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flight attitude on the attitude indicator, airspeed will remain
relatively constant even when erroneous readings
are presented by the airspeed indicator.
TM 1-1520-240-10
8-4-4
8-4-30. Flight in Thunderstorms.
Flight in or in close proximity to thunderstorms is to be
avoided because of the accompanying severe turbulence
and restricted visibility. If a thunderstorm is inadvertently
encountered during flight, the procedures for
flight in turbulent air are to be followed and the flight path
altered to leave the area. Should a thunderstorm be encountered
during a night flight, the cockpit dome light
should be turned on with white light selected to minimize
the blinding effect of lightning. Refer to chapter 5 for
limitations.
8-4-31. Ice and Rain.
8-4-32. Ice.
The helicopter is equipped with pitot tube, AFCS yaw port
heating, and windshield anti-icing systems to enable safe
flight in light icing conditions. Operation of these systems
is described in Chapter 2. Additional information and
specific procedures are also included in this section under
Cold Weather Operations. The greatest damage
caused by ice accumulation is lowered rotor blade efficiency
resulting in decreased range and endurance. If
icing is encountered during IMC flight, consideration
must be given to reduced range and endurance due to
increased fuel consumption. Refer to chapter 5 for limitations.
8-4-33. Exterior Inspection.
Refer to paragraph 8-2-10.
8-4-34. Taxiing.
Taxi at slow speeds to ensure positive braking action
during turns. The forward tilt of the rotors will cause the
helicopter to continue moving forward if icy conditions
prevent braking.
8-4-35. Before Takeoff.
When the takeoff is to be accomplished into possible
icing conditions, the following are to be accomplished as
part of the Before Takeoff Check.
ANTI-ICE switches — ON. Refer to chapter 5 for limitations.
8-4-36. During Flight.
Since all of the systems on this helicopter are of the
anti-icing rather than the de-icing type, always start systems
at least 5 minutes before entering a suspect or
forecast icing area. In addition, engine icing can occur at
temperatures above freezing.
a. Extended flight in light icing conditions may result
in lateral and vertical vibrations caused by asymmetric
self-shedding of ice. Minor rotor blade damage may occur
from ice shedding at 10
C and below. One-per-rev
lateral vibrations from asymmetric shedding at any temperature
may occur. If vibrations are encountered, airspeed
should be reduced and the aircraft should be flown
out of the icing area.
b. Extended flight in icing conditions can result in ice
accumulating on the helicopter heater fuel drain. If the
heater shuts down during icing, do not attempt restart
until ice is removed from the heater intake, exhaust, and
heater fuel drain.
8-4-37. Approach and Landing.
Accomplish a normal approach and landing; but if icing
is present, increased power will be required. The forward
and aft wheels accumulate ice, which can result in the
brakes freezing. If icing conditions have been encountered,
a zero forward ground speed landing should be
accomplished.
8-4-38. Rain.
It is considered that rain will have no detrimental effect on
the flight characteristics or performance of the helicopter.
The windshield wipers should be adjusted to FAST during
an instrument approach in rain, as rain may present
a restriction to visibility. Pitot heat should be used for
flights in rain to prevent moisture from accumulating in
the pitot tube and AFCS yaw ports and tubing.
8-4-39. Salt Water Operation.
8-4-40. Power Deterioration.
Salt spray ingestion in turbine engines may result in a
loss in performance as well as a loss in compressor stall
margin. This reduction in stall margin makes the engine
susceptible to stalls during acceleration, and more particularly,
under deceleration conditions. As spray is ingested
and strikes the compressor blades and stator
vanes, salt is deposited. The resulting buildup gradually
changes the airfoil sections, which in turn affects performance.
This deterioration will be noticed as a decrease
in torque and an increase in PTIT for a given N1. Should
the deterioration reach the point where the compressor
actually stalls, PTIT will increase, while N1 and torque
will decrease. The circumstances under which power
deterioration may occur during salt water operation vary
with a number of factors. The flight regime, gross
weight,wind direction and velocity, pilot technique, duration
　
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