b. Normally, the IPS components are instrumented to measure the heat energy distributed to the heated surfaces and the temperature of the heated surfaces. You can use these measurements to validate your IPS thermal analyses by comparing the predicted with the measured parameters.
The test ambient temperature and altitude should cover the temperature-altitude envelope limits of 14 CFR part 25, Appendix C and 14 CFR part 29, Appendix C for fixed-wing and rotary-wing aircraft, respectively. You can use measured dry-air surface temperatures to determine the maximum possible surface temperatures and heat transfer characteristics. You can also use the measured surface temperatures to evaluate the adequacy of the heat source. You may use dry air testing to verify that the temperatures measured on the IPS component surfaces are within those allowed for the structure.
8.2.2.2 Compliance Means: Dry Air Flight Test Pneumatic Ice Protection Systems. For aircraft designs using pneumatic deicing boots, applicants should perform tests to demonstrate the pneumatic characteristics of the IPS. This includes the deicing boots’ inflation and deflation pressure rates and the inflated dwell intervals and pressures. You should evaluate these inflation and deflation rates and air pressures throughout the altitude range defined in 14 CFR part 25, Appendix C and 14 CFR part 29, Appendix C, and the aircraft and IPS performance envelopes.
The deicing boots must operate effectively within the Continuous Maximum and Continuous Intermittent Envelopes of 14 CFR part 25, Appendix C and 14 CFR part 29, Appendix C.
Cycling of the pneumatic IPS should have no hazardous effect on the aircraft’s performance and handling qualities. Operate the pneumatic IPS in flight at the coldest temperature (-22°F) required by 14 CFR part 25, Appendix C and 14 CFR part 29, Appendix C, Continuous Maximum Icing Conditions. Cycling of the boots at the coldest temperature should show acceptable boot performance and that no damage occurs to the boots. Include all airspeed and temperature limitations on use of the deicing boots in the Limitation Section of the AFM. For transport category airplanes, you must show acceptable IPS alerts and cautions required by 14 CFR § 25.1419(c) during dry air testing. For transport category rotorcraft, 14 CFR § 29.1419(e) requires a means be provided to identify or determine the formation of ice on critical parts of the aircraft.
8.2.2.3 Compliance Means: Dry Air Flight Test Propeller Thermal Ice Protection Systems Evaluation.
a. For propulsion systems that include propeller thermal IPSs, applicants may perform dryair flight-tests to show compliance with 14 CFR § 23.903(c) and 14 CFR §§ 25.901(c),
25.903(b), and 25.1419(c).
b. You may perform initial evaluations of the electrothermal IPS power requirements at critical propeller operating and icing conditions during dry air testing. You may accomplish this evaluation by using suitable instrumentation to measure the electrical power consumed.
c. During dry air flight tests, you should monitor various propeller IPS parameters to confirm proper operation of the IPS. Also, monitor the IPS current, brush block voltage between each input brush and the ground brush, and IPS duty cycles to ensure that the IPS power remains within limits.
d. You should check the propeller IPS operation throughout the propeller’s expected revolutions per minute (rpm) and cyclic pitch ranges during flight in icing conditions. You should investigate and correct all vibrations deemed unacceptable.
8.2.2.4 Compliance Means: Dry Air Flight Test Windshield Ice Protection Evaluation.
Airframe type certificate applicants should conduct dry-air flight tests to verify thermal analyses used to show compliance with 14 CFR §§ 23.775(f), 25.773(b)(1)(ii), and 29.773(b)(1)(ii). You may need to measure the inner and outer windshield surface temperatures to verify your thermal analysis. With the windshield IPS on, you should evaluate the visibility, including distortions through the protected windshield area, for both day and night operations. Also, evaluate the size and location of the protected area for adequate visibility during the approach and landing phases of flight. (See appendix L of this AC.)
