the potential of enroute emergencies associated with the ice protection system. The system components should be described with sufficient clarity and depth that the pilot can understand their function. Unless flight crew actions are accepted as normal airmanship, the appropriate procedures should be included in the FAA-approved AFM, AFM revision, or AFM supplement.
These procedures should include proper pilot response to cockpit warnings, a means to diagnose system failures, and the use of the system(s) in a safe manner.
(b) Procedures should be provided to optimize operation of the airplane during penetration of icing conditions, including all flight regimes. The AFM should include procedures that advise upon which conditions the ice protection equipment should be activated.
(c) Emergency or abnormal procedures, including procedures to be followed when ice protection systems fail and/or warning or monitor alerts occur, should be provided.
(d) For fluid anti-ice/deice systems, information and method(s) for determining the remaining flight operation time should be provided.
(e) For airplanes that cannot supply adequate power for all systems at low engine speeds, load-shedding instructions should be provided to the pilot for approach and landing in icing conditions.
(f) For aircraft equipped with an autopilot, the autopilot should be disconnected periodically to check for unusual control force or deflection, and to move the flight controls to check for evidence of ice accreting in control surface gaps or frozen actuators.
(3) Performance Information Section. A brief statement that supercooled cloud test environment and freezing rain, freezing drizzle, or mixed conditions (as appropriate) have not been tested. These icing environmental conditions outside the icing envelope of part 25, Appendix C, may exceed the capabilities of the ice protection system, and it may result in a serious degradation of performance or handling characteristics.
(a) Normal, Utility, and Acrobatic Category Airplanes. For these airplanes, general performance information should be provided to give the pilot knowledge of allowances necessary while operating in ice or with residual ice on the airframe. The following items are only examples that provide some guidelines and are not requirements. These guidelines may be revised for specific airplanes as appropriate:
1. An accumulation of inch of ice on the leading edges can cause a loss in rate of climb up to Feet Per Minute (FPM), a cruise speed reduction of up to KIAS, as well as a significant buffet and stall speed increase (up to knots). Even after cycling the deicing boots, the ice accumulation remaining on the boots and unprotected areas of the airplane can cause large performance losses. With residual ice from the initial inch accumulation, losses up to FPM in climb, KIAS in cruise, and a stall speed increase of knots can result. With inch of residual accumulation, these losses can double.
2. Airspeed—MAINTAIN BETWEEN KIAS AND KIAS with ____ inch or more of ice accumulation for appropriate configuration.
3. Prior to a landing approach cycle the wing and stabilizer deice boots to shed any accumulated ice. Maintain extra airspeed on approach to compensate for the increased stall speed associated with ice on unprotected areas. Use caution when cycling the boots during an approach, since boot inflation with no ice accumulation may cause mild pitching and increase stall speeds by knots. It may also decrease stall warning margin by the same amount; and it may cause or increase rolling tendency during stall.
4. Holding in icing conditions for longer than 45 minutes may reduce margins and could result in inadequate handling and control characteristics.
5. Maintain engine speeds of RPM higher to assure proper operation of the ice protection system.
(b) Commuter Category Airplanes. Data should be provided so that the balked landing climb limited weight and approach climb limited landing weight could be determined.
These data should include the effect of drag due to residual ice on protected and unprotected surfaces, power extraction associated with ice protection system operation, and any changes in operating speeds due to icing. Also, the effect on landing distance due to revised approach speeds, and/or landing configurations, should be shown.
(4) For airplanes with a certification basis at amendment 23-14 or higher, the AFM should contain a statement similar to “This airplane is approved for flight in icing conditions as defined in part 25, Appendix C.” For these airplanes, there should not be references to operational terms such as “light” or “moderate” ice or “known icing.”
(5) The AFM should reference the maintenance manual for ice protection surface cleaning procedures if the flight crew can be expected to perform this function.
c. Prior to AFM Requirement. If the airplane was certificated prior to the effective date of the requirement for an AFM, then the combination of manuals, markings, and placards should adequately address the placard and AFM subjects previously discussed in this AC.
