469 

Federal Aviation Administration, DOT 

Pt. 25, App. O 

(i) For an airplane certified in accordance 

with § 25.1420(a)(1), the pre-existing ice accre-
tion must be based on the icing conditions 
defined in Appendix C of this part. 

(ii) For an airplane certified in accordance 

with § 25.1420(a)(2), the pre-existing ice accre-
tion must be based on the more critical of 
the icing conditions defined in Appendix C of 
this part, or the icing conditions defined in 
part I of this Appendix in which the airplane 
is capable of safely operating. 

(c) 

Ice accretions for airplanes certified in ac-

cordance with §§ 25.1420(a)(2) or (3). 

For an air-

plane certified in accordance with 
§ 25.1420(a)(2), only the portion of the icing 
conditions of part I of this Appendix in 
which the airplane is capable of operating 
safely must be considered. 

(1) 

Takeoff ice 

is the most critical ice accre-

tion on unprotected surfaces, and any ice ac-
cretion on the protected surfaces, occurring 
between the end of the takeoff distance and 
400 feet above the takeoff surface, assuming 
accretion starts at the end of the takeoff dis-
tance in the icing conditions defined in part 
I of this Appendix. 

(2) 

Final takeoff ice 

is the most critical ice 

accretion on unprotected surfaces, and any 
ice accretion on the protected surfaces ap-
propriate to normal ice protection system 
operation, between 400 feet and either 1,500 
feet above the takeoff surface, or the height 
at which the transition from the takeoff to 
the en route configuration is completed and 
V

FTO

is reached, whichever is higher. Ice ac-

cretion is assumed to start at the end of the 
takeoff distance in the icing conditions de-
fined in part I of this Appendix. 

(3) 

En route ice 

is the most critical ice ac-

cretion on the unprotected surfaces, and any 
ice accretion on the protected surfaces ap-
propriate to normal ice protection system 
operation, during the en route flight phase in 
the icing conditions defined in part I of this 
Appendix. 

(4) 

Holding ice 

is the most critical ice ac-

cretion on the unprotected surfaces, and any 
ice accretion on the protected surfaces ap-
propriate to normal ice protection system 
operation, resulting from 45 minutes of flight 
within a cloud with a 17.4 nautical miles hor-
izontal extent in the icing conditions defined 
in part I of this Appendix, during the holding 
phase of flight. 

(5) 

Approach ice 

is the ice accretion on the 

unprotected surfaces, and any ice accretion 
on the protected surfaces appropriate to nor-
mal ice protection system operation, result-
ing from the more critical of the: 

(i) Ice accumulated in the icing conditions 

defined in part I of this Appendix during a 
descent from the maximum vertical extent 
of the icing conditions defined in part I of 
this Appendix, to 2,000 feet above the landing 
surface in the cruise configuration, plus 
transition to the approach configuration and 

flying for 15 minutes at 2,000 feet above the 
landing surface; or 

(ii) Holding ice as defined by part II, para-

graph (c)(4), of this Appendix. 

(6) 

Landing ice 

is the ice accretion on the 

unprotected surfaces, and any ice accretion 
on the protected surfaces appropriate to nor-
mal ice protection system operation, result-
ing from the more critical of the: 

(i) Ice accretion defined by part II, para-

graph (c)(5)(i), of this Appendix, plus ice ac-
cumulated in the icing conditions defined in 
part I of this Appendix during a descent from 
2,000 feet above the landing surface to a 
height of 200 feet above the landing surface 
with a transition to the landing configura-
tion, followed by a go-around at the min-
imum climb gradient required by § 25.119, 
from a height of 200 feet above the landing 
surface to 2,000 feet above the landing sur-
face, flying for 15 minutes at 2,000 feet above 
the landing surface in the approach configu-
ration, and a descent to the landing surface 
(touchdown) in the landing configuration; or 

(ii) Holding ice as defined by part II, para-

graph (c)(4), of this Appendix. 

(7) For both unprotected and protected 

parts, the ice accretion for the takeoff phase 
must be determined for the icing conditions 
defined in part I of this Appendix, using the 
following assumptions: 

(i) The airfoils, control surfaces, and, if ap-

plicable, propellers are free from frost, snow, 
or ice at the start of takeoff; 

(ii) The ice accretion starts at the end of 

the takeoff distance; 

(iii) The critical ratio of thrust/power-to- 

weight; 

(iv) Failure of the critical engine occurs at 

V

EF

; and 

(v) Crew activation of the ice protection 

system is in accordance with a normal oper-
ating procedure provided in the airplane 
flight manual, except that after beginning 
the takeoff roll, it must be assumed that the 
crew takes no action to activate the ice pro-
tection system until the airplane is at least 
400 feet above the takeoff surface. 

(d) The ice accretion before the ice protec-

tion system has been activated and is per-
forming its intended function is the critical 
ice accretion formed on the unprotected and 
normally protected surfaces before activa-
tion and effective operation of the ice pro-
tection system in the icing conditions de-
fined in part I of this Appendix. This ice ac-
cretion only applies in showing compliance 
to §§ 25.143(j) and 25.207(h). 

(e) In order to reduce the number of ice ac-

cretions to be considered when dem-
onstrating compliance with the require-
ments of § 25.21(g), any of the ice accretions 
defined in this Appendix may be used for any 
other flight phase if it is shown to be at least 

VerDate Sep<11>2014 

12:50 Apr 30, 2019

Jkt 247046

PO 00000

Frm 00479

Fmt 8010

Sfmt 8002

Y:\SGML\247046.XXX

247046

spaschal on DSK3GDR082PROD with CFR