Roughness
Due toTail
Rotor Vortex
Ring State
F
11-14
5. Be aware that if a considerable amount of left
pedal is being maintained, a sufficient amount of
left pedal may not be available to counteract an
unanticipated right yaw.
6. Be alert to changing wind conditions, which may
be experienced when flying along ridge lines and
around buildings.
RECOVERY TECHNIQUE
If a sudden unanticipated right yaw occurs, the following
recovery technique should be performed. Apply full
left pedal while simultaneously moving cyclic control
forward to increase speed. If altitude permits, reduce
power. As recovery is effected, adjust controls for
normal forward flight.
Collective pitch reduction aids in arresting the yaw rate
but may cause an excessive rate of descent. Any large,
rapid increase in collective to prevent ground or
obstacle contact may further increase the yaw rate and
decrease rotor r.p.m. The decision to reduce collective
must be based on your assessment of the altitude
available for recovery.
If the rotation cannot be stopped and ground contact is
imminent, an autorotation may be the best course of
action. Maintain full left pedal until the rotation stops,
then adjust to maintain heading.
MAIN DRIVE SHAFT FAILURE
The main drive shaft, located between the engine and
the main rotor gearbox, transmits engine power to the
main rotor gearbox. In some helicopters, particularly
those with piston engines, a drive belt is used instead of
a drive shaft. A failure of the drive shaft or belt has the
same effect as an engine failure, because power is no
longer provided to the main rotor, and an autorotation
has to be initiated. There are a few differences,
however, that need to be taken into consideration. If the
drive shaft or belt breaks, the lack of any load on the
engine results in an overspeed. In this case, the throttle
must be closed in order to prevent any further damage.
In some helicopters, the tail rotor drive system
continues to be powered by the engine even if the main
drive shaft breaks. In this case, when the engine
unloads, a tail rotor overspeed can result. If this happens,
close the throttle immediately and enter an
autorotation.
HYDRAULIC FAILURES
Most helicopters, other than smaller piston powered
helicopters, incorporate the use of hydraulic actuators
to overcome high control forces. A hydraulic system
consists of actuators, also called servos, on each flight
control; a pump, which is usually driven by the main
rotor gearbox; and a reservoir to store the hydraulic
fluid. A switch in the cockpit can turn the system off,
although it is left on under normal conditions. A
pressure indicator in the cockpit may be installed to
monitor the system.
An impending hydraulic failure can be recognized by a
grinding or howling noise from the pump or actuators,
increased control forces and feedback, and limited
control movement. The corrective action required is
stated in detail in the appropriate rotorcraft flight
manual. However, in most cases, airspeed needs to be
reduced in order to reduce control forces. The hydraulic
switch and circuit breaker should be checked and
recycled. If hydraulic power is not restored, make a
shallow approach to a running or roll-on landing. This
technique is used because it requires less control force
and pilot workload. Additionally, the hydraulic system
should be disabled, by either pulling the circuit breaker
and/or placing the switch in the off position. The
reason for this is to prevent an inadvertent restoration
of hydraulic power, which may lead to overcontrolling
near the ground.
In those helicopters where the control forces are so
high that they cannot be moved without hydraulic
assistance, two or more independent hydraulic systems
may be installed. Some helicopters use hydraulic accumulators
to store pressure that can be used for a short
time while in an emergency if the hydraulic pump fails.
This gives you enough time to land the helicopter with
normal control.
GOVERNOR FAILURE
Governors automatically adjust engine power to maintain
rotor r.p.m. when the collective pitch is changed. If
the governor fails, any change in collective pitch
requires you to manually adjust the throttle to maintain
correct r.p.m. In the event of a high side governor
failure, the engine and rotor r.p.m. try to increase above
the normal range. If the r.p.m. cannot be reduced and
controlled with the throttle, close the throttle and enter
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