(4) Develop procedures and limitations for the use of the ice protection system in normal, abnormal, and emergency conditions.
b. Flight tests are generally conducted in three stages:
(1) Initial dry air tests with ice protection equipment installed and operating;
(2) Dry air tests with predicted artificial ice shapes installed; and
(3) Flight tests in icing conditions, including simulated icing tests.
(a) Initial dry air tests are usually the first steps conducted to extend the basic airplane certification to evaluate the airplane with the ice protection system installed and operating. The initial dry air tests are conducted to verify that the ice protection system does not affect the flying qualities of the basic airplane in clear air. Often, it is more economical to verify specific analyses by ground tests where the design variables can be controlled to some extent. Flight tests in icing conditions, including flight behind airborne icing tanker aircraft, are normally employed to demonstrate that the ice protection system performs under flight conditions as the analysis or ground test indicated. These demonstrations should be made at various points (targeting critical points) in the icing envelope of part 25, Appendix C, to verify the airplane's ability to safely operate throughout that icing envelope.
11. FLIGHT TESTS. The following sections cover the major flight tests and/or analyses normally performed to substantiate the flight aspects of an ice protection system:
a. Initial Dry Air Tests with Ice Protection Equipment Installed. Depending upon the detailed design of the ice protection system, some preliminary ground tests of the equipment may be warranted to verify the basic function of each item. Quantitative data on such items as temperatures of thermal devices, fluid flow rates and flow patterns on liquid devices, or operating pressures of pneumatic components may be obtained as necessary to verify the system designs.
/g183/g32 The airplane should be shown to comply with the certification requirements when all ice protection system components are installed and functioning. This can normally be accomplished by performing tests at those conditions found to be most critical to basic airplane aerodynamics, ice protection system design, and powerplant functions.
Pneumatic boots and all other anti-ice/deice equipment should operate throughout the entire flight envelope to demonstrate that no damage occurs. Section 23.1419 requires that the adequacy of the airplane's ice protection system be established based on operational needs. Tests must be conducted to demonstrate that the airplane is capable of operating safely in Continuous Maximum and Intermittent Maximum icing conditions as described in Appendix C of part 25. Several commonly used ice protection system components are discussed below to illustrate typical flight test 13
practices. Other types of equipment should be evaluated as their specific design dictates.
(1) Pneumatic Leading Edge Boots. Boot inflation rate and inflated boot shape are important parameters in ice accretion removal. Tests should demonstrate a rapid rise and decrease in operating pressures for effective ice removal. This pressure rise time, as well as the maximum operating pressure for each boot, should be evaluated throughout the altitude band of part 25, Appendix C—mean sea level (MSL) to 22,000 feet above MSL— unless performance constraints in the AFM restrict the airplane to a lesser altitude range.
Boots should be operated in flight at the minimum envelope temperature (-22 /g176F) of part 25, Appendix C, to demonstrate adequate inflation/deflation and throughout the entire flight envelope to demonstrate that no damage occurs. The appropriate speed and temperature (if any) limitation on activation of boots should be included in the AFM.
(a) The operation of the boots (inflation) should have no hazardous affect on airplane performance and handling qualities. An example of an unacceptable hazardous effect is that some boot inflation sequencing schemes result in abnormal pitch attitude changes. If there are anomalous pitch changes in any configuration, appropriate information or limitation should be in the AFM. This can be shown by inflating the boots at several speeds in the flight envelope from stall speed to (VNE + VD)/2 or (VMO + VD)/2 and observing the reaction of the airplane. This test can be hazardous and should be approached in a build-up manner by inflating the boots at incremental airspeeds starting from the middle of the flight envelope.
(b) Section 23.1309(b)(3) states that warning information must be provided to alert the crew to unsafe system operating conditions, and to enable them to take appropriate corrective action. Systems, controls, and associated monitoring and warning means must be designed to minimize crew errors, which could create additional hazards.
