Appendix D
c. To show compliance to § 23.1351 an electrical load analysis should be done if the ice protection system utilizes the airplane’s primary electrical power system. If the ice protection system utilizes its own alternator/generator, other regulations in § 23.1351 may be applicable.
d. Compliance to § 23.1416 and § 23.1419 are not required.
6. SUBPART G – OPERATING LIMITATIONS AND INFORMATION.
a. A cockpit placard in view of the pilot and the AFM should state that the airplane is prohibited from flight in icing conditions.
b. A description of all ice protection system controls and annunciations should be in the AFM.
c. If the airplane is equipped with a stall warning sensor(s) that are not heated, the AFM should caution that stall warning in icing conditions might not be reliable.
d. Instructions for continued airworthiness in accordance with § 23.1529 should be provided.
D-3 and D-4
Appendix E
APPENDIX E. GUIDELINES FOR APPROVAL OF REPLACEMENT
PARTS FOR AIRFRAME DEICING SYSTEMS
1. The requirements leading to approval of replacement airframe deicing systems (propellerdeicing systems will be addressed in a revision) or airframe thermal deicing or anti-icing systems are functions of the project certification basis and similarity with the original part(s), as summarized in Table E-1 and discussed in the following paragraphs:
TABLE E-1. SUMMARY OF TEST REQUIREMENTS FOR REPLACEMENT AIRFRAME
DEICING COMPONENTS
Aircraft Approved for Flight in Icing Conditions?
Certification Basis Approval Process Required Tests to Show Safe Operation throughout Part 25, Appendix C Icing Conditions Natural Icing Flight Tests
No PMA Not required Not required
Yes CAR § 3.712 STC See paragraph b. See paragraph b.
Yes 23-0 to 23-13 STC See paragraph b. See paragraph b.
Yes 23-14 to 23-42 STC Required See paragraph c.
Yes 23-43 or higher STC Required Required
a. For aircraft whose certification basis does not include CAR § 3.712 or § 23.1419, the deicing system is optional equipment and not required. In this case, the replacement parts can be approved via the Parts Manufacturing Approval (PMA) process in 14 CFR, part 21, subpart K.
The replacement parts must be shown to function properly, remove ice or prevent ice accretion as well as the previously installed equipment, and not introduce additional failure modes that could prevent continued safe flight and landing. Comparative tests of the original versus the replacement parts are acceptable.
b. For aircraft whose certification basis is CAR § 3.712 or an original issue under § 23.1419, an STC is required. Original certification of these aircraft only required that pneumatic deicers be installed per approved data and that they have a positive means of deflation. No icing flight tests were required, and airplanes were considered “approved for flight into known icing” when the airplane was equipped with a complement of certificated deicing or anti-icing equipment spelled out in operational requirements. For replacement parts in these aircraft it is advisable for the Aircraft Certification Office (ACO) to contact the ACO maintaining the original type design data to determine factors such as variance with the original design, the original certification requirements, and the service history of the original product.
The replacement parts must be shown to function properly, remove ice or prevent ice accretion E-1
Appendix E
as well as the previously installed equipment, and not introduce additional failure modes that could prevent continued safe flight and landing. Comparative tests of the original versus the replacement parts may be acceptable. If the original certification basis is to be utilized, it is highly recommended that an entry in the AFM supplement limitations section, or a placard, with the following wording be required: “This airplane has not demonstrated compliance with the icing environment requirements of 14 CFR, part 25, Appendix C.
c. For replacement parts on an aircraft whose certification basis is § 23.1419, amendments 23-14 through 23-42, an STC is required. Flight testing in measured, natural icing conditions should be accomplished if the replacement parts are of different materials or have different design characteristics. Supplemental testing in artificial icing conditions (icing tunnel, tanker) should also be accomplished to cover the complete part 25, Appendix C envelope. The replacement parts must be shown to function properly, remove ice or prevent ice accretion as well as the previously installed equipment, and not introduce additional failure modes that could prevent continued safe flight and landing. A matrix of performance and flying qualities as discussed in paragraph 12a(2) of this AC should be accomplished. The Standards Office should be contacted since the requirement to flight test in measured, natural icing conditions is dependent on a number factors such as whether AFM performance in icing conditions is based on protected surface ice accretions, the service history of the airplane, and flight testing accomplished during the original certification with protected surface ice accretions. Follow-on applications of the new parts in aircraft other than the initial certification may then be approved through similarity provided the conditions in § 23.1419(c) are met. There may be cases where minor modifications would not require additional measured, natural flight tests.
d. For replacement parts on an aircraft whose certification basis is § 23.1419, amendment 23-43 or higher or those aircraft where the applicant wants to add “flight in icing conditions” operational approval, an STC is required. Flight testing in measured, natural icing conditions is required if the replacement parts are of different materials or have different design characteristics. Supplemental testing in simulated icing conditions (icing tunnel, tanker) may also be required to cover the complete part 25, Appendix C envelope. The replacement parts must be shown to function properly, remove ice or prevent ice accretion as well as the previously installed equipment, and not introduce failure modes that could prevent continued safe flight and landing. A matrix of performance and flying qualities as discussed in paragraph 12a(1) of this AC should be accomplished. Follow-on applications of the new parts in aircraft other than the initial certification may then be approved through similarity provided the conditions in § 23.1419(c) are met. There may be cases where minor modifications would not require additional measured, natural flight tests.