15. INSTRUCTIONS FOR CONTINUED AIRWORTHINESS.
a. Pneumatic Deicing Boots. Boot manufacturers have developed repair procedures for pinholes, cuts and tears. The repair process for these types of damage is critical because proper operation of the boots could be affected. If leaks or pinholes are not periodically repaired, the entire system could become inoperable if water, drawn in by the vacuum that holds the boots deflated, subsequently refreezes and blocks a pneumatic line. The performance of deicing boots is dependent on the height and speed of deicing boot inflation and of the composition of the surface ply and its ice adhesion characteristics. Repairs should not pinch off tubes and thereby 48
reduce inflation height. With these concerns in mind, the following guidance represents a minimum that should be addressed for repair procedures:
(1) Testing. The following tests should be accomplished:
(a) Boot Cycle Testing. The integrity of the repair should be evaluated via boot cycling at the maximum normal system operating pressure. Cycling should continue until the repair or boot fails. The normal deflation time may be shortened to speed up the test. For example, a 174-second deflation cycle can be reduced to 18 seconds while maintaining the six-second inflation time. Any material applied to the whole surface of the boot should also be evaluated in this test.
(b) Cold Temperature Cycling. The testing in (1)(a) should be repeated at a temperature of zero degrees F or colder.
(c) Hot Temperature. The boots may be exposed to hot temperatures, especially after on the ground on a hot, sunny day. The combination of high temperature and fluid exposure may cause deterioration and should be evaluated, see paragraph (e).
(d) Proof and Burst Pressure Testing. This testing should be accomplished to show compliance to § 23.1438(b). When conducting the proof pressure test at 1.5 times maximum operating pressure, the repaired deicing boot should hold that pressure for 60 seconds and the repair should not fail. After the proof pressure test, the system should be inflated at maximum operating pressure, isolated, and the pressure drop verified not to exceed three Pounds Per Square Inch (PSI) in one minute.
(e) Fluids Susceptibility. The repair should be exposed to various fluids for at least 24 hours in combination with a high temperature (160 degrees F) and the boots cycled at nominal pressure for at least 24 hours. Fluids to be evaluated include: fuels, oil, hydraulic fluids, glycol/water mixture, deicing boot age reduction, surface treatments and ice adhesion products, and ground deicing fluids. One method of accomplishing this test is to soak a rag with the fluid, place on the deicing boot over the repair, seal to prevent evaporation, and place in an oven at 160 degrees F for 24 hours. Following this exposure the boot is removed, and cycled for 24 hours. The deicing boot should inflate and hold air, and the repairs should remain in place and not leak air.
(f) Sand and Rain Erosion. Sand and rain erosion testing should be accomplished to show that the repair does not erode at a greater rate than the boot. A typical sand erosion test is ASTM G-76-95. A typical rain erosion test is conducted on a whirling arm rig that exposes the boot to a rainfall rate of one inch per hour at 300 to 500 Mile Per Hour (MPH) (depending on the airplane maximum speed), using one to two Millimeter (mm) diameter drops.
(g) The inflation height over the repaired area should be measured and compared against other unrepaired portions of the boot at temperatures covering the part 25, Appendix C envelope.
(h) Ice Shedding. Ice shedding performance in the area of the repair, and of the whole boot if any material is applied to the whole boot, should be evaluated throughout the part 25, Appendix C continuous maximum and intermittent maximum icing conditions. It is particularly important to cover the range of temperatures and liquid water contents of part 25, Appendix C and the expected operational airspeeds. Simulated icing tests, such as an icing tunnel, may be used.
(2) Materials Properties. Any material applied to the boots should be compatible with the deicing boot material. Use of brittle repair materials is not recommended. If the boot is completely resurfaced with a material, that material should be electrically conductive to allow bleeding of static charge from the deicing boot.
(3) Repair Process Limitations. The repair process should contain limitations and quality control procedures such as:
(a) Size of repairs. The maximum allowed repair size should be established and tested. Another consideration is the effect of the repair failure on the airplane.
(b) Location and depth of repairs. Can structural elements such as tube fabric or stitches be damaged or can the wrong internal layers, such as tube fabric, be bonded together?
It is recommended that boot manufacturers limits be used.
(c) Density of repairs. The maximum density of repairs (number per area) should be tested. It is recommended that boot manufacturers limits be used.
(d) Application of solvents and other chemicals. The application of solvents and other chemicals used in the repair process that can disbond the boot should be controlled so that they cannot penetrate internal layers of the boot.
