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have a limited exposure (that is,
occupants and third parties must
remain uninjured), while Class 3
types have to make a forced landing.
Single-engined helicopters therefore
come under Class 3. In addition,
Class 2 ops must be done under
conditions that allow a safe forced
landing, in terms of weather, light
and terrain – those done from
elevated pads in non-hostile
conditions must be done by day
only, otherwise you must abide by
Class 1. Class 3 ops must be done in
sight of the surface, by day, with at
least a 600-foot ceiling. The
minimum visibility is 800m.
The screen height for JARs is 35
feet, for takeoff and landing. There
are no distance requirements.
Group A helicopters must (with one
engine out) clear all obstacles under
the departure track within a defined
area by a specified margin. In fact,
they should be able to climb (after
CDP) at 100 fpm to MSA with the
gear down (most unfavourable C of
G), then continue at 150 fpm to
MEA with One Engine Inoperative
(OEI). Naturally, if the remaining
working engine is not powerful
enough to lift the weight, the flight
will not continue, so, as with fixed
wing, there is a point during the
takeoff procedure at which, if an
emergency happens, you elect to
carry on or reject, called,
unsurprisingly, the Critical Decision
Point, or CDP, which is the only
point at which you have two choices.
Which group you belong to depends
on Certification, Max All-Up Weight
and the number of passengers
carried, although the JAR
classifications are based on the latter
(see below). However, it may be
more acceptable commercially to
operate in a lesser group if it enables
you to take more payload, and make
more money – all you might need is
longer takeoff runs or less obstacles.
In other words (just to reinforce the
point), the conditions under which
Techie Stuff 249
you operate determine how heavy
your aircraft can be and, as a result,
your payload. Over a whole trip, the
weight could be dictated by:
·  Maximum weight
·  WAT limits (see below)
·  Space available
·  Obstacles
·  The route
·  Hovering OGE
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 (as amended) 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 (JAR does not
make a distinction between the two,
except for a 1% margin for IFR).
Also, 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).
Profiles
A profile is a series of target steps to
be achieved on takeoff or landing,
designed to give you the best chance
in an emergency. For example, with
a TwinStar in a clear area, you would
go up to 6 feet, then nose forward to
10 feet and 30 knots, (CDP)
accelerate to 40 kts (VTOSS) up to 550
feet, level out and accelerate to 55
kts (VY):
In practice, with both engines
performing normally, you would
accelerate as quickly as possible
through CDP and climb away as you
would with a single – only if an
engine fails would you decelerate to
VTOSS, or Takeoff Safety Speed (the
equivalent to V2 in a plane, for the
best angle of climb, then adopt VY at
the prescribed height, for the best
　
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