8 the airplane is operating in Appendix O icing conditions. Following detection, the airplane must be capable of operating safely while exiting all icing conditions. If the applicant seeks certification for safe operation in portions of Appendix O conditions, such as freezing drizzle only, or during specific phases of flight, § 25.1420(a)(2) applies. If this option is chosen, following detection of conditions that exceed the selected portion of Appendix O, the airplane must be capable of operating safely while exiting all icing conditions. Certification for a portion of Appendix O (§ 25.1420(a)(2)) or none of Appendix O (§ 25.1420(a)(1)) requires substantiated methods of alerting the flightcrew when those portions of Appendix O are exceeded (§ 25.1420(a)(2)) or when Appendix O conditions are encountered (§ 25.1420(a)(1)). Section 25.1420(a)(3) applies when the applicant seeks certification for all of the icing conditions described in Appendix O. An airplane certified to § 25.1420(a)(3) must be capable of safely operating throughout the conditions described in Appendix O and does not need a means to detect Appendix O conditions. In effect, when § 25.1420(a)(3) is chosen, the airplane is certificated for flight in icing without any specific AFM procedures or limitations to exit icing conditions.
Note: While this AC provides guidance for compliance with § 25.1420(a)(2), further advancements in engineering tools may be necessary before an applicant is able to substantiate compliance with this option. A 2009 review of engineering tool capabilities found that current technology does not support distinguishing between freezing drizzle and freezing rain in flight. Therefore, certification for a portion of Appendix O will be challenging and will require close coordination with certifying authorities. Consult Appendix E of this AC for additional details on engineering tool capabilities.
6.1.4 Appendix O defines freezing drizzle and freezing rain environments by using four spectra of drop sizes with associated liquid water content (LWC) limits. An FAA detailed report on the development of Appendix O is available from the FAA William J.
Hughes Technical Center (see FAA Technical Report DOT/FAA/AR-09/10, Data and Analysis for the Development of an Engineering Standard for Supercooled Large Drop Conditions, dated March 2009). Following are the four drop size spectra:
6.1.4.1 Freezing drizzle environment with a median volume diameter (MVD) less than 40 microns (µm). In addition to drizzle drops, which are defined as measuring 100 µm to 500 µm in diameter, this environment contains drops less than 100 µm, with a sufficient number of drops less than 40 µm so the MVD is less than 40 µm.
6.1.4.2 Freezing drizzle environment with an MVD greater than 40 µm. In addition to freezing drizzle drops, this environment contains smaller drops, with diameters less than 100 µm.
6.1.4.3 Freezing rain environment with an MVD less than 40 µm. In addition to freezing rain drops, which are defined as measuring more than 500 µm in diameter, this environment also contains smaller drops of less than 500 µm with a sufficient number of drops less than 40 µm so the MVD is less than 40 µm.
6.1.4.4 Freezing rain environment with an MVD greater than 40 µm. In addition to freezing rain drops, this environment also contains smaller drops of less than 100 µm.
6.1.5 Initial certification for flight in a portion of Appendix O conditions will likely include all of freezing drizzle or all of freezing rain. Such certification could be restricted to operation in Appendix O conditions by phase of flight. Certification for flight in a portion of Appendix O conditions depends on the applicant substantiating an acceptable way for the flightcrew to distinguish the portion of Appendix O conditions for which the airplane is certified from the portion of Appendix O conditions for which the airplane is not approved. Certification for a portion of Appendix O allows latitude for certification with a range of techniques. Ice shapes will need to be developed to test for the portion of the envelope for which the airplane is approved, as well as for detecting and exiting icing conditions beyond the selected portion.
6.1.6 Ice shapes developed using the approved portion of the icing envelope should account for the range of drop distribution and water content and consider the proposed method for identifying icing conditions that must be exited. The definition of the certificated portion of Appendix O for a particular airplane should be based on measured characteristics of the selected icing environment and be consistent with methods used for developing Appendix O.
6.1.7 Water content versus drop size relationships defined in Appendix C, figures 1 and 4, are defined in terms of mean effective diameter. Part 25 does not require consideration of specific distributions for Appendix C icing conditions. As referenced in FAA Technical Report DOT/FAA/CT-88/8-1 and AC 20-73A, single mode distributions such as Langmuir distributions have been used to represent the range of drop sizes and water content associated with a specific Appendix C icing condition.