(e) Applicability of the repair procedure. Broken stitches represent a structural failure of the boot and should not be repaired. There should also be guidelines as to when severely worn boots should be replaced.
b. Electrothermal Propeller and Engine Inlet Deicing Boots. Boot manufacturers historically have not developed repair procedures for electrothermal deicing boots because the thermal mass characteristics of the repaired location will change and affect ice shedding. The following guidance is a minimum that should be addressed for electrothermal boot repairs:
(1) Testing. The following tests should be accomplished:
(a) Fluids Susceptibility. The repair should be exposed to various fluids and the boots operated. Fluids to be evaluated include: fuels, oil, hydraulic fluids, glycol/water mixture, deicing boot age, appearance and ice adhesion products, and ground deicing fluids.
(b) Sand and Rain Erosion. Sand and rain erosion testing should be accomplished to show that the repair does not erode at a greater rate than the boot.
(c) Thermal Characteristics. The thermal conductivity of the repair should be evaluated to insure that it does not provide a “cold spot” on the deicing boot, resulting from either a higher thermal mass or lower thermal conductivity of the repair material.
(d) Ice Shedding. Ice shedding performance in the area of the repair, and of the whole boot if any material is applied to the whole boot, should be evaluated throughout the part 25, Appendix C, continuous maximum and intermittent maximum icing conditions.
Simulated icing tests, such as an icing tanker, may be used.
(e) Vibration. The airplane should be tested in icing conditions to verify the repair on one blade does not directly or indirectly (due to ice shedding) cause unacceptable propeller vibration.
(2) Materials Properties. Any material applied to the boots should be compatible with the deicing boot material. Use of brittle repair materials is not recommended. The material should be electrically non-conductive and should have similar thermal conductivity of the deicing boot material. The effect of the chemicals on the electrical wires or foil should be evaluated.
(3) Repair Process Limitations. The repair process should contain limitations and quality control procedures such as:
(a) Size of repairs. The maximum allowed repair size should be established and tested. Another consideration is the effect of the repair failure on the airplane.
(b) Location and depth of repairs. Can heating elements such as wires or etched foil be damaged or can the resistance of the wire or foil be altered by the repair procedure?
(c) Density of repairs. The maximum density of repairs (number per area) should be tested.
(d) Application of chemicals. Can the application of too much chemicals penetrate the boot and cause internal debonding of the boot?
(e) Applicability of the repair procedure. Can the repair be accomplished on severely worn boots?
51 and 52
Appendix A
APPENDIX A. DEFINITIONS
1. DEFINITION OF TERMS. For the purposes of this AC, the following definitions should be used.
a. Anti-Ice. The prevention of ice formation or accumulation on a protection surface, either by evaporating the impinging water or by allowing it to run back and off the surface or freeze on non-critical areas.
b Part 25, Appendix C Icing Conditions. Part 25 Appendix C certification icing condition standard for approving ice protection provisions on aircraft. The conditions are specified in terms of altitude, temperature, LWC, representative droplet size (MED), and cloud horizontal extent.
NOTE 6 In part 25, Appendix C, the term “mean effective diameter” refers to what is now called the “Median Volume Diameter (MVD),” determined using rotating multi-cylinders and assuming a Langmuir distribution.
c. Artificia l Ice. Real ice, but formed by artificial means, such as a spray rig in a tunnel or on a tanker.
d. Critica l Ice. The aircraft surface ice shape formed within required icing conditions that results in the most adverse effects for specific flight safety requirements. For an aircraft surface, the critical ice shape may differ for different flight safety requirements, e.g., stall speed, climb, aircraft controllability, control surface movement, control forces, air data system performance, dynamic pressure probes for control force “feel” adjustment, ingestion and structural damage from shed ice, engine thrust, engine control, and aeroelastic stability.
e. Deice or Deicing. The periodic shedding or removal of ice accumulations from a surface, by destroying the bond between the ice and the protection surface.
f. Freez ing Drizzle. Drizzle is precipitation on the ground or aloft in the form of liquid water drops that have diameters less than 0.5 mm and greater than 0.05 mm (100 µm to 500 µm).
Freezing drizzle is drizzle that exists at air temperatures less than 0 degrees C (supercooled), remains in liquid form, and freezes upon contact with objects on the surface or airborne.
g. Freez ing Precipitation. Any form of liquid precipitation that freezes upon impact with the ground or exposed objects, that is, freezing rain or freezing drizzle.
h. Freez ing Rain. Rain is precipitation on the ground or aloft in the form of liquid water drops which have diameters greater than 0.5 mm. Freezing rain is rain that exists at air temperatures less than zero degrees C (supercooled), remains in liquid form, and freezes upon contact with objects on the surface or airborne.