Section 23.1416(c) requires “that means to indicate to the flight crew that the pneumatic deicer boots system is receiving adequate pressure and is functioning normally must be provided.” Stall speed can increase dramatically with inflated boots and failures in the vacuum system need to be addressed.
(c) If the indicating lights for the pneumatic deicing system (boots) illuminate at a lower pressure than required for proper boot operation, misleading information is furnished to the flight crew, which can, in turn, lead to an unsafe operation. This could mislead the crew to believe the boots are operating normally when, in fact, the boots might not be inflating sufficiently to shed ice. Consideration should be given to the potential for accumulation of liquid water in the pneumatic deicing boots, which could freeze within the system and prevent proper operation. The pneumatic and boot arrangement should be examined for low points, which may collect water, and consideration should be given to the installation of water drainage points. Periodic inspection and drainage procedure instructions should be provided in the appropriate manual. Similarly, placement of the pressure sensor(s) should be evaluated to prevent misleading boot inflation indications. An evaluation of the effectiveness of water/air 14
separators and/or drainage holes should be accomplished by flying through precipitation followed by a demonstration of system operation at freezing altitudes.
(2) Electric Propeller Boots. When flying in dry air, the systems should be monitored to confirm proper function. It is suggested that system current, brush block voltage (between each input brush and the ground brush), and system duty-cycles be monitored to ensure that proper power is applied to the deicers. If not furnished by the manufacturer, surface temperature measurements may be made during dry air tests.
These surface temperature measurements are useful for correlating analytically predicted dry air temperatures with measured temperatures or as a general indicator that the system is functioning and that each deicer is heating.
(a) The system operation should be checked throughout the full r.p.m. and propeller cyclic pitch range expected during icing flights. Any significant vibrations should be investigated. Consideration should be given to the maximum temperatures that a composite propeller blade may be subjected to when the deicers are energized. It may be useful to monitor deicer bond-side temperatures. When performing this evaluation, the most critical conditions should be investigated (for example, this may occur on the ground (propellers non-rotating) on a hot day with the system inadvertently energized).
(b) The system should be monitored to confirm proper function in precipitation.
There have been designs that allowed water to reach the brush blocks and prevent their operation.
(3) Electric Windshield Anti-Ice. Dry air flight tests should be conducted in support of the systems design, as required. Inner and outer windshield surface temperature evaluations of the protected area may be needed to support thermal analyses.
Thermal analysis should substantiate that the surface temperature is sufficient to maintain anti-icing capability without causing structural damage to the windshield. In the case of add-on plates, temperatures of the basic airplane windshield, inside and out, may also be needed, particularly with pressurized airplanes.
(a) An evaluation of the visibility, including distortion effects through the protected area, should be made in both day and night operations. In addition, the size and location of the protected area should be reviewed for adequate visibility, especially for approach and landing conditions. Crosswinds and runway light visibility during instrument landings need to be considered. A probable single failure of a transparency heating system should not adversely affect the integrity of the airplane cabin or create a potential danger of fire.
(4) Pitot-Static and Static Pressure Sources. If the aerodynamic configuration of either the pitot or the static source(s) differs from that of the basic airplane, then airspeed and altimeter system calibrations should be evaluated for compliance with the certification requirements. A component surface temperature evaluation may be necessary to verify thermal analyses. Section 23.1325(b) requires that static pressure port 15
design or location should be such that the correlation between air pressure in the static pressure system and true ambient atmospheric static pressure is not altered when the airplane encounters icing conditions. Section 23.1325(b)(3) allows an anti-icing means or an alternate source of static pressure may be used in showing compliance with the requirement.
(5) Stall Warning and Angle-of-Attack Sensors. Ice could form on these sensors if these devices are not protected. When the icing approval requires installation of new or modified sensors, that sensor's function should be evaluated for compliance with the certification requirements. These sensors may not require heat for ice protection if substantiated by analyses. A surface temperature evaluation may be necessary to verify thermal analyses. Consideration should be given to ice formations on the airframe in the vicinity of the sensor mounting location that may affect the sensor’s operation. Natural icing flight tests should include a demonstration of proper stall warning operation.
