742 

14 CFR Ch. I (1–1–19 Edition) 

Pt.33, App. D 

Within the envelope, total water content 

(TWC) in g/m

3

has been determined based 

upon the adiabatic lapse defined by the con-
vective rise of 90% relative humidity air 
from sea level to higher altitudes and scaled 
by a factor of 0.65 to a standard cloud length 

of 17.4 nautical miles. Figure D2 of this Ap-
pendix displays TWC for this distance over a 
range of ambient temperature within the 
boundaries of the ice crystal envelope speci-
fied in Figure D1 of this Appendix. 

Ice crystal size median mass dimension 

(MMD) range is 50–200 microns (equivalent 
spherical size) based upon measurements 
near convective storm cores. 

The TWC can be treated as completely gla-

ciated (ice crystal) except as noted in the 
Table 1 of this Appendix. 

T

ABLE

1—S

UPERCOOLED

L

IQUID

P

ORTION OF

 

TWC 

Temperature range— 

deg C 

Horizontal cloud 

length—nautical miles 

LWC— 

g/m

3

 

0 to 

¥

20 ......................

≤

50 ..............................

≤

1.0 

T

ABLE

1—S

UPERCOOLED

L

IQUID

P

ORTION OF

 

TWC—Continued 

Temperature range— 

deg C 

Horizontal cloud 

length—nautical miles 

LWC— 

g/m

3

 

0 to 

¥

20 ......................

Indefinite ......................

≤

0.5 

< 

¥

20 ..........................

......................................

0 

The TWC levels displayed in Figure D2 of 

this Appendix represent TWC values for a 
standard exposure distance (horizontal cloud 
length) of 17.4 nautical miles that must be 
adjusted with length of icing exposure. 

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