Federal Aviation Administration, DOT

Pt. 25, App. O

(a) General. The most critical ice accretion
in terms of airplane performance and handling qualities for each flight phase must be
used to show compliance with the applicable
airplane performance and handling qualities
requirements for icing conditions contained
in subpart B of this part. Applicants must
demonstrate that the full range of atmospheric icing conditions specified in part I of
this Appendix have been considered, including drop diameter distributions, liquid water
content, and temperature appropriate to the
flight conditions (for example, configuration,
speed, angle of attack, and altitude).
(1) For an airplane certified in accordance
with Section 25.1420(a)(1), the ice accretions for each
flight phase are defined in part II, paragraph
(b) of this Appendix.
(2) For an airplane certified in accordance
with Section 25.1420(a)(2), the most critical ice accretion for each flight phase defined in part
II, paragraphs (b) and (c) of this Appendix,
must be used. For the ice accretions defined

in part II, paragraph (c) of this Appendix,
only the portion of part I of this Appendix in
which the airplane is capable of operating
safely must be considered.
(3) For an airplane certified in accordance
with Section 25.1420(a)(3), the ice accretions for each
flight phase are defined in part II, paragraph
(c) of this Appendix.
(b) Ice accretions for airplanes certified in
accordance with Section 25.1420(a)(1) or (2).
(1) En route ice is the en route ice as defined by part II, paragraph (c)(3), of this Appendix, for an airplane certified in accordance with Section 25.1420(a)(2), or defined by part II,
paragraph (a)(3), of Appendix C of this part,
for an airplane certified in accordance with
Section 25.1420(a)(1), plus:
(i) Pre-detection ice as defined by part II,
paragraph (b)(5), of this Appendix; and
(ii) The ice accumulated during the transit
of one cloud with a horizontal extent of 17.4
nautical miles in the most critical of the
icing conditions defined in part I of this Appendix and one cloud with a horizontal extent of 17.4 nautical miles in the continuous

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PART II - AIRFRAME ICE ACCRETIONS
FOR SHOWING COMPLIANCE WITH SUBPART B OF THIS PART