6.1.8 The distributions assumed for Appendix C icing conditions are not appropriate for freezing precipitation icing conditions. This is because these icing conditions often consist of small and large drops that are bi-modally distributed. Langmuir type distributions cannot capture the bi-modal characteristic. Consequently, distributions of drop sizes are defined as part of Appendix O. The need to include distributions comes from the fact that a larger percentage of the cloud’s total water mass is contained in the larger diameter drops of Appendix O. The water mass of larger drops affects the water catch on airplane components. It also affects drop impingement, icing limits, and the ice build-up shape. Ice accretions resulting from the water catch must be considered for their effects on safe flight of the airplane.
6.1.9 Liquid water content maximum values for freezing drizzle and freezing rain decrease as temperature decreases. This is defined in Appendix O, figures 1 and 4, respectively.
Appendix O values of total liquid water follow the same standard as those in Appendix C. They represent liquid water content for a horizontal extent distance of 17.4 nautical miles (20 statute miles).
6.1.10 The maximum vertical extent distance of 12,000 feet for freezing drizzle includes the cloud layer and all drizzle precipitation below the cloud that is within 12,000 feet of the cloud top. The maximum altitude of freezing drizzle is the same as that for an Appendix C continuous maximum icing cloud—22,000 feet (Appendix O, figure 3).
Temperatures range to as low as -13 °F (-25 °C).
6.1.11 The maximum vertical extent distance for freezing rain is 7,000 feet. The maximum altitude of freezing rain is 12,000 feet. Temperatures range to as low as 8.6 °F (-13 °C).
6.1.12 It is not appropriate to use the United States Standard Atmosphere Temperature Lapse Rate with Altitude for freezing drizzle and freezing rain. Typically, freezing rain is associated with temperature inversions. Freezing drizzle is associated with other deviations from the standard lapse rate. When generating ice shapes associated with vertical transits through freezing drizzle and freezing rain, the critical temperature should be determined and used for the duration of the vertical exposure.
6.1.13 Liquid water content of continuous freezing drizzle and freezing rain decreases as the length of the precipitation area, or its horizontal extent, increases. The horizontal extent of an airplane’s exposure to freezing drizzle and freezing rain can be anywhere from a brief encounter to an extended one. An “f-factor” is used in Appendix O to calculate liquid water content per cubic meter based on the length of the cloud (its horizontal extent). The f-factor used in Appendix O is the same as is used in Appendix C for these calculations. This f-factor is discussed in appendix N of AC 20-73A.
6.2 Use of Icing Envelopes.
6.2.1 AC 20-73A addresses the use of Appendix C. Use of Appendix C is not changed by the addition of Appendix O. Appendix O is designed to be similar to Appendix C and to be used in much the same manner. The principal differences between using Appendix O and using Appendix C are that for Appendix O, the applicant must now—
6.2.1.1 Consider four icing conditions rather than two when determining critical icing conditions, and
6.2.1.2 Address drop size distributions.
6.2.2 Applications of drop size distributions typically require a bin tabulation of the proportion of mass (liquid water content) to drop diameter. Table 1 and table 2, which follow, represent 10-bin tabulations for the cumulative distributions in Appendix O.
Mass proportions for the bins were selected to provide a reasonable resolution of the upper range of the distributions. The shaded columns (a) and (b) in the tables contain values typically used as input to ice accretion computer codes. For some simulation techniques, different methods of segregating the bins may be appropriate.
11 Table 1. Freezing Drizzle Drop Size Distributions Represented Using 10 Bins
Freezing Drizzle Environment with MVD<40 μm Freezing Drizzle Environment with MVD>40 μm
(a) (b) (b) Bin Proportion of Mass Left Boundary Point (μm) Mass- Weighted Midpoint (μm) Right Boundary Point (μm) Left Boundary Point (μm) Mass- Weighted Midpoint (μm) Right Boundary Point (μm) 1 0.100 1 9 10 1 11 15 2 0.200 10 13 16 15 22 36 3 0.200 16 18 20 36 64 106 4 0.200 20 23 27 106 150 197 5 0.100 27 29 33 197 221 247 6 0.050 33 36 40 247 261 276 7 0.050 40 48 66 276 292 309 8 0.050 66 97 137 309 330 354 9 0.025 137 163 202 354 370 390 10 0.025 202 252 388 390 417 473 Note: Drop size distributions in one-micron-drop bin resolution are available in electronic files from the William J. Hughes Technical Center.
