Code of Federal Regulations - Title 14

546

14 CFR Ch. I (1–1–14 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 liftoff and 400 feet above
the takeoff surface, assuming accretion
starts at liftoff in the takeoff maximum
icing conditions of part I, paragraph (c) 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 liftoff 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.

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

weight;

(4) Failure of the critical engine occurs at

; 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]

PPENDIX

ART

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.
(5) Operation and monitoring of aircraft

engines and systems.

(6) Command decisions.
(b)

Workload factors. The following work-

load factors are considered significant when

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