8.2.2.5 Compliance Means: Dry Air Flight Test Air-data Instrumentation Ice Protection Evaluation. Applicants should measure the surface temperature of air-data instruments (for example, pitot tubes, pitot-static pressure probes, and angle-of-attack probes (if ice protected)) during dry air flight tests or icing wind tunnel tests to verify thermal analyses used to show compliance with 14 CFR §§ 23.1323(d), 23.1325(b)(3), 25.1323(i), 25.1325(b), 27.1325(b), and
29.1325(c). You should evaluate the acceptability of the air data instruments’ ice protection during natural or simulated icing tests. You must also ensure the acceptability of an indication system for alerting the flight crew when the pitot tube IPS is not heated. (See 14 CFR §§ 23.1326(b)(1)(and (2) and 25.1326(b) (1) and (2).) An acceptable indication system may consist of separate lights or crew alert signals on an electronic display for each pitot source.
Further guidance on acceptable means of compliance is in AC 23-17A and AC 25-11.
8.2.2.6 Compliance Means: Dry Air Flight Test Safe-flight Evaluation with Simulated Ice Shapes.
a. Airframe type certificate applicants may flight test their aircraft with simulated ice shapes to show safe aircraft performance and handling qualities during flight into icing conditions. (See section 6.3 of this AC.) Using simulated ice shapes will allow you to evaluate the aircraft’s flying qualities in stable, dry air. It also allows you to evaluate the flying qualities without melting, sublimation, shedding, and erosion of ice buildups, as would occur with natural ice accretions. Also, dry-air flight testing of aircraft with simulated ice shapes facilitates demonstration of compliance with the required regulations and results in significant decreases in flight test costs, compared to flight testing in natural icing conditions.
b. You should develop and substantiate the simulated ice shape and surface texture using methods acceptable to the FAA. Use conservative methods, and address 14 CFR part 25, Appendix C and 14 CFR part 29, Appendix C icing conditions. The ice shapes and texture should represent those for the critical conditions for the flight characteristic and phase of flight under investigation. Alternatively, you can select a single, most critical ice shape and texture for all flight characteristics and phases of flight. Consider ice shapes and textures that form on protected and unprotected aircraft surfaces during the different phases of flight, including a 45-minute destination hold for your airplane.
c. You should determine the effect of the 45-minute hold in continuous maximum icing conditions of 14 CFR part 25, Appendix C. You should assume the airplane remains in a rectangular “racetrack” pattern, with all turns made within the icing cloud. Therefore, you should not use a horizontal extent correction for this analysis. You should also consider ice buildups that may form on protected surfaces before the ice protection system becomes fully effective after activation and during normal operation of the protection system. For example, consider the intercycle ice roughness on deicing IPS surfaces. If the failure analysis required by 14 CFR §§ 23.1309, 25.1309, 27.1309, and 29.1309 shows the need for continued safe flight following a failure in the IPS, such as for a portion of a wing or horizontal stabilizer, flight test the ice shape that results from the critical IPS failure to show the required performance and handling qualities are acceptable.
d. Appendix R of this AC provides information on how to determine ice shapes and textures of protected and unprotected surfaces and how to select critical ice shapes.
e. Information about testing methods and procedures may be found in AC 23-8B, AC 23.1419-2C, AC 25.1419-1A, AC 27-1B, and AC 29-2C.
f. You should conduct flight tests in measured natural icing conditions to evaluate the adequacy of simulated ice shapes used during dry air testing. Icing conditions that result in the simulated critical ice shape may not occur during natural icing testing. Also, the selected critical ice shape may be a composite of different ice features resulting in conservative degradation of performance and handling qualities for several phases of flight, and may not be a shape that would occur during natural icing. Therefore, effects of the simulated ice shapes during testing should be acceptably similar to that of natural ice shapes to provide assurance that the simulated ice shapes are conservative and properly derived. The corroboration should include confirmation that surfaces predicted to be free of ice, do in fact, remain ice-free. Guidance for determining the adequacy of the ice shapes is in appendix R of this AC.
g. Evaluations of performance and handling qualities results with natural ice accretions should be similar to the aircraft’s flying qualities with simulated ice shapes. Dissimilarity of results between the natural and simulated ice shape testing may require reevaluation of the simulated ice shapes and retesting, or added testing in natural icing conditions.
h. You should evaluate the effects of ice buildups on unprotected surfaces, such as on the radome or fuselage nose, and on air data system measurements, such as pitot and static pressures, angle-of-attack, stall warning, and airflow conditions. No adverse effects on the air data system measurements should occur. You may perform this evaluation using simulated ice shapes.