(6) Pitot Tube. Section 23.1323 requires a heated pitot tube or an equivalent means of preventing malfunction due to icing. Section 23.1326 requires a pitot tube heat indicating system if a flight instrument pitot heating system is installed to meet ice protection requirements.
(7) Fluid Anti/Deice Systems. Dry air testing should include evaluation of fluid flow paths to determine that adequate and uniform fluid distribution over the protected surfaces is achieved. Means of indicating fluid flow rates, quantity remaining, and so forth, should be evaluated to determine that the indicators are plainly visible to the pilot and that the indications provided can be effectively read. An accessible shutoff should be provided in systems using flammable fluids. The fluid anti-ice/deice systems may be used to protect propellers and windshields, as well as leading edges of airfoils. The fluid for windshield fluid anti-ice systems should be tested to demonstrate that it does not become opaque at low temperature.
(8) Compressor Bleed Air Systems. The effect of any bleed air extraction on engine and airplane performance should be examined and shown in the AFM performance data. The surface heat distribution analysis should be verified for varying flight conditions including climb, cruise, hold, and descent. A temperature evaluation may be necessary to verify the thermal analyses. If compressor bleed air is used for antiicing an engine cowl that is made of composite material, a thermal analysis/survey should be conducted to ensure there is no engine cowl delamination.
(9) Ice Detection Light(s). Ice detection lights may be necessary if operations are dependent upon observing ice accumulations at night (§ 23.1419(d)). Ice detection lights should be evaluated both in and out of clouds during night flight to determine that adequate illumination of the component of interest is available without excessive glare, reflections or other distractions to the flight crew. These tests may be conveniently accomplished both in and out of clouds during dry air tests. Use of a hand-held flashlight for ice detection is not acceptable. As described in § 23.1419(d), “The Airplane Flight 16
Manual or other approved manual material must describe the means of determining ice formation and must contain information for the safe operation of the airplane in icing conditions.”
b. Dry Air Tests with Artificial Ice Shapes. The installation of artificial ice shapes allows airplane performance and handling characteristics to be evaluated in stable dry air conditions with the critical ice shape being held constant (no change of ice accretion due to erosion, shedding, and so forth, that can occur with natural ice shapes). Dry air flight tests with artificial ice shapes installed also result in a considerable reduction in the amount of flight testing that would otherwise be required to accumulate the test ice shapes, and then evaluate their effects on airplane performance and handling characteristics in stable air. Dry air tests with artificial ice shapes can be hazardous if not approached safely; therefore, the dry air flight test evaluation should be performed using a build-up technique, considering increases in spanwise coverage and dimensions of artificial ice shapes prior to full span ice shape tests.
(1) The shape and texture of artificial ice shapes should be developed and substantiated using methods found acceptable to the FAA. Common practices include:
use of computer codes, flight in measured natural icing conditions, icing wind tunnel tests, and flight in a controlled simulated icing cloud (for example: behind an airborne icing tanker). The validity of the ice shape predictions from analytical computations, simulated icing flight tests or icing tunnel tests should be confirmed by flight tests in natural icing. These predictive methods should be conservative and should address the conditions associated with the icing envelope of part 25, Appendix C, that are critical to the airplane's performance and handling qualities in critical phases of the airplane's operational envelope, including climb, cruise, descent, holding pattern, approach, and landing.
(2) Considerations should be given to the type of ice protection systems (for example: mechanical, fluid, thermal, or hybrid) to the most adverse ice conditions (shape or shapes, texture, location, and thickness) for the relevant aerodynamic characteristics for the following, where appropriate: delayed turn on; intercycle conditions; failure conditions; and residual ice. See Paragraph 11d.
(3) For aircraft that have an ice detection system, consideration must be given to delays in ice detection. These delays include slow ice detector response at temperatures near freezing (temperatures above the Ludlam Limit as discussed in AC 20-73) and the number of probe heat cycles utilized for annunciation or automatic ice protection activation.
