spaschal on DSK3GDR082PROD with CFR

Federal Aviation Administration, DOT

Pt. 25, App. O

(i) For an airplane certified in accordance
with Section 25.1420(a)(1), the pre-existing ice accretion must be based on the icing conditions
defined in Appendix C of this part.
(ii) For an airplane certified in accordance
with Section 25.1420(a)(2), the pre-existing ice accretion must be based on the more critical of
the icing conditions defined in Appendix C of
this part, or the icing conditions defined in
part I of this Appendix in which the airplane
is capable of safely operating.
(c) Ice accretions for airplanes certified in accordance with SectionSection 25.1420(a)(2) or (3). For an airplane
certified
in
accordance
with
Section 25.1420(a)(2), only the portion of the icing
conditions of part I of this Appendix in
which the airplane is capable of operating
safely must be considered.
(1) Takeoff ice is the most critical ice accretion on unprotected surfaces, and any ice accretion on the protected surfaces, occurring
between the end of the takeoff distance and
400 feet above the takeoff surface, assuming
accretion starts at the end of the takeoff distance in the icing conditions defined in part
I of this Appendix.
(2) Final takeoff ice is the most critical ice
accretion on unprotected surfaces, and any
ice accretion on the protected surfaces appropriate to normal ice protection system
operation, between 400 feet and either 1,500
feet above the takeoff surface, or the height
at which the transition from the takeoff to
the en route configuration is completed and
VFTO is reached, whichever is higher. Ice accretion is assumed to start at the end of the
takeoff distance in the icing conditions defined in part I of this Appendix.
(3) En route ice is the most critical ice accretion on the unprotected surfaces, and any
ice accretion on the protected surfaces appropriate to normal ice protection system
operation, during the en route flight phase in
the icing conditions defined in part I of this
Appendix.
(4) Holding ice is the most critical ice accretion on the unprotected surfaces, and any
ice accretion on the protected surfaces appropriate to normal ice protection system
operation, resulting from 45 minutes of flight
within a cloud with a 17.4 nautical miles horizontal extent in the icing conditions defined
in part I of this Appendix, during the holding
phase of flight.
(5) Approach ice is the ice accretion on the
unprotected surfaces, and any ice accretion
on the protected surfaces appropriate to normal ice protection system operation, resulting from the more critical of the:
(i) Ice accumulated in the icing conditions
defined in part I of this Appendix during a
descent from the maximum vertical extent
of the icing conditions defined in part I of
this Appendix, to 2,000 feet above the landing
surface in the cruise configuration, plus
transition to the approach configuration and

flying for 15 minutes at 2,000 feet above the
landing surface; or
(ii) Holding ice as defined by part II, paragraph (c)(4), of this Appendix.
(6) Landing ice is the ice accretion on the
unprotected surfaces, and any ice accretion
on the protected surfaces appropriate to normal ice protection system operation, resulting from the more critical of the:
(i) Ice accretion defined by part II, paragraph (c)(5)(i), of this Appendix, plus ice accumulated in the icing conditions defined in
part I of this Appendix during a descent from
2,000 feet above the landing surface to a
height of 200 feet above the landing surface
with a transition to the landing configuration, followed by a go-around at the minimum climb gradient required by Section 25.119,
from a height of 200 feet above the landing
surface to 2,000 feet above the landing surface, flying for 15 minutes at 2,000 feet above
the landing surface in the approach configuration, and a descent to the landing surface
(touchdown) in the landing configuration; or
(ii) Holding ice as defined by part II, paragraph (c)(4), of this Appendix.
(7) For both unprotected and protected
parts, the ice accretion for the takeoff phase
must be determined for the icing conditions
defined in part I of this Appendix, using the
following assumptions:
(i) The airfoils, control surfaces, and, if applicable, propellers are free from frost, snow,
or ice at the start of takeoff;
(ii) The ice accretion starts at the end of
the takeoff distance;
(iii) The critical ratio of thrust/power-toweight;
(iv) Failure of the critical engine occurs at
VEF; and
(v) Crew activation of the ice protection
system is in accordance with a normal operating procedure provided in the airplane
flight manual, except that after beginning
the takeoff roll, it must be assumed that the
crew takes no action to activate the ice protection system until the airplane is at least
400 feet above the takeoff surface.
(d) The ice accretion before the ice protection system has been activated and is performing its intended function is the critical
ice accretion formed on the unprotected and
normally protected surfaces before activation and effective operation of the ice protection system in the icing conditions defined in part I of this Appendix. This ice accretion only applies in showing compliance
to SectionSection 25.143(j) and 25.207(h).
(e) In order to reduce the number of ice accretions to be considered when demonstrating compliance with the requirements of Section 25.21(g), any of the ice accretions
defined in this Appendix may be used for any
other flight phase if it is shown to be at least

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