as the age
of the airframe and engines, the
standard of maintenance, or crew
skill and experience, without the
engines being adjusted for several
seconds after the initial failure. What
you can do on one day under a given
set of circumstances may well be
impossible another time.
Performance is therefore a set of
average values—particular machines
may be better or worse.
The original testing, of course, is
done with new aircraft and
experienced pilots, which are known
as unfactored. Fudge factors are
applied to unfactored figures to
produce net performance (and gross
performance when they're not), so
there is a margin if you have a tired
engine, or a new pilot.
Occasionally, performance data in a
flight manual will already be
factored, but you will have to check
the small print on the chart, in case
they surprise you. Figures and graphs
are based on Standard conditions
which allow for fixed reductions in
pressure and temperature with
height. As we all know, the real
world isn't like that, so these
assumptions may not always be true
and due allowance must therefore be
made for them (if your aircraft is
performing sluggishly, you may find
it's not the machine, but the
conditions it has to work under that
are at fault).
You must, (with one engine out)
clear all obstacles under the
departure track within a defined area
by a specified margin, without
relying on seeing and avoiding them.
All the relevant data will be in the
graphs, but some groups have no
information at all in some areas. For
instance, an aircraft may be assumed
to have all engines working until
above 200 feet, under which height
there is no data for landing or takeoff
(which is why the take-off
minima should not be below this,
because you must be visual to avoid
any obstacles should an engine fail).
Sometimes, there can be no specific
provision for engine failure at all.
High Performance aircraft are a
special case, because they tend to be
operated much closer to their limits,
which means more planning.
Category A helicopters must be able
to stay airborne and meet certain
climb requirements in case of an
engine failure. Category B
helicopters, on the other hand, are
not able to stay up and must make
an emergency landing. This
obviously covers single-engined
342 Canadian Professional Pilot Studies
machines, but the definition includes
some twins, too.
Keeping to the helicopter theme,
Category A take-off procedures
involve a vertical and backwards
liftoff to a predetermined height
before going forward, which is
known as the Critical Decision Point
(or CDP), and gives you a choice of
action if an emergency happens
(actually, ICAO now call it the
Takeoff Decision Point, or TDP).
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