(4) The effect of the ice shapes on stall speeds and airplane climb performance should be determined. Stall warning margins and maneuvering capability should also be evaluated. Operating speeds, stall warning speeds, and AFM performance information should be adjusted, if necessary, to provide acceptable performance capability and stall warning margins. The computation of the effects of ice on AFM performance should 17
include the loss of engine power or thrust resulting from the applicable operating mode of the ice protection system.
(5) Handling characteristics are expected to degrade in icing conditions and should be investigated to determine that the “airplane is capable of operating safely.” For certification bases before Amendment 23-43, Subpart B requirements are used as guidelines. For certification bases at Amendment 23-43 and higher, several Subpart B requirements also apply in icing conditions. This is addressed in paragraph 11.d. The results of these tests may be used in preparing specific AFM operating procedures and limitations for flight in icing conditions.
c. Flight Tests in Icing Conditions. Flight tests in measured natural icing and the use of simulated icing tools such as icing tankers and icing wind tunnels are normally employed to demonstrate that the ice protection system performs under flight conditions as the analysis or other tests indicate. They are also used to confirm the analyses used in developing the various components (for example, ice detectors) and ice shapes and, in the case of natural icing tests, to confirm the conclusions reached in flight tests conducted with artificial ice shapes. Testing should be accomplished at various points in the icing envelope of part 25, Appendix C, to verify the airplane's ability to safely operate throughout that icing envelope.
(1) Instrumentation. Sufficient instrumentation should be planned to allow documentation of important airplane, system and component parameters, and icing conditions encountered. The following parameters should be considered:
(a) Altitude, airspeed, and engine power.
(b) Static air temperature, engine component temperatures (for example, oil, heat exchanger fluids, cylinder head), electrical generation equipment temperatures, surface temperatures, interlaminate temperatures, and any other key temperatures that could be affected by ice protection equipment, by ice accumulation or other key temperatures that are necessary for validation of analyses.
(c) Liquid water content can be measured using a hot-wire anemometer based instrument, calibrated drum, or other equivalent means.
(d) Median volumetric droplet diameter can be approximately determined by using a drop snatcher to expose a gelatin oil or soot slide and then measuring the resultant impact craters, or by use of more sophisticated equipment such as a laser based droplet measuring and recording instrument.
Note 1: The FAA Aircraft Icing Handbook, DOT/FAA/CT-88/8, defines median volumetric diameter the same as mean effective diameter, the difference being the former is measured while the latter is calculated assuming a drop size distribution.
(e) Cameras and reference aids to assist in determining ice accretion thickness and ice accretion coverage.
(2) Simulated Icing. Testing in simulated icing environments such as icing tunnels or behind airborne icing tankers represents one way to predict the ice protection capabilities of individual elements of the ice protection equipment. Due to the limited volume of the simulated icing environment, testing is usually limited to components having small exposed surfaces such as heated pitot tubes, antennas, air inlets including engine induction air inlets, empennage, and other surfaces having small leading edge radii and windshields. Small components are more sensitive to the higher accumulation rates associated with high liquid water content and large droplet size. These conditions are easily simulated and not frequently encountered in natural icing flight tests.
/g183/g32 A simulated icing exposure may be obtained by the use of onboard spray nozzles forward of the component under examination or by flying the test airplane in the cloud generated by an airborne icing tanker. Simulated icing clouds should be measured to ascertain that they contain the required cloud metrics (droplet sizes, liquid water content, temperature, and so forth) and accretions from these clouds can be used to show compliance with icing criteria. For those components where small droplet sizes are critical, simulated icing tests should be evaluated to ensure the conditions of concern are accurately simulated.
/g183/g32 Icing tunnel tests have been accepted for definition of pre-activation, intercycle, residual, and runback ice on protected surfaces with the following considerations:
(a) A full-scale test article is preferable due to uncertainties in ice accretion scaling. To date the FAA has not accepted data on scaled models because of the uncertainties involved in the scaling laws.