12 Table 2. Freezing Rain Drop Size Distributions Represented Using 10 Bins
Freezing Rain Environment with MVD < 40 μm Freezing Rain Environment with MVD > 40 μm
(a) (b) (b) Bin Proportion of Mass Left Boundary Point (μm) Mass- Weighted Midpoint (μm) Right Boundary Point (μm) Left Boundary Point (μm) Mass- Weighted Midpoint (μm) Right Boundary Point (μm) 1 0.100 1 7 8 1 9 14 2 0.200 8 10 12 14 35 236 3 0.200 12 15 19 236 399 526 4 0.200 19 25 53 526 645 765 5 0.100 53 255 468 765 833 912 6 0.050 468 534 595 912 957 1008 7 0.050 595 655 718 1008 1066 1129 8 0.050 718 792 883 1129 1197 1288 9 0.025 883 942 1034 1288 1345 1420 10 0.025 1034 1191 1553 1420 1545 2228 Note: Drop size distributions in one-micron-drop bin resolution are available in electronic files from the William J. Hughes Technical Center.
6.2.3 When compared with the Langmuir distributions of drop sizes commonly associated with Appendix C clouds, Appendix O drop size distributions have much larger drop sizes and a larger percentage of the total water mass in large drop sizes. The liquid water contents associated with icing conditions in Appendix O are different from those associated with Appendix C. These differences may affect water collection efficiency.
They may result in impingement limits that are further aft for Appendix O icing conditions than they are for Appendix C icing conditions. For more discussion of the effects of drop size and trajectory influence, see FAA Technical Report DOT/FAA/CT-88/8-1 and AC 20-73A.
6.2.4 An additional effect of the supercooled large drop environment is the variability in distribution of drop sizes. Ice shapes developed to simulate Appendix C icing
13 conditions are sometimes calculated by using a monodispersed drop distribution. This is because predicted main ice shapes are not highly sensitive to commonly assumed distributions for Appendix C (such as the Langmuir distributions). In a monodispersed drop distribution, all drop diameters are assumed to be equal to the MVD. The large variations of drop size and the larger percentages of water in the larger drops defined by Appendix O tend to magnify effects of distributed drop sizes. This may be reflected in the main ice shape and in runback ice characteristics.
7 CERTIFICATION PLAN.
At the start of the design and development of an airplane, the applicant should submit a certification plan that addresses the IPS to the appropriate FAA aircraft certification office (ACO) for approval. This certification plan should include the following basic information:
7.1 A general description of the airplane that includes dimensions, airworthiness limitations, and other data that may be relevant to the airplane’s IPS.
7.2 Description of the IPS.
7.3 A compliance checklist addressing each section of part 25 applicable to the IPS.
7.4 Identification of the certification methods for each applicable section of part 25, including a description of analyses and tests or references to similarity of designs, that the applicant intends to use for certifying the IPS. The applicant and the FAA should agree on these compliance means early in the certification program and before certification testing begins.
7.5 A failure hazard assessment to determine the criticality of the system.
7.6 If the ice protection or detection system contains software, software plans as described in Radio Technical Commission for Aeronautics (RTCA) DO-178C, Software Considerations in Airborne Systems and Equipment Certification (or another acceptable means of compliance for software).
7.7 Projected schedules of design, analyses, testing, and reporting.
7.8 A list of any anomalous results from completed icing certification tests (relevant to the requirements of 14 CFR 33.68 and 33.77) that will require special operating procedures unless this information is provided in a separate certification document or other airworthiness approved documentation.
7.9 If the IPS or icing detection system contains complex electronic hardware (such as programmable logic devices or application-specific integrated circuits), plans for providing a level of design assurance for these devices commensurate with their potential contribution to airplane hazards and system failures. Such hazards or failures could result from electronic hardware faults or malfunctions. The applicant should consult RTCA DO-254, Design Assurance Guidance for Airborne Electronic Hardware,
14 and RTCA DO-160G, Environmental Conditions and Test Procedures for Airborne Equipment, on how to provide design assurance for these devices.
8 ANALYSIS.
The applicant should prepare analyses to substantiate the choice of ice protection equipment for the airplane. Such analyses should clearly state the basic protection required and assumptions made, and delineate the methods of analysis used. All analyses should be validated by tests or should have been validated by the applicant on a previous certification program. The applicant who uses a previously validated method should substantiate why that method is applicable to the new program.