2. Engineering judgment must be used to determine that the modifications would not affect the effectiveness of the ice protection in natural icing conditions. If there is any question as to the need for a particular design to be subject to natural icing tests, the ACO should contact the Standards Office as well as the ACO that performed the original certification and the national resource specialist for aircraft icing. Again, seemingly benign differences can have significant negative effects on an aircraft's ice protection capability.
E-2
Appendix F
APPENDIX F. CHECKLIST
The left column of this appendix provides a simplified checklist of the various influence items that could affect the safety of small airplanes while operating in icing conditions. In the right column are suggested considerations for resolving the concerns of each of these influence items.
Certain considerations may not be applicable depending on the certification basis of the airplane.
See Table F-1.
TABLE F-1. CHECKLIST
Influence Consideration
1. Crew Visibility
a. Conduct evaluations to verify adequate day and night visibility through the protected windshield or the protected windshield segment under dry air and icing conditions.
b. Evaluate the cabin defogging system's capability to clear side windows for observation of boot ice protection system operation and ice accumulation. If a defogging system is not provided, the windows should be easily cleared by the pilot without adversely increasing pilot workload.
c. Minimum light transmittance through the protected windshield or protected windshield segment and effected side windows should consider the requirements in § 23.775(e).
d. Determine that the temperature gradient produced on heated windshields does not adversely affect pilot vision or windshield structural integrity.
2. Engine Installation and Cooling Conduct flight tests, analyses, or refer to substantiation data to determine that complete engine installation, including propellers, functions without appreciable loss of power. Verify that engine oil and component cooling is adequate at critical design points throughout the operational and icing envelope. If data is analyzed in accordance with § 23.1043, the temperatures need to be corrected only to 32 degrees F, not a hot day. If ice is expected to accumulate at the generator during icing encounters, then cooling air inlet generator cooling tests should be performed with the maximum icing load on the electrical system and critical ice shapes installed on the engine and generator cooling air intake.
3. Propeller a. Provide analyses to establish chordwise and spanwise protection required. Aerodynamic heating due to blade rotation, latent heat of fusion, and centrifugal force are important in determining areas requiring protection. Droplet size is the critical parameter for determining chordwise extent of areas requiring ice protection.
F-1
Appendix F
TABLE F-1. CHECKLIST (Continued)
Influence Consideration
b. Where the propeller ice protection system consumes power from the electrical system, pneumatic system, or bleed air system, a load analysis should be provided showing that the power source capacity is adequate to provide ice protection in addition to all other essential loads.
c. Where fluid is required for ice protection, a limitation should be placed in the AFM on flight in icing conditions to prevent exhausting the fluid prior to exiting the icing condition. Sufficient margin in fluid capacity should be maintained to allow for alternate airport landing in accordance with operational requirements.
d. Other specific areas of concern include:
(1) The effect of deicer boot installation upon propeller blade and cuff, and hub structural integrity.
(2) Surface temperature.
(3) Timer or other control system reliability.
(4) Spinner ice accumulation.
e. Perform tests to verify that ice sheds from the blades and to demonstrate compliance with § 23.1301(d) and § 23.1419(a) and (b). During testing, verify that adequate ice protection is provided, propeller performance degradations are not excessive, vibration characteristics are satisfactory and ice being shed is small enough to avoid detrimental damage to other aircraft components. Tests should include examination of the structural integrity of the propeller assembly and associated equipment with ice protection (heater blankets, slip rings, wiring, and so forth) installed.
4. Equipment, Systems, Function, and Installation
a. Conduct a study as discussed in paragraph 9e (failure analysis) of this AC to assure that no probable failure or malfunction of any power source (electrical, fluid, bleed air, pneumatic, and so forth) will impair the ability of the remaining source(s) to supply adequate power to systems essential to safe operation during icing flight.
b. Conduct a power source load analysis to verify proper power requirements are provided.
c. Verify that power source failure warning is provided to the crew.