(b) The test article must be conformed. Although parts of the ice protection system may be simulated, critical system parameters must be conformed. An example would be deicing boot steady state pressure, and pressure rise time and decay time.
(c) Ice protection system tolerances on the production airplane, such as boot operating pressure, must be accounted for.
(d) Proposed ice protection system operation (activation procedures, ice detection system delay, deicing boot cycle times) must be accounted for in the test matrix.
(e) Spray times can be adjusted for part 25, Appendix C cloud lengths. The test matrix should include longer times in Continuous Maximum conditions to evaluate the stability and cyclic nature of intercycle and residual ice. Certain unique design features, 19
such as stall strips mounted on deicing boots, may not readily shed ice and spray times up to 45 minutes need to be evaluated.
(f) An outboard section is usually tested since it is typically more critical for aerodynamic degradations due to the reduced scale relative to the wing root (on wings incorporating significant taper ratios). It will also have higher water collection efficiency and may operate at a lower angle of attack, thereby promoting greater aft impingement of droplets on the suction surface. For thermal systems, the outboard sections also represent the extremities of the bleed air system where temperature and pressure losses are the greatest which can be critical for runback accretions. The distribution of icing cloud parameters along the test span should be taken into account.
(3) Natural Icing. Flight tests in natural icing conditions are necessary to demonstrate the acceptability of the airplane and ice protection system for flight in icing conditions. AC 20-73 (Items 25f and 25g(1)) provides additional information that would be useful when establishing a natural icing flight test program. At least one exposure to icing conditions within the part 25, Appendix C, Continuous Maximum envelope should be obtained. The exposure should be sufficiently stabilized to obtain valid data. It is often difficult to obtain temperature stabilization in brief exposures. Additional exposures may be required to allow extrapolation to the envelope critical conditions by analysis. Test data obtained during these exposures may be used to validate the analytical methods used and the results of any preceding simulated icing tests.
/g183/g32 Past experience has shown that flight testing in natural Intermittent Maximum icing conditions may be hazardous due to accompanying severe turbulence and possible hail encounters that may extensively damage the test airplane. When design analyses show that the critical ice protection design points (that is, heat loads, critical shapes, accumulation, and accumulation rates, and so forth) are adequate under these conditions, and sufficient ground or flight test data exists to verify the analysis, then hazardous flight testing should be avoided.
/g183/g32 During natural icing flight tests, ice accumulation on unprotected areas should be observed and documented. Remotely located cameras either on the test airplane or on a chase airplane have been used to document ice accumulations on areas that cannot be seen from the test airplane’s flight deck or cabin. Visual devices such as rods and/or paint stripes may be used to aid in visual analysis of ice accretions. The edges of paint stripes can be efficient ice collectors if not smoothed and must be accounted for.
/g183/g32 The location of all external instrumentation installed for icing flight tests, including cameras and visual devices, should be analyzed to verify that ice-shedding hazards are not introduced.
/g183/g32 Sufficient data should be taken to allow correlation with dry air tests using artificial ice shapes. This should be accomplished with a target accretion thickness equivalent to the 45-minute dry air ice shapes on an unprotected part of the wing. Handling qualities and performance should be subjectively reviewed and determined to be in general correlation with those found in dry air testing. For certification bases at Amendment 23-43 or higher, refer to Paragraph 11.d. for performance, stability, control and maneuverability requirements.
/g183/g32 In addition, flying qualities and performance should be qualitatively evaluated with the ice accumulations existing just prior to operation of deice (as opposed to anti-ice) components. The ice protection systems are to be activated by the flight crew in accordance with approved AFM procedures when icing conditions exist; however, for anti-ice components, tests should be conducted that simulate inadvertent icing encounters in which the pilot may not recognize that the airplane is about to enter an icing condition and the anti-ice component may not be activated until actual ice buildup is noticed.