8.1 Analytical Simulation Methods.
Analytical simulation methods for icing include impingement and accretion models based on computational fluid dynamics (CFD). The applicant will typically use these methods to evaluate protected as well as unprotected areas for potential ice accretions.
Analytical simulation provides a way to account for the variability in drop distributions.
It also makes it possible to examine impingement in relation to visual icing cues and to analyze the location of detection devices for detrimental local flow effects.
8.2 Substantiating Icing Simulation Analytical Tools.
8.2.1 The substantiation process for icing simulation analytical tools, such as icing codes and cross comparisons, should be made with data derived from using other types of tools to show that the analytical simulation results are equivalent or conservative. Other types of test data that the icing simulation analytical tool data could be compared with are:
• Natural icing flight test data.
• Tanker test data.
• Icing tunnel data.
• Icing tunnel data.
8.2.2 Results of analysis with icing codes, as well as results of icing tunnel tests and tanker tests, should be compared to results of natural icing flight tests in Appendix C conditions that are required by § 25.1419. Engineering judgment is required when evaluating these comparisons because most simulation tools are steady-state simulations and they will be compared with tests made in natural icing conditions, which are variable. See AC 20-73A for additional guidance about substantiating icing simulation tools. The guidance in this paragraph applies to airframe, engine, and propeller icing tools for Appendix C and the applicable portion of Appendix O.
8.3 Analysis of Areas and Components to be Protected.
In evaluating the airplane’s ability to operate safely in Appendix C icing conditions and relevant icing conditions of Appendix O, and in determining which components will be protected, the applicant should examine those areas listed in AC 20-73A to determine the degree of protection required. An applicant may determine that protection is not
15 required for one or more of these areas or components. If so, the applicant’s analysis should include the supporting data and rationale for allowing those areas or components to remain unprotected. The applicant should show that the lack of protection does not adversely affect handling characteristics or performance of the airplane, as required by § 25.21(g). The applicant must also show that the lack of protection does not affect the operation and functioning of affected systems and equipment (e.g., pitot probes).
Accessory cooling air intakes that face the airstream could become restricted with ice accretion. Inlets (including National Advisory Committee for Aeronautics (NACA) inlets) that do not accrete ice in Appendix C conditions may accrete ice in Appendix O conditions.
8.4 Flutter Analysis.
AC 25.629-1B, Aeroelastic Stability Substantiation of Transport Category Airplanes, provides guidance for showing compliance with § 25.629. For airplanes approved for operation in icing conditions, that AC addresses nominal configurations with ice accumulations on unprotected surfaces as well as ice accumulations resulting from any single failure in the deicing system or any combination of failures not shown to be extremely improbable. AC 25.629-1B also provides guidance for consideration of inadvertent encounters with icing for airplanes not certificated for flight in icing conditions, as required by § 25.629(d)(3). Flutter analyses should reflect all mass accumulations of ice on protected and unprotected surfaces from exposure to Appendix C and Appendix O conditions in accordance with the guidance in AC 25.629-1B. This includes any accretions that could develop on control surfaces.
8.5 Power Sources.
The applicant should evaluate the power sources in the IPS design (e.g., electrical, bleed air, and pneumatic sources). An electrical load analysis or test should be conducted on each power source to determine that it is adequate to operate the IPS as well as to supply all other essential electrical loads for the airplane throughout the airplane flight envelope. The effect of an IPS component failure on availability of power to other essential loads should be evaluated in accordance with § 25.1309. All power sources affecting engines or engine IPSs for multi-engine airplanes must comply with the engine isolation requirements of § 25.903(b).
8.6 Failure Analyses.
8.6.1 Failure Analysis for § 25.1419 (Appendix C Conditions).
AC 25.1309-1A, System Design Analysis, provides guidance for demonstrating compliance with § 25.1309. The hazard classifications of IPS failure conditions are typically substantiated with analyses and/or testing. A failure analysis should include the potential contribution of complex electronic hardware faults and malfunctions to system failure conditions. It should also classify the hardware assurance level appropriately, as outlined in RTCA DO-254, Design Assurance Guidance for Airborne Electronic Hardware. For purposes of a quantitative analysis, the probability of encountering Appendix C icing conditions is considered “1.”