Record and correct all adverse air data system effects that occur during natural icing tests.
i. You must adjust the aircraft’s operating speeds, stall protection system activation schedules, and performance and operating procedures and limits to ensure compliance with the requirements discussed in section 6 of this AC. You should consider thrust losses resulting from the use of engine bleed air for ice protection and from reduced propeller efficiency caused by ice buildups on the propeller blades. Provide this information in the AFM.
j. You should approach simulated-ice-shape flight testing with extreme caution. Pre-flight analyses and flight test planning should result in a safe buildup to the full simulated-ice configuration.
8.2.2.7 Compliance Means: Dry Air Flight Test Ice-Contaminated Tailplane Stall (ICTS).
Ice accretion on the horizontal stabilizer may cause early airflow separation over the lower horizontal stabilizer surface, resulting in loss of airplane pitch control, loss of elevator authority, and pitch control force anomalies (reversed control forces and high upset recovery control forces). Adverse airplane pitch control and stability resulting from the reduced horizontal stabilizer stall angle (caused by the ice contamination) may occur during airplane configuration changes, such as when wing flaps are extended. This may also occur when engine power settings are changed and during changes in the airspeed. Airframe type certificate applicants should investigate ice-contaminated tailplane stall (ICTS) for all airplane designs, including those with powered controls. Applicants should determine whether this condition is likely to occur, resulting in an unsafe flight operation. Airplanes susceptible to ICTS are those having a near zero or negative tailplane stall margin. This evaluation typically is performed using simulated ice shapes along the leading edge of the horizontal stabilizer. An acceptable flight test procedure for determining susceptibility to ICTS is in AC 25-7A and AC 23.143-1. Appendix S of this AC provides guidance on ice-contaminated horizontal stabilizer stall.
8.2.3 Compliance Means: Simulated Icing Flight Tests.
a. Flight-testing in simulated icing conditions has successfully verified analyses required for approval of IPSs. You may use icing tankers or spray rigs installed on the test aircraft to spray supercooled water drops to simulate icing conditions. Use these simulated icing flight tests to verify drop impingement limits and to determine or verify simulated ice shapes. You may also use the testing to measure heat transfer coefficients, and to show ice shedding from selected aircraft components. Because of the limited size of the icing spray plume, testing is typically limited to small surface areas and components: for example, heated air-data probes, antennas, air inlets (including engine induction air inlets), windshields, and local areas on the wing and empennage.
b. You must measure simulated icing conditions as required by 14 CFR §§ 23.1419,
25.1419, 27.1419, and 29.1419. (See appendix N of this AC for information on instrumentation to measure icing conditions.) Your measurements should characterize icing condition parameters that are useful for understanding the test objectives. Calibrate simulated icing plumes before testing, including the plume’s LWC and uniformity and the spectra of the water drop diameters. Alternatively, provide information that shows current calibration of the icing plume relative to parameters used to produce the plume (spray array water and air pressures, mass flow of the water, water temperature, etc.).
c. Producing the LWC defined in 14 CFR part 25, Appendix C and 14 CFR part 29, Appendix C for small and large drop diameters may be difficult with some spray nozzles.
Therefore, the water catch and resulting ice shapes may differ from that resulting from the icing conditions described in 14 CFR part 25, Appendix C and 14 CFR part 29, Appendix C. Test results from simulated icing flight tests with icing conditions other than those defined in 14 CFR part 25, Appendix C and 14 CFR part 29, Appendix C, should be conservative when compared 24
with results that are in 14 CFR part 25, Appendix C and 14 CFR part 29, Appendix C.
Conservatism should be based on the most adverse results expected from an investigation; larger ice buildups may not lead to conservative test results.
d. See appendix T of this AC for information on simulated icing flight-testing.
