390 

14 CFR Ch. I (1–1–19 Edition) 

Pt. 25, App. D 

Part II—Airframe Ice Accretions for Showing 

Compliance With Subpart B. 

(a) 

Ice accretions—General. 

The most crit-

ical ice accretion in terms of airplane per-
formance and handling qualities for each 
flight phase must be used to show compli-
ance with the applicable airplane perform-
ance and handling requirements in icing con-
ditions of subpart B of this part. Applicants 
must demonstrate that the full range of at-
mospheric icing conditions specified in part I 
of this appendix have been considered, in-
cluding the mean effective drop diameter, 
liquid water content, and temperature appro-
priate to the flight conditions (for example, 
configuration, speed, angle-of-attack, and al-
titude). The ice accretions for each flight 
phase are defined as follows: 

(1) 

Takeoff ice 

is the most critical ice accre-

tion on unprotected surfaces and any ice ac-
cretion on the protected surfaces appropriate 
to normal ice protection system operation, 
occurring between the end of the takeoff dis-
tance and 400 feet above the takeoff surface, 
assuming accretion starts at the end of the 
takeoff distance in the takeoff maximum 
icing conditions defined in part I of this Ap-
pendix. 

(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 takeoff maximum 
icing conditions of part I, paragraph (c) of 
this Appendix. 

(3) 

En route ice 

is the critical ice accretion 

on the unprotected surfaces, and any ice ac-
cretion on the protected surfaces appropriate 
to normal ice protection system operation, 
during the en route phase. 

(4) 

Holding ice 

is the critical ice accretion 

on the unprotected surfaces, and any ice ac-
cretion on the protected surfaces appropriate 
to normal ice protection system operation, 
during the holding flight phase. 

(5) 

Approach ice 

is the critical ice accretion 

on the unprotected surfaces, and any ice ac-
cretion on the protected surfaces appropriate 
to normal ice protection system operation 
following exit from the holding flight phase 
and transition to the most critical approach 
configuration. 

(6) 

Landing ice 

is the critical ice accretion 

on the unprotected surfaces, and any ice ac-
cretion on the protected surfaces appropriate 
to normal ice protection system operation 
following exit from the approach flight phase 
and transition to the final landing configura-
tion. 

(b) 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 paragraph (a) of this section may 
be used for any other flight phase if it is 
shown to be more critical than the specific 
ice accretion defined for that flight phase. 
Configuration differences and their effects 
on ice accretions must be taken into ac-
count. 

(c) The ice accretion that has the most ad-

verse effect on handling qualities may be 
used for airplane performance tests provided 
any difference in performance is conserv-
atively taken into account. 

(d) For both unprotected and protected 

parts, the ice accretion for the takeoff phase 
may be determined by calculation, assuming 
the takeoff maximum icing conditions de-
fined in appendix C, and assuming that: 

(1) Airfoils, control surfaces and, if appli-

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

(2) The ice accretion starts at the end of 

the takeoff distance. 

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

weight; 

(4) Failure of the critical engine occurs at 

V

EF

; and 

(5) 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. 

(e) 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 continuous maximum at-
mospheric icing conditions. This ice accre-
tion only applies in showing compliance to 
§§ 25.143(j) and 25.207(h), and 25.207(i). 

[Doc. No. 4080, 29 FR 17955, Dec. 18, 1964, as 
amended by Amdt. 25–121, 72 FR 44669, Aug. 8, 
2007; 72 FR 50467, Aug. 31, 2007; Amdt. 25–129, 
74 FR 38340, Aug. 3, 2009; Amdt. 25–140, 79 FR 
65528, Nov. 4, 2014] 

A

PPENDIX

D 

TO

P

ART

25 

Criteria for determining minimum flight crew. 

The following are considered by the Agency 
in determining the minimum flight crew 
under § 25.1523: 

(a) 

Basic workload functions. 

The following 

basic workload functions are considered: 

(1) Flight path control. 
(2) Collision avoidance. 
(3) Navigation. 
(4) Communications. 

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