8.6.2 Failure Analysis for § 25.1420 (Appendix O Conditions).
Applying the system safety principles of § 25.1309 is helpful in determining the need for system requirements to address potential hazards from an Appendix O icing environment. The following addresses application of the § 25.1309 principles to Appendix O conditions and may be used for showing compliance with § 25.1309.
8.6.2.1 Hazard Classification.
8.6.2.1.1 Assessing a hazard classification for compliance with § 25.1309 is typically a process combining quantitative and qualitative factors. If the design is new and novel and has little similarity to previous designs, a hazard classification based on past experience may not be appropriate. If the new design is derivative in nature, the assessment can consider the icing event history of similarly designed airplanes, and, if applicable, the icing event histories of all conventionally designed airplanes. The applicant should consider specific effects of supercooled large drop icing when assessing similarity to previous designs (see paragraph 12.1.4, Some Areas of Interest for Appendix O).
8.6.2.1.2 Qualitative analysis may be used to determine the hazard classification for an unannunciated encounter with Appendix O icing conditions. The analysis can be applied to airplanes shown to be similar to previous designs with respect to Appendix O icing effects, and to which the icing event histories of all conventionally designed airplanes are applicable. The following assumptions may be used to support the qualitative analysis:
8.6.2.1.2.1 The airplane is certificated to either detect Appendix O icing conditions and safely exit all icing after detection of Appendix O icing conditions, or safely operate in a selected portion of Appendix O icing conditions and safely exit all icing after detection of Appendix O icing conditions beyond those for which it is certificated.
8.6.2.1.2.2 The unannunciated encounter is with Appendix O icing conditions in which the airplane has not been shown to operate safely.
8.6.2.1.2.3 The airframe and propulsion IPSs have been activated prior to the unannunciated encounter.
8.6.2.1.3 The applicant may use service history, design, and installation appraisals to support hazard classifications for § 25.1309. Service history may be appropriate to support a hazard classification if a new or derivative airplane has similar design features to a previously certificated airplane.
8.6.2.1.4 While definitive statistics are not available, a historical perspective can provide some guidance. Many airplanes flying through icing have been exposed to supercooled large drop conditions without the pilot being aware of it. The interval of exposure to the supercooled large drop
17 conditions may have varied from a brief amount of time (such as could occur during a vertical transition through a cloud) to a more sustained exposure (such as during a hold). Severity of the exposure conditions in terms of water content may have varied significantly. Therefore, not all encounters with supercooled large drop conditions will result in a catastrophic event.
8.6.2.1.5 Icing event history of conventionally designed airplanes certificated before the introduction of § 25.1420. Given the volume of airplane operations and the number of reported incidents that did not result in a catastrophe, a factor of around 1 in 100 is a reasonable assumption of probability for a catastrophic event if an airplane encounters Appendix O conditions in which it has not been shown capable of safely operating. An applicant may assume that the hazard classification is severe major for an unannunciated encounter with Appendix O conditions while the IPS is activated, in accordance with AC 25.1309-1A, provided that both of the following are true: (1) the airplane is similar to previous designs with respect to Appendix O icing effects, and (2) the applicant can show that the icing event history of all conventionally designed airplanes is relevant to the airplane being considered for certification
8.6.2.1.6 If an airplane is not similar to a previous design, an assessment of the hazard classification may require more analysis or testing. One method of hazard assessment would be to consider effects of ice accumulations similar to those expected for airplanes being certified under § 25.1420.
Such ice shapes may be defined from a combination of analysis and icing tanker or icing wind tunnel testing. Aerodynamic effects of such shapes could be evaluated with wind tunnel testing or, potentially, CFD. See AC 20-73A for additional guidance on assessing aerodynamic effects of ice build-ups. Hazard classification typically takes place early in a certification program. Therefore, a conservative assessment may be required until sufficient supporting data is available to reduce the hazard classification.
8.6.2.2 Probability of Encountering Appendix O Conditions.
Appendix C was designed to include 99 percent of icing conditions.
Therefore, the probability of encountering icing outside of Appendix C drop conditions is on the order of 10-2. The applicant may assume that the average probability for encountering Appendix O icing conditions is 1 x 10-2 per flight hour. This probability should not be reduced based on phase of flight.