8.2.4 Compliance Means: Wind Tunnel Tests.
a. The applicant may use laboratory dry air or simulated icing tests of the components or component models, as necessary, with flight tests in natural icing conditions to verify the ice protection system analyses required by 14 CFR §§ 23.1419(b)(3), 25.1419(b)(3), 27.1419(b)(3), and 29.1419(b)(3). You may also use these compliance means to check for icing anomalies, and to show the effectiveness of the IPS. Appendices R and U of this AC provide guidance on the use of icing wind tunnels. See appendix R, section R.4.2, of this AC for guidance on the use of dry air wind tunnels for determining the aerodynamic effects of ice shapes.
b. You should design icing wind tunnel tests, test conditions, and models to ensure that scaling parameters, such as Reynolds number and Weber number, are similar to those for fullscale flight conditions. If scaling parameters are not similar, you should clearly show how you extrapolated the small-scale test results to full-scale. The extrapolation procedure must be validated. Install the model in the icing wind tunnel to simulate the flight attitude and airplane configuration associated with the most critical flight condition. If you use flaps or other devices on the model to produce the proper flow field conditions, show an agreement between test and full-scale flow conditions.
c. You should address tunnel effects, such as those from the tunnel walls, model blockage, and model support effects, in your analysis.
d. Fluid ice protection systems tested in an icing tunnel should prevent ice formation on the protection surfaces for the designed period of protection. Also, the flow rate of freezing-point depressant fluids should be within the design value.
8.3 Compliance Means: Surfaces Without Ice Protection. Ice buildup may be tolerated on some unprotected aircraft surfaces. The aircraft must have acceptable flying qualities and enough power or thrust to offset the added ice-related drag forces. Ice buildup on control surfaces may be more critical than other airframe surfaces. Provide an analysis and reason for leaving these surfaces unprotected from ice buildup. This analysis must show the aircraft will operate safely in icing conditions without ice protection for these surfaces. If there is doubt about the lack of protection and the adequacy of the provided IPS, you should verify the acceptability of the IPS by flight tests.
8.4 Compliance Means: Ice Inspection Lights and Cues.
a. Unless your aircraft is restricted from flight into known or forecast icing conditions at night, 14 CFR §§ 23.1419(d) and 25.1403 require means for identifying hazardous ice buildups on critical airplane surfaces. You should provide satisfactory lighting for ice inspection during night operation unless you provide another acceptable means of ice inspection (such as a primary 25
flight ice detector system (PFIDS)). (See Reference 2 of section 14 for wing inspection light design criteria.) Evaluate ice inspection lights in and out of clouds during flight in darkness to determine that the target area is illuminated without excessive glare, reflections, or other distractions to the flight crew. You may perform these tests during other airplane certification flight tests. You may use airplane-mounted illumination to comply with these requirements.
The FAA does not consider use of a handheld flashlight acceptable because of the associated additional flight crew workload. The AFM should describe the expected airframe icing cues and the flight crew action associated with the cues.
b. You should provide the flight crew with a means to determine when to activate the ice protection system. Ice buildup on a reference surface, observable by the flight crew, may be an acceptable means, providing you can confirm the airplane will operate safely with ice buildup on the airplane. You should show acceptable ice inspection cues during natural icing flight tests for the applicable aircraft operation, configurations, and phases of flight. The AFM should identify the icing cues and provide the flight crew action associated with the cues.
c. For some airplanes, the critical control surface for ice accretion may not be the wing, but a control surface on the empennage, which is not observable by the flight crew. If the flight crew cannot see the wings or critical empennage control surface, one acceptable means of compliance with 14 CFR §23.1419(d) and §25.1403 is to install an ice evidence probe in a location visible to the flight crew. You should show that formation of ice on this device precedes or occurs simultaneously with ice accretion on the critical surface. You should consider illuminating this device. Another means of compliance is the use of primary inflight icing detectors, where the ice detector sensor becomes the reference surface. See appendix K of this AC for guidance on using ice detectors.