A-1
Appendix A
i. Ice Crystals. Any one of a number of macroscopic, crystalline forms in which ice appears.
j. Icing Conditions. The presence of atmospheric moisture and temperature conducive to airplane icing.
k. Intercycle Ice. Ice that accumulates on a deiced surface that exists just prior to the actuation of the deice system.
l. LWC. The total mass of water contained in liquid drops within a unit volume or mass of air, usually given in units of grams of water per cubic meter (g/m3) or kilogram of dry air (g/kg).
m. MED. The calculated drop diameter that divides the total liquid water content present in the drop size distribution in half, i.e., half the water volume will be in larger drops and half the volume in smaller drops. The value is calculated, based on an assumed droplet size distribution,
(e.g. Langmuir distribution) which is how it differs from median volume diameter.
n. MVD. The drop diameter that divides the total liquid water content present in the drop distribution in half, i.e., half the water volume will be in larger drops and half the volume in smaller drops. The value is obtained by actual drop size measurements.
o. Mixed Phase Icing Conditions. A homogeneous mixture of supercooled water drops and ice crystals existing within the same cloud environment.
p. Monitored Surface. The surface of concern regarding the ice hazard, (e.g., the leading edge of a wing). Ice accretion on the monitored surface may be measured directly or correlated to ice accretion on a reference surface.
q. Pre-Activation Ice. Protected surface ice accretion prior to the full effectiveness of the ice protection system.
r. Protected Surface. A surface containing ice protection, typically located at the surface’s leading edge.
s. Protection Surface. Active surface of an ice protection system, for example, the surface of a deicing boot or thermal ice protection system.
t. Reference Surface. The observed (directly or indirectly) surface used as a reference for the presence of ice on the monitored surface. The presence of ice on the reference surface must occur prior to – or coincidentally with – the presence of ice on the monitored surface. Examples of reference surfaces include windshield wiper blades or bolts, windshield posts, ice evidence probes, propeller spinner ice, and the surface of ice detectors. The reference surface may also be the monitored surface.
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Appendix A
u. Residual Ice. Ice that remains on a protected surface immediately following the actuation of a deicing system.
v. Reversible Flight Controls. The flight deck controls are connected to the pitch, roll, or yaw control surfaces by direct mechanical linkages, cables, or push-pull rods such that pilot effort produces motion or force about the hinge line. Conversely, force or motion originating at the control surface (through aerodynamic loads, static imbalance, or trim tab inputs, for example) is transmitted back to flight deck controls.
(1) Aerodynamically Boosted Flight Controls: Reversible flight control systems that employ a movable tab on the trailing edge of the main control surface linked to the pilot's controls or to the structure in such a way as to produce aerodynamic forces that move, or help to move, the surface. Among the various forms are flying tabs, geared or servo tabs, and spring tabs.
(2) Pow er-Assisted Flight Controls: Reversible flight control systems in which some means is provided, usually a hydraulic actuator, to apply force to a control surface in addition to that supplied by the pilot to enable large surface deflections to be obtained at high speeds.
w. Runback Ice. Ice formed from the freezing or refreezing of water leaving an area on an aircraft surface that is above freezing and flowing downwind to an area that is sufficiently cooled for freezing to take place. This ice type is frequently a byproduct of partially evaporative (running wet) ice protection systems.
x. Simulated Ice. Ice shapes that are fabricated from wood, epoxy, or other materials by any construction technique.
y. Supercooled Large Drops (SLD). Supercooled liquid water that includes freezing rain or freezing drizzle.
z. Supercooled Water. Liquid water at a temperature below the freezing point of zero degrees C.
