Part II – Airframe ice accretions
ED
Decision 2015/008/R
(a) General.
The most
critical ice accretion in terms of aeroplane performance and handling
qualities for each flight phase must be used to show compliance with the
applicable aeroplane performance and handling qualities requirements for icing
conditions contained in Subpart B. Applicants must demonstrate that the full
range of atmospheric icing conditions specified in part I of this appendix
have been considered, including drop diameter distributions, liquid water
content, and temperature appropriate to the flight conditions (for example,
configuration, speed, angle-of-attack, and altitude).
(1) For an aeroplane certified in accordance
with CS 25.1420(a)(1), the ice accretions for each flight phase are
defined in part II, paragraph (b) of this appendix.
(2) For an aeroplane certified in accordance
with CS 25.1420(a)(2), the most critical ice accretion for each flight
phase defined in part II, paragraphs (b) and (c) of this appendix, must be
used. For the ice accretions defined in part II, paragraph (c) of this
appendix, only the portion of part I of this appendix in which the aeroplane is
capable of operating safely must be considered.
(3) For an aeroplane certified in accordance
with CS 25.1420(a)(3), the ice accretions for each flight phase are
defined in part II, paragraph (c) of this appendix.
(b) Ice accretions for aeroplanes certified in
accordance with CS 25.1420(a)(1) or (a)(2).
(1) En-route ice is the en-route ice as
defined by part II, paragraph (c)(3), of this appendix, for an aeroplane
certified in accordance with CS 25.1420(a)(2), or defined by part II,
paragraph (a)(3), of Appendix C, for an aeroplane certified in accordance with
CS 25.1420(a)(1), plus:
(i) Pre-detection ice as defined by part II
paragraph (b)(5) of this appendix; and
(ii) The ice accumulated during the transit of
one cloud with a horizontal extent of 32.2 km (17.4 nautical miles) in the
most critical of the icing conditions defined in part I of this appendix and
one cloud with a horizontal extent of 32.2 km (17.4 nautical miles) in the
continuous maximum icing conditions defined in Appendix C.
(2) Holding ice is the holding ice defined by
part II, paragraph (c)(4), of this appendix, for an aeroplane certified in
accordance with CS 25.1420(a)(2), or defined by part II,
paragraph (a)(4) of Appendix C, for an aeroplane certified in accordance with CS
25.1420(a)(1), plus:
(i) Pre-detection ice as defined by part II,
paragraph (b)(5) of this appendix; and
(ii) The ice accumulated during the transit of
one cloud with a 32.2 km (17.4 nautical miles) horizontal extent in the
most critical of the icing conditions defined in part I of this appendix and
one cloud with a horizontal extent of 32.2 km (17.4 nautical miles) in
the continuous maximum icing conditions defined in Appendix C.
(iii) Except the total exposure to holding ice
conditions does not need to exceed 45 minutes
(3) Approach ice is the more critical of the
holding ice defined by part II, paragraph (b)(2) of this appendix, or the ice
calculated in the applicable paragraph (b)(3)(i) or (ii) of part II of this
appendix:
(i) For an aeroplane certified in accordance
with CS 25.1420(a)(2), the ice accumulated during descent from the
maximum vertical extent of the icing conditions defined in part I of
this appendix to 610 m (2 000 feet) above the landing surface in the
cruise configuration, plus transition to the approach configuration, plus:
(A) Pre-detection ice, as defined by part II, paragraph
(b)(5) of this appendix; and
(B) The ice accumulated during the transit at
610 m (2 000 feet) above the landing surface of one cloud with a
horizontal extent of 32.2 km (17.4 nautical miles) in the most critical
of the icing conditions defined in part I of this appendix and one cloud with a
horizontal extent of 32.2 km (17.4 nautical miles) in the continuous
maximum icing conditions defined in Appendix C.