8.5 Compliance Means: Reference to Previously Accomplished Tests.
a. Approval of an IPS by similarity is allowed if other aircraft have been certificated with an IPS that includes components that are functionally and aerodynamically equivalent. (See 14 CFR § 23.1419(c) and AC 23-1419-2C.)
b. If you are seeking approval of ice protection equipment and systems based on previously approved IPSs, you must specify the aircraft model and the component to which the referenced approval applies. Similarity certification may also apply to replacing an IPS component by supplemental type certificate. You must have all the regulatory compliance information from the referenced certification. You should show specific similarities in the physical, functional, thermodynamic, pneumatic, aerodynamic, and environmental exposure. You should perform analyses to show that the component’s installation, operation, ice-protection effectiveness, and the resulting effects on the aircraft’s performance and handling are equivalent to those of the previously approved configuration. You should validate the analysis by test. The analysis may include comparative results from icing and aerodynamic wind tunnel tests, flight tests, engineering simulator laboratory tests, service history, materials laboratory tests, and engineering judgment. However, you should carefully review these analyses to ensure that flight safety remains acceptable and the ice-protection effectiveness, integrity, and operating procedures are acceptable.
c. If the similarity certification is brought about by a change to the airplane type design, you should consider whether the changes in the IPS and associated aircraft behavior are sufficient to require flight-crew training or affect the aircraft’s airworthiness or operational approvals. An assessment of a new installation should consider changes affecting the aircraft and the operation of other aircraft systems. If there is doubt about the effects of the changes, conduct additional tests and analyses to resolve any issues. If there is doubt about resolution of the effects of the differences, conduct flight tests in measured natural icing conditions.
8.6 Compliance Means: Perform Intended Function in Icing Conditions. All aircraft systems and components should function as intended when the aircraft encounters icing conditions.
8.6.1 Compliance Means: Engines and Equipment Performance of Intended Function in Icing Conditions. During icing tests, you must monitor engines and their accessories, such as generators and alternators operating under maximum ice protection load, to ensure that they remain within their limits. (See 14 CFR §§ 23.1041, 25.1041, 27.1041, and 29.1041.)
8.6.2 Compliance Means: Engine Alternate Induction Air Sources Performance of Intended Functions in Icing Conditions. Engine alternate induction air sources should remain functional to ensure satisfactory operation of essential engine subsystems.
8.6.3 Compliance Means: Fuel System Venting Performance of Intended Function in Icing Conditions. Ice accumulation should not adversely affect fuel venting system.
8.6.4 Compliance Means: Landing Gear Performance of Intended Function in Icing Conditions. A retractable landing gear should operate as intended following exposure to icing conditions. Retraction or extension of the landing gear should not cause an unsafe condition or pilot alert because of ice accretion.
8.6.5 Compliance Means: Stall Warning and Protection Performance of Intended Function in Icing Conditions. Ice can form on unprotected stall warning and AOA sensors.
Therefore, the airframe type certificate applicant should evaluate the performance of these sensors during flight in icing conditions. You should ensure acceptable stall warning (aerodynamic or artificial) for ice accumulations on the aircraft. Also, you should provide the same type of stall warning in icing conditions as you provide in non-icing conditions, except the type of stall warning may differ during the brief period between the initial ice buildup and the time that the ice protection system becomes fully effective. You should ensure acceptable stall warning with ice buildups on aircraft surfaces, including the ice buildup occurring before the first activation of the IPS, the ice buildup occurring between the ice protection activation cycles (intercycle ice), the ice buildup remaining after one cycle of the IPS (before landing), and ice buildups on unprotected surfaces. You may need to change the schedules for activating the artificial stall warning, stall identification, and stall protection, if installed, for operations in icing conditions to provide acceptable stall warning margins and to prevent a stall during flight in icing conditions.
8.6.6 Compliance Means: Icing Conditions. You should ensure that ice detection cues used by the pilot to activate the IPS are acceptable at expected aircraft flight attitudes.
