TM 55-1520-228-10
Change 11 8-17/(8-18 blank)
8-40. ICING CONDITIONS.
a. Intentional flight in any icing condition is prohib-
ited. If icing conditions are encountered during flight,
effort should be made to vacate the icing conditions.
b. If icing conditions become unavoidable, the pilot
should turn on pitot heat, windshield defroster and the
engine anti-ice system.
c. During flights in icing, the following conditions
may be experienced:
(1) Obscured forward field of view due to accu-
mulation on windscreen and chin bubbles. If windshield
defrosters fail to keep windshield clear of ice, side win-
dows may be used for visual reference during landing.
(2) One-per-rotor-revolution vibrations, from mild
to severe, caused by asymmetrical ice shedding on
main rotor system. Severity of vibration will depend on
temperature and amount of accumulation on blades
when ice shed occurs. Possibility of asymmetrical ice
shed occurring increases as outside air temperature
decreases.
(3) An increase in torque required to maintain a
constant airspeed and altitude due to ice accumulation
on the rotor system and possible degradation of the
ability to maintain autorotational rotor speed within oper-
ating limits.
d. Control activity cannot be depended upon to re-
move ice from the main rotor system. Vigorous control
movements should not be made in an attempt to reduce
low frequency vibrations caused by asymmetrical shed-
ding of ice from main rotor blades. These movements
may induce more asymmetrical shedding of ice, further
aggravating helicopter vibration levels.
WARNING
Ice shed from rotor blades and/or other
rotating components presents a
hazard to personnel during landing
and shutdown. Ground personnel
should remain clear of helicopter
during landing and shutdown;
passengers/crew members should not
exit aircraft until rotor has stopped
turning.
8-41. SAND AND DUST OPERATION.
Efficiency of the particle separator is directly related to
the amount of engine bleed air available. Bleed air is
used to operate the particle separator, and remove
sand/dust particles before they enter the engine plenum
chamber.
a. Ground Operations. At ground idle, with heater
on, particle separator with improved nozzles has a
cleaning efficiency of approximately 53%; with heater
off, cleaning efficiency is approximately 75%.
b. Extended Ground Operations. If extended
ground operations are expected, it is recommended
heater be turned off. Should environmental conditions
require use of heater, it is recommended OH-58 be op-
erated close to 100% N2 with blades in flat pitch. This
condition should permit particle separator to function at
a cleaning efficiency of over 70%.
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