Federal Aviation Administration, DOT

Pt. 25, App. C

APPENDIX C TO PART 25
Part I - Atmospheric Icing Conditions

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(a) Continuous maximum icing. The maximum continuous intensity of atmospheric
icing conditions (continuous maximum
icing) is defined by the variables of the cloud
liquid water content, the mean effective diameter of the cloud droplets, the ambient air
temperature, and the interrelationship of
these three variables as shown in figure 1 of
this appendix. The limiting icing envelope in
terms of altitude and temperature is given in
figure 2 of this appendix. The inter-relationship of cloud liquid water content with drop
diameter and altitude is determined from
figures 1 and 2. The cloud liquid water content for continuous maximum icing conditions of a horizontal extent, other than 17.4
nautical miles, is determined by the value of
liquid water content of figure 1, multiplied

by the appropriate factor from figure 3 of
this appendix.
(b) Intermittent maximum icing. The intermittent maximum intensity of atmospheric
icing conditions (intermittent maximum
icing) is defined by the variables of the cloud
liquid water content, the mean effective diameter of the cloud droplets, the ambient air
temperature, and the interrelationship of
these three variables as shown in figure 4 of
this appendix. The limiting icing envelope in
terms of altitude and temperature is given in
figure 5 of this appendix. The inter-relationship of cloud liquid water content with drop
diameter and altitude is determined from
figures 4 and 5. The cloud liquid water content for intermittent maximum icing conditions of a horizontal extent, other than 2.6
nautical miles, is determined by the value of
cloud liquid water content of figure 4 multiplied by the appropriate factor in figure 6 of
this appendix.