/g183/g32 A delayed ice accumulation event of 30 seconds to 2 minutes has been used in these tests to simulate the flight crew's failure to recognize an icing condition. For the delayed ice accumulation time event, consideration should be given to the icing conditions, the icing recognition means available, recommended crew procedures, and ice protection system performance of the particular aircraft. Handling qualities should remain acceptable to the test pilot and the airplane should be capable of operating safely.
/g183/g32 All systems and components of the basic airplane should continue to function as intended when operating in an icing environment. Some considerations are:
(a) Engine and equipment such as generator under maximum ice protection load cooling should be monitored during icing tests and be found acceptable for this operation.
(b) Engine alternate induction air sources should remain functional in an icing environment.
(c) Fuel system venting should not be affected by ice accumulation.
(d) Retractable landing gear should be available for landing following an icing encounter. Gear retraction should not result in an unsafe indication because of ice accretion.
(e) Ice shedding from components including antennas of the airplane should cause no more than cosmetic damage to other parts of the airplane, including aft-mounted engines and propellers.
(f) With pre-activation, intercycle, or residual ice accumulations on the airplane, acceptable stall warning (aerodynamic or artificial) and stall protection system, if installed, should be provided. The stall warning should meet the requirements of § 23.207(a), (b), and (c). The type of stall warning in icing conditions should be the same as in no icing conditions. Biasing of the stall warning and stall protection system, if installed, may be required to achieve acceptable margins to stall. The maneuver margin requirements § 23.207(d) should be demonstrated in icing conditions.
Note 2: This test and any handling qualities tests in natural icing should be accomplished in VFR conditions for safety.
(g) Ice detection cues that the pilot relies on for timely operation of ice protection equipment should be evaluated in anticipated flight attitudes.
(h) Ice detection lights should be evaluated in natural icing night conditions to verify that they illuminate ice build-up areas, are adequate under the conditions encountered, and do not introduce objectionable glare.
(i) Primary and secondary flight control surfaces should remain operational after exposure to icing conditions. Demonstrate that aerodynamic balance surfaces are not subject to icing throughout the airplane's operating envelope (weight, center of gravity, and speed), or that any ice accumulation on these surfaces does not interfere with or limit actuation of the control for these surfaces including retraction of flaps for a safe go around from the landing configuration.
(j) Ice accretions forward of pitot probes and static sources, such as accretions on radomes or other probes, should not affect the position error of the aircraft’s production air data system.
(k) All autopilot modes should function properly in icing conditions. Airframe leading edge ice accretions could affect control power and control hinge moments resulting in incorrect autopilot gains. These evaluations should also show that autopilot actuators function properly and do not freeze up. The autopilot should be engaged for an extended period of time in natural icing conditions to check for unusual trimming and potential for ice to accrete in control surface gaps “control surface ice bridging.”
(l) For the determination or validation of intercycle and residual ice shapes and roughness on deicing boots, the application of any ice adhesion inhibitor such as ICEX is not permitted for natural icing flight tests, simulated icing flight tests or icing tunnel tests.
This is because the use of ICEX cannot be controlled in operations and the effectiveness in operations degrades over time. (Intercycle ice is the ice accretion that exists on a deicing system surface just prior to an actuation of the deicing system; residual ice is the accretion remaining immediately after an actuation.) Other products that enhance appearance or life should also not be applied. Deicing boots can be cleaned at the start of a natural icing program per recommended maintenance procedures.
d. Performance and Handling Qualities – § 23.1419 at Amendment 23-14 or earlier. Airplane performance and handling qualities are degraded by ice accumulations in various ways depending upon type, shape, size, and location of these accumulations.
Because of these variations in degradation, it is difficult to establish a standard method of demonstrating such degradations. However, certain minimum tests, as suggested below, should be used to demonstrate that the airplane does not have unsafe features or characteristics that prevent it from being capable of operating safely in part 25, Appendix C, icing envelope. If numerous unprotected areas exist, the weight and center of gravity effects of the ice formations should also be evaluated.