8.6.7 Compliance Means: Primary and Secondary Flight Control Surfaces Performance of Intended Function in Icing Conditions. Primary and secondary flight control surfaces should operate normally during and after flight into icing conditions. The airframe type certificate applicant should ensure that aerodynamic- and weight-balanced control surfaces are not subject to icing throughout the aircraft’s operating envelope (weight, center of gravity, and speed). Ensure that any ice buildup on these surfaces does not interfere with the surface actuation, including the operation of high-lift devices, such as slats and trailing edge flaps for safe landing go-around maneuvers.
8.6.8 Compliance Means: Ram Air Turbine Performance of Intended Function in Icing Conditions. The ram air turbine should remain operational during flight in icing conditions.
You may not need to perform natural icing tests if the ram air turbine tested satisfactorily in an icing wind tunnel.
8.6.9 Compliance Means: Pilot Compartment View Performance of Intended Function in Icing Conditions. Note any obstruction of the pilot’s view because of ice buildup to support compliance with 14 CFR §§ 23.773, 25.773(b)(1)(ii), 27.773, and 29.773(b)(1)(ii).
9. AIRPLANE FLIGHT MANUAL (AFM). The AFM must provide the pilot with the information needed to operate the IPS. (See 14 CFR §§ 23.1525 and 23.1583(h), 25.1525 and
25.1583(e), 27.1525 and 27.1583(e), and 29.1525 and 29.1583(e), and 14 CFR §§ 23.1559(c),
27.1559, and 29.1559.)
9.1 AFM: Limitations.
a. You must state in the limitations section of the AFM the atmospheric environments in which the aircraft is approved to operate, including flight into icing conditions. (See 14 CFR §§ 23.1583(h), 25.1583(e), 27.1583(e), and 29.1583(e).)
b. The limitations section of the AFM should include, as applicable, a statement similar to the following: “In icing conditions, the airplane must be operated and its ice protection systems used as described in the operating procedures section of this manual. Where specific operational speeds and performance information have been established for such conditions, this information must be used.” Include in the limitations section of the AFM the following, as appropriate. (See 14 CFR §§ 23.1583(e), 25.1583(a), 27.1581(a)(2), and 29.1581(a)(2).)
(1) The minimum operating airspeed for each normal aircraft configuration whenever ice exists on the critical surfaces.
(2) Instructions to activate the engine anti-ice system when the aircraft encounters Instrument Meteorological Conditions (IMC) at an altitude near or above the freezing level.
(3) Landing weight limits that include the effects on aircraft performance when the IPS is activated. You should consider the effects of residual ice on the aircraft lift and drag, thrust loss associated with operation of the IPS, and the airplane performance at the recommended operating speeds. You may present these weight limits in the performance information section of the AFM and include them as aircraft limits by specific reference in the AFM’s FAA-approved limitations section.
(4) Limits on operating time for ice protection equipment, if these limitations are based on fluid anti-ice/deice systems capacities and flow rates.
(5) Airspeed limits (if any) and the minimum temperature at which the deicing boots may be operated.
(6) Environmental limits for operating deicer boots, such as minimum temperature and maximum altitude for boot operation.
(7) Minimum engine rpm or power setting necessary for the airframe IPS to function properly.
(8) A list of required placards.
(9) Severe icing warnings. (See AC 23.1419-2C and AC 25.1419-1A.)
9.2 AFM: Operating Procedures.
a. The AFM operating procedures for flight in icing conditions should include instructions for normal operation of the airplane, including operation of the aircraft when the IPS fails. In the AFM, you must also include procedures for managing other airplane system failures that will affect the IPS of the airplane in icing conditions.
(1) You must provide the pilot with recommended procedures that are unique to your aircraft for safe flight. (See 14 CFR §§ 23.1585(a), 25.1585(a), 27.1585(b), and 29.1585(a).)
These procedures should include any necessary preflight action that minimizes the potential for enroute emergencies associated with the IPS. You should describe the system components with enough clarity and depth so the pilot can understand the component’s function. Unless flight crew actions are accepted as normal airmanship, such as maintaining situational awareness, you should include the appropriate procedures in the FAA-approved AFM or AFM supplement.
