Subchapters
- A (525.1-525.2),
- B (525.21-525.255),
- C (525.301-525.581),
- D (525.601-525.899),
- E (525.901-525.1207),
- F (525.1301-525.1461),
- G (525.1501-525.1587)
- H (525.1701-525.1733)
Appendices
A, B, C, D, E, F, G, H, I, J, K, L, M, N, O
Appendix C
Part I – Atmospheric Icing Conditions
(amended 2008/10/30; no previous version)
- (a) Continuous maximum icing.The maximum continuous intensity of atmospheric icing conditions (continuous maximum icing) is defined by the variables of the cloud liquid water content, the mean effective diameter of the cloud droplets, the ambient air temperature, and the interrelationship of these three variables as shown in Figure 1 of this Appendix. The limiting icing envelope in terms of altitude and temperature is given in Figure 2 of this Appendix. The inter-relationship of cloud liquid water content with drop diameter and altitude is determined from Figures 1 and 2. The cloud liquid water content for continuous maximum icing conditions of a horizontal extent, other than 17.4 nautical miles (32.225 km), is determined by the value of liquid water content of Figure 1, multiplied by the appropriate factor from Figure 3 of this Appendix.
(amended 2008/10/30; previous version) - (b) Intermittent maximum icing.The intermittent maximum intensity of atmospheric icing conditions (intermittent maximum icing) is defined by the variables of the cloud liquid water content, the mean effective diameter of the cloud droplets, the ambient air temperature, and the inter-relationship of these three variables as shown in Figure 4 of this Appendix. The limiting icing envelope in terms of altitude and temperature is given in Figure 5 of this Appendix. The inter-relationship of cloud liquid water content with drop diameter and altitude is determined from Figures 4 and 5. The cloud liquid water content for intermittent maximum icing conditions of a horizontal extent, other than 2.6 nautical miles (4.815 km), is determined by the value of cloud liquid water content of Figure 4 multiplied by the appropriate factor in Figure 6 of this Appendix.
(amended 2008/10/30; previous version) - (c) Take-off maximum icing. The maximum intensity of atmospheric icing conditions for take-off (take-off maximum icing) is defined by the cloud liquid water content of 0.35 g/m3, the mean effective diameter of the cloud droplets of 20 microns, and the ambient air temperature at ground level of minus 9 degrees Celsius (-9° C). The take-off maximum icing conditions extend from ground level to a height of 1,500 feet above the level of the take-off surface.
(amended 2008/10/30; no previous version)
Part II - Airframe Ice Accretions for Showing Compliance with Subchapter B
(amended 2008/10/30; no previous version)
- (a) Ice accretions - General. The most critical ice accretion in terms of aeroplane performance and handling qualities for each flight phase shall be used to show compliance with the applicable aeroplane performance and handling requirements in icing conditions of subchapter B of this chapter. Applicants shall demonstrate that the full range of atmospheric icing conditions specified in Part I of this Appendix have been considered, including the mean effective diameter of the cloud droplets, liquid water content, and temperature appropriate to the flight conditions (for example, configuration, speed, angle-of-attack, and altitude). The ice accretions for each flight phase are defined as follows:
(amended 2008/10/30; no previous version)- (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 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.
(effective 2021/04/08) - (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 400 feet and either 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 the end of the take-off distance in the take-off maximum icing conditions of Part I, paragraph (c) of this Appendix.
(effective 2021/04/08) - (3) En route ice is the critical ice accretion on unprotected surfaces and any ice accretion on the protected surfaces appropriate to normal ice protection system operation, during the en route phase.
(amended 2008/10/30; no previous version) - (4) Holding ice is the critical ice accretion on unprotected surfaces and any ice accretion on the protected surfaces appropriate to normal ice protection system operation, during the holding flight phase.
(amended 2008/10/30; no previous version) - (5) Approach ice is the critical ice accretion on unprotected surfaces and any ice accretion 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.
(amended 2008/10/30; no previous version) - (6) Landing ice is the critical ice accretion on unprotected surfaces and any ice accretion on the protected surfaces appropriate to normal ice protection system operation following exit from the approach flight phase and transition to the final landing configuration.
(amended 2008/10/30; no previous version)
- (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 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.
- (b) In order to reduce the number of ice accretions to be considered when demonstrating compliance with the requirements of 525.21(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 shall be taken into account.
(amended 2008/10/30; no previous version) - (c) 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.
(amended 2008/10/30; no previous version) - (d) For both unprotected and protected parts, the ice accretion for the take-off phase may be determined by calculation, assuming the take-off maximum icing conditions defined in Appendix C, and assuming that:
(amended 2008/10/30; no previous version)- (1) Airfoils control surfaces and, if applicable, propellers are free from frost, snow, or ice at the start of the take-off;
(amended 2008/10/30; no previous version) - (2) The ice accretion starts at the end of the take-off distance;
(effective 2021/04/08) - (3) The critical ratio of thrust/power-to-weight is used;
(amended 2008/10/30; no previous version) - (4) Failure of the critical engine occurs at VEF; and
(amended 2008/10/30; no previous version) - (5) Flight 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 shall be assumed that the flight crew takes no action to activate the ice protection system until the aeroplane is at least 400 feet above the take-off surface.
(amended 2008/10/30; no previous version)
- (1) Airfoils control surfaces and, if applicable, propellers are free from frost, snow, or ice at the start of the take-off;
- (e) 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 continuous maximum atmospheric icing conditions. This ice accretion only applies in showing compliance to 525.143(j), 525.207(h) and 525.207(i).
(effective 2014/11/30)
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
