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external wing stores.
9.5.3 Single Engine Failure Low Altitude/Low Airspeed
and Cruise.
Continued flight is possible.
1. LAND AS SOON AS PRACTICABLE.
Continued flight is not possible.
2. STORES JETT switches - Activate if
required.
3. LAND AS SOON AS POSSIBLE.
TM 1-1520-238-10
Figure 9-2. Height Velocity Plots (Sheet 1 of 2)
9-5
TM 1-1520-238-10
Figure 9-2. Height Velocity Plots (Sheet 2 of 2)
9 - 6
TM 1-1520-238-10
9.5.4 Dual Engine Failure.
WARNING
In the event of an inadvertent activation of the engine
chop collar, initial indications from Np and Nr could be
interpreted as a dual engine failure. Indications of
engine chop collar activation are the ENGINE CHOP
light illuminates and engine idle indications on the NG,
TGT and Np There is NO illumination of the ENGINE
OUT 1 or 2 lights on the MASTER CAUTION panel.
If both engines fail, immediate action is required to make
a safe autorotative descent. The altitude and airspeed at
which a two engine failure occurs will dictate the action to
be taken. After the failure, main rotor rpm will decay
rapidly and the aircraft will yaw to the left. Unless a twoengine
failure occurs near the ground, it is mandatory
that autorotation be established immediately. At gross
weights above 15,000 lbs, immediate consideration
should be given to jettisoning the external wing stores.
During cruise at airspeeds to Vne, reduce collective
immediately to regain Nr and then adjust as required to
maintain rpm. The cyclic should be adjusted as
necessary to attain and maintain airspeed in the
optimum range (fig 9-3) An airspeed between 64 and 98
KIAS should be maintained except for high altitude high
gross weight conditions where the maximum allowable
autorotation airspeed should be maintained if it is less
than 64 KIAS. A landing area must be selected
immediately after both engines fail, and control inputs
must be made to fly to the intended site. Throughout the
descent, adjust collective as necessary to maintain Nr
within normal range. At high gross weights, the rotor
may tend to overspeed and the collective must be used
to maintain the desired rotor rpm (fig
5-1). Nr should be maintained at or slightly above 100%
to allow ample rpm before touchdown, and heading
maintained by pedals.
Main rotor rpm will increase momentarily when the cyclic
is moved aft with no change in collective pitch setting.
An autorotative rpm of approximately 100% provides for
a good rate of descent. Nr above 100% may result in a
higher than desired rate of descent. At 100 to 125 feet
AGL, use aft cyclic to decelerate. This reduces airspeed
and rate of descent and causes an increase in Nr. The
degree of increase depends upon the amount and rate of
deceleration. An increase in Nr can be desirable in that
more inertial energy in the rotor system will be available
to cushion the landing. Ground contact should be made
with some forward speed. If a rough landing is selected,
a more pronounced deceleration is necessary and
touchdown speed should approach zero. It is possible
that during the autorotative approach, the situation may
require additional deceleration. In that case, it is
necessary to assume a landing attitude at a higher
altitude than normal. Should both engines fail at low
airspeed, initial collective reduction may vary widely. The
objective is to reduce collective as necessary to maintain
Nr within normal range. In some instances at low
altitude or low airspeed, settling may be so rapid that little
can be done to avoid a hard-impact landing.
In that case, it is critical to maintain a level landing
attitude. Cushion the landing with remaining collective
as helicopter settles to the ground.
9.5.5 Dual Engine Failure Low Altitude/Low Airspeed
and Cruise.
1. AUTOROTATE.
2. Chop Collar - Reset.
3. STORES JETT switches - Activate as desired
(time permitting)
Change 3 9-7
TM 1-1520-238-10
Figure 9-3. Autorotative Glide Chart
9-8
9.6 ENGINE COMPRESSOR STALL.
An engine compressor stall is normally recognized by a
noticeable bang or popping noise and possible aircraft
yaw. These responses are normally accompanied by a
rapid increase in TGT and fluctuations in NG, torque,
and Np readings for the affected engine. In the event of
a compressor stall:
1. Collective - Reduce,
If condition persists:
2. PWR lever (affected engine) - Retard. (TGT
should decrease.)
3. PWR lever (affected engine) - FLY.
If stall condition reoccurs:
4. PWR lever (affected engine) - IDLE.
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