460 

14 CFR Ch. I (1–1–19 Edition) 

Pt. 25, App. O 

PART I—METEOROLOGY 

In this Appendix icing conditions are de-

fined by the parameters of altitude, vertical 
and horizontal extent, temperature, liquid 
water content, and water mass distribution 
as a function of drop diameter distribution. 

(a) Freezing Drizzle (Conditions with spec-

tra maximum drop diameters from 100

µ

m to 

500 

µ

m): 

(1) Pressure altitude range: 0 to 22,000 feet 

MSL. 

(2) Maximum vertical extent: 12,000 feet. 
(3) Horizontal extent: Standard distance of 

17.4 nautical miles. 

(4) Total liquid water content. 

N

OTE

: Liquid water content (LWC) in 

grams per cubic meter (g/m

3

) based on hori-

zontal extent standard distance of 17.4 nau-
tical miles. 

(5) Drop diameter distribution: Figure 2. 
(6) Altitude and temperature envelope: 

Figure 3. 

(b) Freezing Rain (Conditions with spectra 

maximum drop diameters greater than 500 

µ

m): 

(1) Pressure altitude range: 0 to 12,000 ft 

MSL. 

(2) Maximum vertical extent: 7,000 ft. 
(3) Horizontal extent: Standard distance of 

17.4 nautical miles. 

(4) Total liquid water content. 

N

OTE

: LWC in grams per cubic meter (g/m

3

) 

based on horizontal extent standard distance 
of 17.4 nautical miles. 

(5) Drop Diameter Distribution: Figure 5. 
(6) Altitude and temperature envelope: 

Figure 6. 

(c) Horizontal extent. 
The liquid water content for freezing driz-

zle and freezing rain conditions for hori-
zontal extents other than the standard 17.4 
nautical miles can be determined by the 
value of the liquid water content determined 
from Figure 1 or Figure 4, multiplied by the 
factor provided in Figure 7, which is defined 
by the following equation: 

S = 1.266 

¥ 

0.213 log10(H) 

Where: 
S = Liquid Water Content Scale Factor 

(dimensionless) and 

H = horizontal extent in nautical miles 

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