These procedures should include proper pilot response to cockpit warnings, a way to diagnose system failures, and how to use system(s) safely.
b. Normal operating procedures.
(1) Normal operating procedures in the AFM should reflect the procedures used to certificate the airplane for flight in icing. This includes configurations, speeds, ice protection system operation, and power plant and systems operation. You should provide this information for all phases of flight, including takeoff, climb, cruise, descent, holding, go-around, and landing.
(2) You should provide procedures to optimize aircraft operation during flight in icing conditions. You should provide these procedures for flight phases in which icing conditions are commonly encountered, including climb, holding, and approach, and ETOPS diversions. The AFM should define when the flight crew must activate the ice protection equipment.
(3) For fluid IPSs, provide information and method(s) for determining the remaining flight operation time.
c. Abnormal and emergency procedures.
(1) The AFM must contain an emergency or abnormal operating procedures section describing flight crew actions if annunciated IPS failures and suspected unannunciated failures occur. Also, include any changes to other AFM abnormal procedures resulting from flight in icing conditions.
(2) For aircraft that cannot supply enough electrical power for all systems with an electrical system failure or engine failure, give the pilot load-shedding instructions.
9.3 AFM: Performance Information. You must provide performance information in the AFM for all flight phases affected by flight into icing conditions (14 CFR parts 23 Subpart B, 25 Subpart B, 27 Subpart B, and 29 Subpart B). Provide information to allow the flight crew to determine climb-limited aircraft weight, altitude, and temperature (WAT) limits in icing conditions. These data should include the effects of drag resulting from ice buildups (including ice buildups on unprotected surfaces and intercycle ice on protected surfaces), the power extraction associated with IPS operation, and any changes in operating speeds due to icing.
Show the effect on landing distance due to the increased landing speeds and for all landing configurations when landing in icing conditions.
9.4 AFM: Airworthiness Directives for Severe Icing Conditions.
a. In October 1994, an accident occurred involving a transport category airplane operating in severe icing conditions. The accident airplane ’s loss of control profile was replicated by ice shapes developed during extensive flight testing in simulated large-drop icing conditions. The simulated cloud water drop diameters were consistent with freezing drizzle. This condition created a ridge of ice aft of the wing’s upper surface deicing boots and forward of the ailerons, resulting in an uncommanded motion of the ailerons, control force anomalies, and the rapid roll of the aircraft.
b. Following this accident, the FAA determined flight crews are not provided the information necessary to determine when they are likely to experience icing conditions for which the airplane is not certificated. As a result of these findings, the FAA determined that flight crews must be provided the information on current weather conditions, and be made aware of specific visual cues that may indicate when their airplane is operating in atmospheric conditions outside the 14 CFR part 25, Appendix C icing envelopes.
c. The FAA issued a series of airworthiness directives (AD) for airplanes equipped with pneumatic deicing boots and non-powered roll control systems in April 1996 and February 1998.
The ADs required revising the AFM to provide the flight crew with recognition cues and procedures for exiting from severe icing conditions, and to limit or prohibit the use of trailing edge flaps and the autopilot.
d. The limitations and procedures in AD 96-09-25 contain acceptable ways to provide this information. These limitations and procedures should be applied to all airplanes with reversible lateral controls approved for flight in icing, and should include, but are not limited to, the following:
(1) Visual cues that the airplane is in severe icing conditions;
(2) Prohibition on the use of the autopilot when the visual cues are observed;
(3) All icing inspection lights operative before flight into icing conditions at night;
(4) Immediate exiting of the severe icing conditions; and
(5) If the flaps are extended, do not retract them until the airframe is clear of ice.
NOTE: Retracting the flaps is contingent on the existence of a means to determine if the airplane surfaces are clear of ice.
10. ROTORCRAFT.
10.1 Rotorcraft: General.
a. This section contains additional guidance on certificating rotorcraft IPSs. This guidance is necessary because certification considerations for rotorcraft IPSs and fixed-wing airplanes differ due to design and operation differences. Rotor blades operate in a much wider range of airspeeds than that of a fixed-wing of an airplane, resulting in different ice accretion characteristics. Attention to the structural integrity of the main rotor blades and tail rotor blades, rotorcraft vibration, shed-ice hazards, and instrument performance is crucial for rotorcraft.