2. DEFINITION OF ACRONYMS.
AC Advisory Circular ACO Aircraft Certification Office AFM Airplane Flight Manual AIR Aerospace Information Report APU Auxiliary Power Unit ARP Aerospace Recommended Practice AS Aerospace Standard C Centigrade CAR Civil Air Regulations CFR Code of Federal Regulations A-3
Appendix A
CG Center of Gravity CS Certification Specification (EASA) F Fahrenheit FAA Federal Aviation Administration FPM Feet Per Minute EASA European Aviation Safety Agency EFIS Electronic Flight Information Systems ICTS Ice Contaminated Tailplane Stall IIDS In-Flight Ice Detection System IMC Instrum ent Meteorological Conditions IPS Ice Protection System KCAS Knots Calibrated Airspeed KIAS Knots Indicated Airspeed KOEL Kind of Equipment List LWC Liquid Water Content MDI Magnetic Direction Indicator MED Mean Effective Diameter MFC Maximum Mach number for stability characteristics MMEL Master Minimum Equipment List MOC Means Of Compliance MSL Mean Sea Level MVD Median Volume Diameter NTSB National Transportation Safety Board OAT Outside Air Temperature PIIDS Primary In-Flight Ice Detection System PMA Parts Manufacturing Approval POH Pilot's Operating Handbook PSI Pounds Per Square Inch PSIG Pounds Per Square Inch Gauge RGL Regulatory and Guidance Library RPM Revolutions Per Minute SAE Society of Automotive Engineers SLD Supercooled Large Drops STC Supplemental Type Certificate TC Type Certificate TCDS Type Certificate Data Sheet TSO Technical Standard Order VMC Minimum Control Airspeed VMO Maxim um Operating Airspeed MMO Maxim um Operating Mach Number VNE Never Exceed Airspeed VREF Reference Landing Approach Airspeed
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Appendix B
APPENDIX B. GUIDELINES FOR DETERMINING CERTIFICATION BASIS ON
FLIGHT IN ICING APPROVAL STCS AND AMENDED TCS
1. My CAR 3 aircraft has ice protection systems installed and is not placarded against flight into known icing. Am I approved for flight in icing conditions?
These CAR 3 airplanes are permitted to fly in icing conditions if:
• the ice protection systems are installed per type design data of the same model in the Type Certificate Data Sheet (TCDS);
• the POH, AFM, or AFM supplement associated with the ice protection systems do not prohibit it;
• the equipment listed in the KOEL are installed and functioning; and
• the airplane complies with the equipment requirements of § 91.527 or § 135.227, if applicable.
2. What if I have a CAR 3 airplane that is permitted to fly in icing conditions but I replace the ice protection system with another system?
It depends on what is meant by another system. If it is replacement parts, such as replacing pneumatic deicing boots with those from another manufacturer, the certification basis can remain unchanged; see Appendix E for more information. If it is another type of system, for example replacing a pneumatic deicing system with a freezing point depressant system or electrothermal system, compliance to § 23.1419, amendment 23-14 must be shown. Section 23.1419, amendment 23-43 would not be required since a modification to an ice protection system is considered “not significant” under the Changed Product Rule.
3. As a follow-up to the last question, suppose I change my mind and want to re-install my ice protection systems. Will my aircraft be approved for flight in icing?
Yes, as long as the systems are installed per type design data and the POH, AFM, or AFM supplement associated with the ice protection systems do not prohibit flight in icing conditions (or “flight into known icing”). Retroactive removal of flight into known icing approval can only be accomplished by the airworthiness directive process.
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Appendix B
4. I have a CAR 3 airplane that has no ice protection system installed and the type design data does not contain flight in icing approval. What is the certification basis if I add ice protection systems?
Under the Changed Product Rule, adding approval for flight in icing conditions is considered a significant change (AC 21.101-1) and compliance should be shown to the latest amendment. In addition, § 91.527 or § 135.227, if applicable, has a minimum requirement of equipment. The applicable regulations for an icing certification are:
23.603 23.1093 23.1301 23.1327 23.1501 23.1581
23.773 23.1095 23.1309 23.1351 23.1525 23.1583
23.775 23.1097 23.1323 23.1357 23.1529
23.905 23.1099 23.1325 23.1416 23.1547
23.929 23.1101 23.1326 23.1419 23.1559
It is recognized that compliance to § 23.1419(a), which requires that the airplane meet Subpart B performance in icing conditions, may be impractical for some CAR 3 airplanes. The Changed Product Rule allows the applicant to elect compliance to amendment 23-14 for that particular paragraph of § 23.1419. In this case the performance regulations are used as guidelines as discussed in paragraph 12a(2) of this AC.
5. My airplane has some ice protection systems installed but is not certified for flight in icing. A later model of my airplane, which is on the same TCDS, is certified for flight in icing in accordance with § 23.1419. The later model does have a different engine installed with higher horsepower and a different ice protection system. Can I install the exact same ice protection systems as the later model, install a new engine with at least the same horsepower, and be certified for flight in icing?
Yes, and similarity may be used to show compliance to the applicable regulations. However, there may be some testing required. The current method of compliance to § 23.1419 includes tests (susceptibility to ice contaminated tailplane stall, for example) that may not have been accomplished during certification of the later model.
B-2