/g183/g32 The FAA and the Joint Aviation Authorities (JAA) are harmonizing the performance and handling qualities of part 25. The Aviation Rulemaking Advisory Committee (ARAC) Flight Test Harmonization Working Group will complete the harmonization project to standardize performance, handling requirements, and additional guidance material for certification of part 25/Joint Aviation Requirements 25 (JAR 25) airplanes to safely operate in the icing conditions of Appendix C. These performance and handling qualities issues will be considered for part 23 requirements and guidance information (future rulemaking and ACs that are being publicized by the ARAC) where appropriate.
(1) Performance. For normal, utility, and acrobatic category airplanes, performance losses are normally demonstrated in icing conditions only for the all engines operating condition. For commuter category airplanes, however, which have takeoff and landing weight limitations based on one engine inoperative climb performance, testing for one engine inoperative performance loss is appropriate. Climb performance losses should be established either by flight tests or by a conservative analysis acceptable to the FAA certifying office. Artificial ice shapes used for performance evaluation should be those critical shapes as found under the conditions in the icing envelope of part 25, Appendix C, and determined for the critical operating conditions under which such performance is expected. The following performance loss determinations are normally considered minimum:
(a) Section 23.65, Climb: All engines operating. Climb performance losses due to ice formation for the configuration defined in § 23.65 are normally not appropriate below 400 feet since the airplane should not depart with ice on the airplane.
Takeoff climb performance should be determined considering any losses associated with operating anti-ice/deice equipment since that equipment could be utilized for takeoff into an icing environment. Ice accretion during takeoff needs to be accounted for on airplanes that turn off the airframe ice protection to minimize bleed/power extractions. It should be assumed no flightcrew action to activate the ice protection will occur until at least 400 feet above ground level, or higher if an AFM procedure allows.
(b) Section 23.67(b) and (c), Climb: one engine inoperative. Climb performance losses should consider related power extractions, additional icing drag, and any required changes to operational climb speeds for at least the following:
1. One engine inoperative takeoffs to 400 feet are conducted without ice, above 400 feet ice accretion should be considered;
2. Climb with one engine inoperative in the en route configuration; and
3. Climb with one engine inoperative in the approach configuration.
/g183/g32 Ice accretion during takeoff needs to be accounted for on airplanes that turn off the airframe ice protection to minimize bleed/power extractions. It should be assumed no flightcrew action to activate the ice protection will occur until at least 400 feet above ground level, or higher if an AFM procedure allows.
(c) Section 23.75, Landing. The landing performance should be calculated or measured considering the effects of critical ice accumulations upon landing. Minimum speeds, landing configuration, and landing distance (based on increased stall speeds) degradation should be established.
(d) Section 23.77, Balked landing. For normal, utility, and acrobatic category airplanes, the airplane with ice accumulations and all icing systems operational (for example, bleed air systems) should meet the all engine minimum climb requirements on a 32 /g176F day at sea level as is required for the non-iced (icing systems off) airplane under § 23.77(a) at sea level on a standard day. For commuter category airplanes, climb performance losses should be measured and the maximum weight adjusted, if required.
(e) Propeller Efficiency. To date, climb performance analyses and climb flight testing with ice shapes have not taken into account propeller efficiency losses due to ice accretion on the propeller blades. Deicing boot manufacturers analyses show that residual ice does exist with propeller deicing systems and their analyses do not account for ice runback. The outer part of the blade, which normally is not protected, theoretically has sufficient centrifugal force to shed ice. Stop frame video of recent flight testing of a part 23 aircraft in Supercooled Large Droplet (SLD) conditions have shown ice accretions on the full span of the propeller blades.
Although this condition was outside of 14 CFR part 25, Appendix C, there is a possibility that this may occur within some portions of Appendix C. Airplane performance during natural icing flight testing should be qualitatively compared with performance during ice shape flight tests. On reciprocating and turboprop powered airplanes, if there is degradation in performance compared to the ice shape results, propeller efficiency losses due to propeller ice accretions should be investigated.