AC 29-2C, Section 29.1419, can guide you on compliance with 14 CFR § 29.1419, and AC 27-1B can guide you on rotorcraft certificated to the requirements of 14 CFR part 27.
b. The objective of rotorcraft icing certification is to show the rotorcraft will operate safely throughout its approved icing envelope. This objective includes determining the rotorcraft’s limits when operating in icing conditions, for example, showing that the icing warning means and the IPS are acceptable. A limitation may result, for example, from considerations of aircraft handling qualities, performance, autorotation, asymmetric ice shedding from the rotors, or visibility through the windshield.
c. For rotorcraft operations, icing conditions defined in 14 CFR part 29, Appendix C may be truncated to a pressure altitude of 10,000 feet or the altitude limit of the aircraft if lower than 10,000 feet. Air traffic compatibility constraints discourage approval of a maximum altitude less than 10,000 feet. However, there are operations where a lower maximum altitude has no effect on the air traffic system and would still be operationally useful. If you elect to certificate your 31
rotorcraft with a 10,000 pressure altitude limit based on an equivalent level of safety, you may select icing condition envelopes contained in AC 29-2C. (For pressure altitude above 10,000 feet, AC 29-2C states that 14 CFR part 29, Appendix C icing conditions must be used.)
d. The icing conditions contained in AC 29-2C were derived from an analysis, performed by the FAA William J. Hughes Technical Center during 1985, of the data used to establish the icing conditions contained in 14 CFR part 29, Appendix C. There are significant differences between the two icing environments. For example, the AC 29-2C icing envelopes for altitudes of 10,000 feet and lower specifies temperatures colder than -10 °F and 0 °F need not be addressed for continuous and intermittent icing conditions, respectively. Comparative temperatures in 14 CFR part 29, Appendix C specify -22 °F and -6 °F. Also, the minimum altitude specified in AC 29-2C identifies intermittent icing conditions occurring at 4,000 feet, whereas 14 CFR part 29, Appendix C specifies a value starting at sea level. Since icing conditions identified in AC 29-2C are not regulatory and are less rigorous than those required by 14 CFR part 29, Appendix C (14 CFR §§ 27.1419 and 29.1419), you should consult the FAA before using the AC 29-2C icing conditions for compliance with 14 CFR parts 27 and 29 icing requirements.
e. Use the required icing conditions for determining the most critical combinations of icing and rotorcraft operating conditions as a function of enroute distance. This, combined with a 30-minute destination-hold in icing conditions, is in lieu of the fixed-wing aircraft destinationhold policy. The rotorcraft 30-minute destination-hold assessment, a means of compliance with 14 CFR § 29.1419, should consider the LWC at the standard cloud extents of 17.4 nm and
2.6 nm for continuous maximum and intermittent maximum icing conditions, respectively. (See AC 29-2C.) Carefully evaluate all the required icing condition envelopes during certification of the IPS.
f. The effects of ice accumulation on rotorcraft will vary among makes and models of rotorcraft. Experience gained from certificating a rotorcraft system could provide valuable information but should be used cautiously when using an identical blade profile on a new rotorcraft for which approval for flight in icing is requested. Exercise particular care when drawing from experience gained from fixed-wing icing encounters because the icing conditions effects on rotor blades may be incompatible with fixed-wing results.
g. Although military rotorcraft icing technology and operational experience provide useful background information, you must show compliance with 14 CFR parts 27 and 29 in-flight icing requirements. Information on rotor blade ice protection and rotorcraft ice protection system design is in Reference 3 of section 14.
10.2 Rotorcraft: Compliance.
a. Compliance with the certification requirements for flight into icing conditions is established when:
(1) The engine(s) will not flameout or experience significant power losses or damage because of ingestion of ice shedding from airframe surfaces or clogging of air intake screens;