F-2
Appendix F
TABLE F-1. CHECKLIST (Continued)
Influence Consideration
d. Demonstrate that the alternator or generator is protected from detrimental ice accumulation.
e. Determine if load shedding can be accomplished after a partial failure condition. If applicable, a load shedding sequence should be provided so the pilot may assure that adequate power is available to the ice protection equipment and other necessary equipment for flight in icing conditions.
f. Determine that maximum windshield heat does not adverse affect structural integrity or pilot view.
5. Circuit and Protective Devices
a. Determine that the design incorporates electrical overload protection that opens regardless of operating control position.
b. Verify that the design is such that no protective device is protecting more than one circuit essential to continued safe flight (for example, pitot heat and stall warning transducer heat are considered separate essential circuits and should be provided separate protection). Ice protection monitor and warning circuits should be considered separate from control circuits and each should provide individual circuit protection. On airplanes equipped with dual power sources, a power distribution system having a single bus and a single circuit breaker protecting the ice protection system is not acceptable.
6. Airfoil Leading Edge Protection System
a. Provide a means to indicate to the crew that the ice protection system is receiving adequate electrical power, bleed air pressure, vacuum, or fluid, and so forth, as appropriate, and it is functioning normally.
b. Conduct droplet trajectory and impingement analysis of wing, and horizontal and vertical stabilizers to establish aft limits for ice formation.
Areas of concern include adequacy of upper and lower limits of wing and stabilizer protection to allow safe flight in icing conditions.
c. The maintenance manual should contain approved cleaning, surface treatment, and repair procedures for leading edge ice protection systems.
F-3
Appendix F
TABLE F-1. CHECKLIST (Continued)
Influence Consideration
d. Analyses and testing required for replacement-deicing systems are dependent on the certification basis of the project and the deicing system material and design characteristics. See Appendix E for guidance.
7. Static Pressure System
a. Each static port design or location should be such that correlation between air pressure in the static system and true ambient pressure is not altered when flying in icing conditions. Means of showing compliance include the following: anti-icing devices, alternate source for static pressure, or demonstration by test that port icing does not occur under any condition.
b. Where the port is thermally protected, a thermal evaluation should be conducted to demonstrate that the protection is adequate.
8. Pitot, Static, Angle-of- Attack, and Stall Warning Sensors
a. Provide analysis (thermal analysis in the case of heated pitot tube and static ports) to establish anti-icing/deicing requirements.
b. Perform tests to verify analyses and demonstrate compliance. Use these verified analyses to extrapolate to the critical conditions of part 25, Appendix C. Several combinations of parameters may be critical test points.
For unprotected components, testing may be conducted to demonstrate that airspeed, altitude, and other indications remain within acceptable tolerances under the critical conditions. In some cases, adequate bench and flight testing may already have been accomplished on other airplanes to establish an approval basis by similarity on a specific airplane.
9. Magnetic Direction Designs should minimize Magnetic Direction Indicator (MDI) deviations; however, if MDI deviations greater than ±10 degrees exist when operating electrical ice protection equipment, provide placarding.
F-4
Appendix F
TABLE F-1. CHECKLIST (Continued)
Influence Consideration NOTE 7 If the ice protection system causes greater than an l0-degree deviation, then § 23.1327 (amendment 23-20) should be applied in lieu of previous requirements.
The one exception is single-side Electronic Flight Information Systems (EFIS) installations in which the safety assessment uses magnetic heading as a backup. A policy to address this is being added in AC 23-17A.
10. Ice Inspection Light(s)
a. Night flight evaluation of light coverage and glare produced by the wing ice inspection light(s) should be evaluated.
b. A hand-held flashlight is not acceptable as an ice detection light.
c. The ice detection light(s) should be evaluated in icing conditions to verify that sufficient illumination is provided for the pilot to detect ice accumulation.
11. Antennas and Other Components
a. Conduct structural analysis to establish that critical ice build-ups on antennas, masts, and other components attached externally to the airplane do not result in hazards.
b. Tests in natural icing or with simulated ice shapes may be used to substantiate the structural analysis.
c. Ice shedding from these components should be evaluated to verify that size and trajectory do not damage other parts of the airplane.
12. Fluid Systems
a. Certain fluids used in ice protection systems are flammable.
Components of these systems must meet the flammable fluid protection requirements of § 23.863. No components of these systems may be installed in passenger or crew compartments without the protection required by § 23.853(d) (prior to amendment 23-34) or § 23.853(e) (after amendment 23-34).