(ii) For an aeroplane certified in accordance
with CS 25.1420(a)(1), the ice accumulated during descent from the
maximum vertical extent of the maximum continuous icing conditions defined in part I of
Appendix C to 610 m (2 000 feet) above the landing surface in the cruise
configuration, plus transition to the approach configuration, plus:
(A) Pre-detection ice, as defined by part II,
paragraph (b)(5) of this appendix; and
(B) The ice accumulated during the transit at
610 m (2 000 feet) above the landing surface of one cloud with a
horizontal extent of 32.2 km (17.4 nautical miles) in the most critical
of the icing conditions defined in part I of this appendix and one cloud with a
horizontal extent of 32.2 km (17.4 nautical miles) in the continuous
maximum icing conditions defined in Appendix C.
(4) Landing ice is the more critical of the
holding ice as defined by part II, paragraph (b)(2) of this appendix, or the
ice calculated in the applicable paragraph (b)(4)(i) or (ii) of part II of
this appendix:
(i) For an aeroplane certified in accordance
with CS 25.1420(a)(2), the ice accretion defined by part II, paragraph
(c)(5)(i) of this appendix, plus a descent from 610 m (2 000 feet) above
the landing surface to a height of 61 m (200 feet) above the landing surface
with a transition to the landing configuration in the icing conditions defined
in part I of this appendix, plus:
(A) Pre-detection ice, as defined in part II,
paragraph (b)(5) of this appendix; and
(B) The ice accumulated during an exit
manoeuvre, beginning with the minimum climb gradient required by
CS 25.119, from a height of 61 m (200 feet) above the landing surface
through one cloud with a horizontal extent of 32.2 km (17.4 nautical
miles) in the most critical of the icing conditions defined in part I of
this appendix and one cloud with a horizontal extent of 32.2 km
(17.4 nautical miles) in the continuous maximum icing conditions defined
in Appendix C.
(ii) For an aeroplane certified in accordance
with CS 25.1420(a)(1), the ice accumulated in the maximum continuous
icing conditions defined in Appendix C, during a descent from the maximum
vertical extent of the icing conditions defined in Appendix C, to 610 m
(2 000 feet) above the landing surface in the cruise configuration, plus
transition to the approach configuration and flying for 15 minutes at 610 m
(2 000 feet) above the landing surface, plus a descent from 610 m
(2 000 feet) above the landing surface to a height of 61 m (200 feet)
above the landing surface with a transition to the landing configuration,
plus:
(A) Pre-detection ice, as described by part II,
paragraph (b)(5) of this appendix; and
(B) The ice accumulated during an exit
manoeuvre, beginning with the minimum climb gradient required by CS 25.119,
from a height of 61 m (200 feet) above the landing surface through one cloud
with a horizontal extent of 32.2 km (17.4 nautical miles) in the most critical
of the icing conditions defined in part I of this appendix and one cloud with a
horizontal extent of 32.2 km (17.4 nautical miles) in the continuous maximum
icing conditions defined in Appendix C.
(5) Pre-detection ice is the ice accretion
before detection of Appendix O conditions that require exiting per
CS 25.1420(a)(1) and (a)(2). It is the pre-existing ice accretion that
may exist from operating in icing conditions in which the aeroplane is approved
to operate prior to encountering the icing conditions requiring an exit, plus
the ice accumulated during the time needed to detect the icing conditions,
followed by two minutes of further ice accumulation to take into account the
time for the flight crew to take action to exit the icing conditions,
including coordination with air traffic control.
(i) For an aeroplane certified in accordance
with CS 25.1420(a)(1), the pre-existing ice accretion must be based on the
icing conditions defined in Appendix C.
(ii) For an aeroplane certified in accordance
with CS 25.1420(a)(2), the pre-existing ice accretion must be based on
the more critical of the icing conditions defined in Appendix C, or the icing
conditions defined in part I of this appendix in which the aeroplane is
capable of safely operating.
(c) Ice accretions for aeroplanes certified in
accordance with CS 25.1420(a)(2) or CS 25.1420(a)(3).
