5-33. ICING LIMITATIONS (TYPICAL).
While in icing conditions, if there is an
needed to maintain airspeed in level flight,
a cumulative total of 2 or more inches of
unexplained decrease of 15 knots IAS, or
an unexplained deviation between pilots
and copilots airspeed indicators, the icing
environment should be exited as soon as
practicable. Ice accumulation on the pitot
tube assemblies could cause a complete
loss of airspeed indication.
The following conditions indicate a possible
accumulation of ice on the pitot tube assemblies and
unprotected aircraft surfaces. If any of these
conditions are observed, the icing environment should
be exited as soon as practicable.
a. Total ice accumulation of 2 inches or more on
the wing surfaces. Determination of ice thickness can
be accomplished by summing the estimated ice
thickness on the wing prior to each pneumatic boot
recommended ½inch accumulation).
b. A 30% increase in torque per engine required
to maintain an desired airspeed in level flight (not to
exceed 85% torque) when operating at recommended
c. A decrease in indicated airspeed of 15 knots
after entering the icing condition (not slower than 1.4
power off stall speed) if maintaining original power
setting in level flight. This is determined by comparing
preicing condition entry speed to the indicated speed
after a surface and antenna deice cycle is completed.
d. Any variations from normal indicated airspeed
between the pilots and copilots airspeed indicators.
5-34. ICING LIMITATIONS (SEVERE).
environmental conditions outside of those
for which the aircraft is certified. Flight in
freezing rain, freezing drizzle, or mixed
icing conditions (supercooled liquid water
and ice crystals) may result in a buildup on
capability of the ice protection system, or
may result in ice forming aft of these
protected surfaces. This ice may not shed
using ice protection systems, and may
seriously degrade the performance and
controllability of the aircraft.
a. During flight, severe icing conditions that
exceed those for which the aircraft is certified shall be
determined by the following visual cues. If one or
more of these visual cues exist, immediately request
priority handling from air traffic control to facilitate a
route or an altitude change to exit the icing conditions:
(1) Unusually extensive ice accreted on the
airframe in areas not normally observed to collect ice.
(2) Accumulation of ice on the upper (or
lower, as appropriate) surface of the wing aft of the
(3) Accumulation of ice on the propeller
spinner farther aft than normally observed.
b. Since the autopilot may mask tactile cues that
indicate adverse changes in handling characteristics,
use of the autopilot is prohibited when any of the visual
cues specified above exist, or when unusual lateral
trim requirements or autopilot trim warnings are
encountered while the aircraft is in icing conditions.
5-35. OXYGEN REQUIREMENTS.
a. One oxygen mask must be provided for each
passenger and crewmember. A minimum 10minute
supply of supplement oxygen shall be available during
flight at or above an altitude of 25,000 feet based on
the highest total aircraft oxygen flow rates.
b. In addition, sufficient oxygen will be carried
for each flight, assuming a decompression will occur at
the altitude or point of flight that is most critical from
the standpoint of oxygen need, and that after
decompression the aircraft will descend, in accordance
with the emergency procedures, to a flight altitude that