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against distance, so you can avoid
hard objects (obstacles), particularly
when you can't see them. As a result,
the charts will emphasise rates and
angles of climb very strongly (climb
requirements are established with
one engine working hard for a
specified time).
There are reasons for multiple
engines, of course. One is that you
get more power and can lift more,
but another is for safety – failure of
an engine should not affect the
continued safe operation of the
flight, or the other one, which is why
there are isolation arrangements in
the engine compartment. It follows,
therefore, that the less the weight of
the machine, the better it can fly
with less power. In fact, with
reference to the profiles above, you
may find different max all-up
weights for helipads and clear areas
(there is no definition of a "helipad"
for performance purposes – rather,
it's any area that isn't a clear area, or
one that allows operation inside your
chosen performance group).
The take-off and landing phases of
any flight are the most critical,
demanding the highest skills from
crews and placing the most strain on
the machine. Because of this, strict
regulations govern the information
used for 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
114 The Helicopter Pilot’s Handbook
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
obstacles and be able to either fly
away or land without damage to
people or property (and the
machine) if an engine fails.
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.
Helicopters are certified in one of
several groups. For example, JAR
classifications are 1, 2 and 3, which
are broadly equivalent to the UK
Groups A, A(Restricted) and B (see
the table below). It is important to
realise that these are different from
Airworthiness groups, which dictate
how well the airframe stands up to a
forced landing.
Passengers JAR Class UK AN(G)R
Over 19 1 A
9-19 2 A (Rest)*
Less than 9 3 B**
*Up to 15 passengers and 12,500 lbs
** Less than 6,000 lbs
JAR Class 1 (Group A) helicopters
require no forced landing provisions
if an engine fails. Class 2 machines
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
　
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本文鏈接地址：The Helicopter Pilot’s Handbook(76)