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NOT attempt to unfeather the
engine but land as soon as possible.
Techie Stuff 247
Failure of Feathering System
Most feathering systems don't
function below a certain low RPM
(typically 700-1000), so you don't
start with the blades feathered.
However, there are further
implications—if your engine fails
through a major mechanical fault,
you may not be able to catch the
propeller quickly enough. The usual
reaction is to close the throttle of the
dead engine first, so opening it a
little may increase the RPM for
feathering to take place properly.
Keeping your speed up may help as
well.
If the propeller fails to feather,
reduce your airspeed to a minimum
(but not below scheduled engine-out
climb speed) and allow the RPM to
stabilise as low as possible. Try
again. If feathering still fails, try to
reduce speed so the rotation ceases,
which will cause less of a drag
penalty than a windmilling prop,
even if it has stopped in fine pitch.
Not only will your single-engined
climbout performance be affected,
directional controllability will be,
too, though you should be OK
down to Vmca.
Twins
Flying twin-engined helicopters
requires a different philosophy in
many ways, certainly getting used to
not dumping the collective every
time an emergency happens, and
their complexity, although there is
no real change in flying
characteristics as there would be if
an engine fails in an aeroplane. You
also have takeoff and landing
profiles, in case something happens,
and performance charts, with
generally more shallow approaches
to comply with them.
The regulations require you to
ensure that your aircraft has
adequate performance for any
proposed flight. The "performance"
of an aircraft describes its ability to
maintain certain rates of climb
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
248 Operational Flying
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
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
　
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