F-5
Appendix F
TABLE F-1. CHECKLIST. (Continued)
Influence Consideration
b. Fluid capacity should be established based on the operational capability of the airplane and on the ability to fly to an alternate airport and safely land. Means should be provided to monitor fluid capacity and flow rates as they relate to flight. The method for determining ice protection availability should be provided in the operating procedures of the AFM.
c. The maintenance manual should list approved fluids and, if pilot and crewmembers are required to replace fluids, these approved fluids should be listed in the AFM. The fluid filler inlet should bear a placard stating that only approved fluids be used. Approved fluids may be listed on this placard or in the AFM.
d. The compatibility of the fluid with airframe and engine components should be examined to verify that adverse reactions such as corrosion or contamination do not occur, or are prevented through inspection or other measures (for example, if ethylene glycol is a component fluid, then silver and silver-plated electrical switch contacts and terminals should be protected from contamination by the ethylene glycol to avoid a fire hazard).
13. Flight Tests The certification rules require analyses and tests to demonstrate that the airplane can safely operate in the icing envelope of part 25, Appendix C.
Compliance can be determined by similarities to previously approved configurations. If it should be necessary to conduct dry air tests with ice shapes, natural icing tests, or simulated icing tests, the goals and results should be in accordance with the guidance provided in Sections 11 and 12 of this AC.
14. Flight Manual and Placards The AFM and appropriate placards in the airplane should be designed to provide the pilot with sufficient information to safely operate the airplane in an icing environment.
F-6
Appendix G
APPENDIX G. PART 23 SUBPART B TESTS FOR SECTION 23.1419 AT AMENDMENT 23-43
TABLE G-1. PART 23 SUBPART B TESTS FOR SECTION 23.1419 AT AMENDMENT 23-43
Regulation 14 CFR Section
Guidance Proof of compliance
23.21 Only critical weight and CG loadings, as determined during the noncontaminated airplane tests, are required. Natural icing flight tests may be accomplished at a nominal CG.
Load distribution limits
23.23 Only critical weight and CG loadings, as determined during the noncontaminated airplane tests, are required. Tests in which lateral load is critical, such as stall characteristics, should include tests with maximum allowable fuel asymmetry.
There should not be different load, weight, and CG limits for flight in icing. Operation in icing conditions should be essentially transparent to the flightcrew in that no icing-specific methods of operation (other than activating ice protection systems) should be required. This philosophy is also based on human factors issues to reduce operational complexity and flightcrew workload.
General (Performance)
23.45 Must comply, except performance should be determined up to a temperature of standard plus five degrees C instead of plus 30 degrees C. It can be assumed that ice accretion will not be present on the airframe at temperatures warmer than plus five degrees C. For deicing systems, the average drag increment and propeller efficiency determined over the deicing cycle may be used for performance calculations. Propeller deicing codes do not address propeller runback icing. Similarity to previously flight-tested configurations or qualitative performance evaluations in natural icing should be accomplished.
Stall speed 23.49 Must comply with critical ice accretions. See paragraph 12a(1)(c) for exemption considerations to the 61-knot stall speed requirement. Stall speeds with critical ice accretions should be determined and published in the AFM.
Takeoff speeds
23.51 When determining the takeoff speeds V1, VR, and V2 for flight in icing conditions, the values of VMCG and VMC determined for non-icing conditions may be used.
G-1
Appendix G
TABLE G-1. PART 23 SUBPART B TEST FOR SECTION 23.1419 AT AMENDMENT 23-43 (Continued)
Regulation 14 CFR Section
Guidance
Takeoff speeds (Cont'd)
23.51 (Cont'd) If the stall speed with “takeoff” ice at maximum takeoff weight with takeoff flaps, gear retracted exceeds that in non-icing conditions by more than the greater of three KCAS or three percent VS1, the speed at 50 feet or V2 must be increased to remain compliant.
Takeoff performance
23.53 The effect of operating ice protection systems on engine performance should be accounted for.
Takeoff performance in icing conditions must be calculated with “takeoff” ice if:
a. The stall speed with “takeoff” ice at maximum takeoff weight with takeoff flaps, gear retracted exceeds that in non-icing conditions by more than the greater of three KCAS or three percent VS1; and
b. If commuter category, the degradation of the gradient of climb determined in accordance with § 23.67(c)(2) is greater than onehalf of the applicable actual-to-net takeoff path gradient reduction defined in § 25.61(b); and
c. If multi-engine normal, utility or acrobatic category, the degradation of the gradient of climb determined in accordance with § 23.67(a) or (b) is greater than one-half of the applicable actual-tonet takeoff path gradient reduction defined in § 25.61(b).
Acceleratestop distance
23.55 Applicable for commuter category only. The effect of any increase due to takeoff in icing conditions may be determined by analysis.
Takeoff path 23.57
Takeoff distance and takeoff run
23.59 Applicable for icing for commuter category only if the conditions described above in 23.53 are met. May be calculated by a suitable analysis.
Takeoff flight path
23.61 Climb:
general
23.63 Must be compliant, except ambient temperatures above 41-degrees F do not need to be addressed.
G-2