For an
aeroplane certified in accordance with CS 25.1420(a)(2), only the portion
of the icing conditions of part I of this appendix in which the aeroplane is
capable of operating safely must be considered.
(1) Take-off ice is the most critical ice
accretion on unprotected surfaces, and any ice accretion on the protected
surfaces appropriate to normal ice protection system operation, occurring
between the end of the take-off distance and 122 m (400 feet) above the
take-off surface, assuming accretion starts at the end of the take-off
distance in the take-off maximum icing conditions defined in part I of this
appendix.
(2) Final take-off ice is the most critical
ice accretion on unprotected surfaces, and any ice accretion on the protected
surfaces appropriate to normal ice protection system operation, between 122 m
(400 feet) and either 457 m (1 500 feet) above the take-off surface, or
the height at which the transition from the take-off to the en-route
configuration is completed and VFTO is reached, whichever is
higher. Ice accretion is assumed to start at lift-off the end of the take-off
distance in the icing conditions defined in part I of this appendix.
(3) En-route ice is the most critical ice
accretion on the unprotected surfaces, and any ice accretion on the protected
surfaces appropriate 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
accretion on the unprotected surfaces, and any ice accretion on the protected
surfaces appropriate to normal ice protection system operation, resulting from
45 minutes of flight within a cloud with a 32.2 km (17.4 nautical miles)
horizontal 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 normal ice protection system operation, resulting 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 610 m
(2 000 feet) above the landing surface in the cruise configuration, plus
transition to the approach configuration and flying for 15 minutes at 610 m
(2 000 feet) above the landing surface; or
(ii) Holding ice as defined by part II,
paragraph (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 normal ice protection system operation, resulting from the more
critical of the:
(i) Ice accretion defined by part II,
paragraph (c)(5)(i), of this appendix, plus ice accumulated in the icing
conditions defined in part I of this appendix during a descent from 610 m
(2 000 feet) above the landing surface to a height of 61 m (200 feet)
above the landing surface with a transition to the landing configuration,
followed by a go-around at the minimum climb gradient required by CS 25.119,
from a height of 61 m (200 feet) above the landing surface to 610 m
(2 000 feet) above the landing surface, flying for 15 minutes at 610 m
(2 000 feet) above the landing surface in the approach configuration, and
a descent to the landing surface (touchdown) in the landing configuration; or
(ii) Holding ice as defined by part II
paragraph (c)(4) of this appendix.
(7) For both unprotected and protected parts,
the ice accretion for the take-off phase must be determined for the icing
conditions defined in part I of this appendix, using the following
assumptions:
(i) The aerofoils, control surfaces, and, if
applicable, propellers are free from frost, snow, or ice at the start of
take-off;
(ii) The ice accretion begins at lift-off;
(iii) The critical ratio of
thrust/power-to-weight;
(iv) Failure of the critical engine occurs at VEF;
and
(v) Crew activation of the ice protection
system is in accordance with a normal operating procedure provided in the
Aeroplane Flight Manual, except that after beginning the take-off roll, it
must be assumed that the crew takes no action to activate the ice protection
system until the aeroplane is at least 122 m (400 feet) above the
take-off surface.
(d) The ice accretion before the ice protection
system has been activated and is performing its intended function is the
critical ice accretion formed on the unprotected and normally protected
surfaces before activation and effective operation of the ice protection
system in the icing conditions defined in part I of this appendix. This ice
accretion only applies in showing compliance to CS 25.143(j)
and 25.207(h).
(e) In order to reduce the number of ice
accretions to be considered when demonstrating compliance with the
requirements of CS 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
as critical as the specific ice accretion defined for that flight phase.
Configuration differences and their effects on ice accretions must be taken
into account.
(f) The ice accretion that has the most
adverse effect on handling qualities may be used for aeroplane performance
tests provided any difference in performance is conservatively taken into
account.
[Amdt
25/16]