459 

Federal Aviation Administration, DOT 

Pt. 25, App. O 

T

ABLE

2.—F

LIGHT

L

ENGTH

D

ISTRIBUTION

—Continued 

Flight length (NM) 

Airplane maximum range—nautical miles (NM) 

From  To  1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 

7000 

7200 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.4 0.7 0.8 

7200 

7400 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.5 0.7 

7400 

7600 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2 0.5 0.6 

7600 

7800 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.5 0.7 

7800 

8000 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.6 0.8 

8000 

8200 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.5 0.8 

8200 

8400 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.5 1.0 

8400 

8600 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.6 1.3 

8600 

8800 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.4 1.1 

8800 

9000 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2 0.8 

9000 

9200 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.5 

9200 

9400 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2 

9400 

9600 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 

9600 

9800 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 

9800 

10000 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 

(c) Overnight Temperature Drop. For air-

planes on which FRM is installed, the over-
night temperature drop for this appendix is 
defined using: 

(1) A temperature at the beginning of the 

overnight period that equals the landing 
temperature of the previous flight that is a 
random value based on a Gaussian distribu-
tion; and 

(2) An overnight temperature drop that is 

a random value based on a Gaussian distribu-
tion. 

(3) For any flight that will end with an 

overnight ground period (one flight per day 
out of an average number of flights per day, 
depending on utilization of the particular 
airplane model being evaluated), the landing 
outside air temperature (OAT) is to be cho-
sen as a random value from the following 
Gaussian curve: 

T

ABLE

3.—L

ANDING

O

UTSIDE

A

IR

T

EMPERATURE

 

Parameter 

Landing outside 

air temperature 

°

F 

Mean Temperature ..................................

58.68 

negative 1 std dev ...................................

20.55 

positive 1 std dev ....................................

13.21 

(4) The outside ambient air temperature 

(OAT) overnight temperature drop is to be 
chosen as a random value from the following 
Gaussian curve: 

T

ABLE

4.—O

UTSIDE

A

IR

T

EMPERATURE

(OAT) 

D

ROP

 

Parameter 

OAT drop 

temperature 

°

F 

Mean Temp ...................................................

12.0 

1 std dev ........................................................

6.0 

(d) Number of Simulated Flights Required 

in Analysis. In order for the Monte Carlo 
analysis to be valid for showing compliance 

with the fleet average and warm day flam-
mability exposure requirements, the appli-
cant must run the analysis for a minimum 
number of flights to ensure that the fleet av-
erage and warm day flammability exposure 
for the fuel tank under evaluation meets the 
applicable flammability limits defined in 
Table 5 of this appendix. 

T

ABLE

5.—F

LAMMABILITY

E

XPOSURE

L

IMIT

 

Minimum number of 

flights in Monte 

Carlo analysis 

Maximum 

acceptable Monte 

Carlo average fuel 

tank flammability 

exposure 

(percent) to meet 

3 percent 

requirements 

Maximum 

acceptable Monte 

Carlo average fuel 

tank flammability 

exposure 

(percent) to meet 
7 percent part 26 

requirements 

10,000 ....................

2.91 6.79 

100,000 ..................

2.98 6.96 

1,000,000 ...............

3.00 7.00 

[Doc. No. FAA–2005–22997, 73 FR 42495, July 
21, 2008, as amended by Doc. No. FAA–2018– 
0119, Amdt. 25–145, 83 FR 9169, Mar. 5, 2018] 

A

PPENDIX

O 

TO

P

ART

25—S

UPERCOOLED

 

L

ARGE

D

ROP

I

CING

C

ONDITIONS

 

This Appendix consists of two parts. Part I 

defines this Appendix as a description of 
supercooled large drop icing conditions in 
which the drop median volume diameter 
(MVD) is less than or greater than 40 

µ

m, the 

maximum mean effective drop diameter 
(MED) of Appendix C of this part continuous 
maximum (stratiform clouds) icing condi-
tions. For this Appendix, supercooled large 
drop icing conditions consist of freezing driz-
zle and freezing rain occurring in and/or 
below stratiform clouds. Part II defines ice 
accretions used to show compliance with the 
airplane performance and handling qualities 
requirements of subpart B of this part. 

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