8.6.2.3 Numerical Safety Analysis.
For the purposes of a numerical safety analysis, the applicant may combine the probability of equipment failure with the probability, defined above, of encountering Appendix O icing conditions. If the applicant can support a hazard level of “hazardous,” using the above probability (10-2)
18 of encountering the specified supercooled large drop conditions, the probability of an unannunciated failure of the equipment that alerts the flightcrew to exit icing conditions should be less than 1 x 10-5.
8.6.2.4 Assessment of Visual Cues.
Typical system safety analyses do not address the probability of flightcrew actions, such as observing a visual cue before performing a specified action. As advised in AC 25.1309-1A, quantitative assessments of flightcrew errors are not considered feasible. When visual cues are to be the method for detecting Appendix O conditions and determining when to exit them, the applicant should assess the appropriateness and reasonableness of the specific cues (see paragraph 12.1.3.2 of this AC for additional guidance). Reasonable tasks are those for which the applicant can take full credit because the tasks can realistically be anticipated to be performed correctly when required. The applicant should assess the task of visually detecting Appendix O conditions to determine if it could be performed when required. The workload for visually detecting icing conditions should be considered in combination with the operational workload during applicable phases of flight. The applicant may assume that the flightcrew is already aware that the airplane has encountered icing.
The assessment of whether the task is appropriate and reasonable is limited to assessing the task of identifying Appendix O accumulations that require exiting from the icing conditions.
8.7 Similarity Analyses.
8.7.1 For certification based on similarity to other type-certificated airplanes previously approved for flight in icing conditions, the applicant should specify the airplane model and the component to which the reference of similarity applies. The applicant should show specific similarities in the areas of physical, functional, thermodynamic, pneumatic, and aerodynamic characteristics as well as in environmental exposure. The applicant should conduct analyses to show that component installation, operation, and effect on the airplane’s performance and handling are equivalent to that of the same or similar component in the previously approved configuration.
8.7.2 A demonstration of similarity requires an evaluation of both system and installation differences. Differences should be evaluated for their effect on IPS functionality and on safe flight in icing. If there is uncertainty about the effects of the differences, the applicant should conduct additional tests and/or analyses as necessary and appropriate to resolve the open issues.
8.7.3 Section 25.1419(b) requires flight testing in measured natural icing conditions. Flight test data from previous certification programs may be used to show compliance with § 25.1419(b) if the applicant can show that the data is applicable to the airplane in question. If there is uncertainty about the similarity analysis, the applicant should conduct flight tests in measured natural icing conditions for compliance with § 25.1419(b).
8.7.4 On derivative or new airplane designs, the applicant can use similarity to previous type designs shown to comply with § 25.1420 or airplanes that have shown compliance with § 25.1419 that have a successful service history, if the effects of differences are substantiated. Natural ice flight testing may not be necessary for a design shown to be similar. At a minimum, the following differences should be addressed:
• Airfoil size, shape, and angle of attack.
• IPS design.
• Operating altitude and airspeed.
• Center of gravity.
• Flight control system.
• Engine and propeller operation.
Note: The applicant must possess all the data to substantiate compliance with applicable regulations, including data from past certifications on which the similarity analysis is based.
8.8 Impingement Limit Analyses.
8.8.1 The applicant should prepare a drop trajectory and impingement analysis of—
• Wings,
• Horizontal and vertical stabilizers,
• Propellers, and
• All other critical surfaces on which ice may accrete.
8.8.2 This analysis should consider the various airplane operational configurations, phases of flight, and associated angles of attack. The analysis should establish upper and lower aft drop impingement limits that can then be used to establish the aft ice formation limit and its relationship to the IPS coverage.
8.9 Ice Shedding Analyses.
8.9.1 Airframe ice shedding may damage or erode engine or powerplant components as well as lifting, stabilizing, and flight control surface leading edges. Fan and compressor blades, impeller vanes, inlet screens and ducts, and propellers are examples of powerplant components subject to damage from shedding ice. For fuselage-mounted turbojet engines (and pusher propellers that are very close to the fuselage and well aft of the airplane’s nose), ice shedding from the forward fuselage and from the wings may cause significant damage. Ice shedding from components of the airplane, including antennas, should not cause damage to engines and propellers that would adversely affect engine operation or cause serious loss of power or thrust (compliance with § 25.1093). The applicant should also consider airplane damage that can be caused by ice shedding from the propellers.