measurements should determine the effect on fatigue life due to ice accumulation for such items as main rotor blades, main rotor hub components, rotating and fixed controls, horizontal stabilizer, tail rotor, etc. The subsequent proper operation of retractable devices such as landing gear should be demonstrated with representative ice accretion. In addition, the static and fatigue strength of the blade with heater mat should be substantiated. Any effect of the heater mat on fatigue strength of the blades should be considered.
(3) Additional Considerations. The following are items to consider in an icing certification program. They are not intended to be all-inclusive, and the possibility of widely differing characteristics and critical areas among various rotorcraft in icing should be considered.
(i) The rotorcraft should be shown by analysis and confirmed by either simulated or natural icing tests to be capable of holding for 30 minutes in the design conditions of the continuous maximum icing envelope at the most critical weight, CG, and altitude with a fully functional ice protection system.
(i) A single ice protection system and power source may be considered acceptable provided that after any single failure of the ice protection system, the rotorcraft can be shown by analysis and/or test to be capable of safe operation (no hazard) for 15 minutes following failure recognition in the continuous icing envelope used as the basis for certification within the same icing limits used for the 30-minute hold criteria. During this 15-minute period the rotorcraft may exhibit degraded characteristics. Pilot controllable operating limitations such as airspeed may be used to satisfy this continued safe flight criteria. For purposes of determining performance and handling qualities degradation, ice protection system failure need not be considered to occur simultaneously with engine failure unless ice protection system operation is dependent upon engine operation.
Although current airborne weather radar technology systems may be useful in avoiding potential icing conditions by detecting precipitation, the use of weather radar is not an FAA/AUTHORITY requirement for icing certification.
(Iv) § 27.1419(e) says there must be a means to advise the crew when the rotorcraft is in icing conditions in order that the system may be activated.
(v) No autorotational performance data is required for rotorcraft which have Category A powerplant installations. The rotorcraft must be capable of full autorotational landings with the ice protection system operating (§ 27.143a(2) (vi).
Autorotational entry, steady state, and flare entry flying qualities and performance should be evaluated with the ice load to be expected with the deice system operating and with the ice load to be expected 15 minutes after failure of the system. Since the en route performance can vary as the ice protection system operates, a mean value of cyclic torque is acceptable provided, at no time the power required drops below that par 693 913
АС 27-1A 7/30/97 required for level flight. The rotorcraft is assumed to be clear of ice prior to takeoff, and, therefore, the takeoff performance is not degraded. The landing performance can be based on the in-flight assessment of overall performance degradation. Items such as fuel burns can be used as part of the in-flight performance degradation determination.
Regardless of the methods used to determine performance degradation, they must be easily used by the crew. The hover performance should be addressed for the termination of a flight after an icing encounter. The engines should be protected from the adverse effects of ice. When ice does accumulate on the inlets, screens, etc., it must be accounted for in performance, engine operating characteristics, and inlet distortion.
(vi) The handling qualities of the rotorcraft must be substantiated if ice can accumulate on any surface. When ice can accumulate on unprotected surfaces, the rotorcraft must exhibit satisfactory IFR handling qualities. In addition, following the failure of the deice system, the rotorcraft must be safely controllable for 15 minutes, i.e., the rotorcraft must be free from excessive and rapid divergence. Artificial ice shapes may be acceptable for acquisition of flight test data necessary for handling qualities and performance evaluations and demonstrations.
(vii) Items such as fuel tank vents, cooling vents, antennas, etc., should be substantiated for maximum icing effects.
(vill) The ice protection system should be sufficiently reliable to perform its intended function in accordance with the requirements of § 27.1309. These requirements may in some instances be met by the use of sound engineering judgment during design and compliance demonstrations. In many instances, use of good design practices, failure modes and effects analysis, and similarity analyses combined with good judgment will be adequate. In some instances the need for reliability analyses may be desirable. Additional information pertaining to reliability is contained in Paragraph 621 (§ 27.1309) of this AC.
(ix) The subject of lightning should be addressed. The criteria applied on rotorcraft with ice protection systems are that "the rotorcraft should be protected in such a manner to minimize lightning risk. The general rules of § 27.1309(a), (b), and (c) are applicable to ensure adequate lightning protection. (Amendment 27-21, November 6, 1984, added lightning protection requirements in § 27.610.)
(x) Ice protection of pitot-static sources, windshields, inlets, exposed control linkages, etc., should be considered.
(xi) The impact of ice protection system failure, complete and partial, and achieving adequate warning thereof should be assessed.
(xii) The impact of delayed application of ice protection systems should be assessed. Hazardous conditions should not be apparent. Any rotorcraft characteristic 914 Par 693
changes resulting should be covered in cautionary material in the rotorcraft flight manual.
(xili) Possible droop stop malfunction with ice accumulation and its potential hazard to the rotorcraft, its occupants, and ground personnel should be assessed.
(xiv) Possible ice shedding hazards to ground personnel or equipment in proximity to turning rotors following flight in icing conditions should be given consideration.
(4) Flight Manual. Areas of the flight manual which may require input are:
(i) Operating limitations including approved types of operation and prohibiting operation in freezing rain or freezing drizzle conditions. Avoidance procedures may also be useful.
(il) Normal Operating Procedures. Information on the ice detection means or system and ice protection system and their capabilities.
(ill) Emergency Operating Procedures. Operating procedures containing essential information particularly with system failure.
(iv) Caution Notes. These caution notes should advise or address:
(A) Against inducing asymmetric shedding with rapid control inputs or rotor speed changes, except possibly as a last resort. Rotor speed changes appear to be more effective than control inputs in removing ice from the rotor blades of some rotorcraft.
(B) Loss in range, climb rate, and hover capability following prolonged operation in icing.
(C) The need for clean blade surfaces and use of approved cleaning solvents or ground deicing/anti-icing agents prior to start of rotors turning.
(D) Changes in autorotational characteristics resulting from ice formations.
(E) Although the rotorcraft has been certificated for flight in supercooled clouds and falling and blowing snow, flight in other conditions such as freezing rain, freezing drizzle, sleet, hail, and combinations of these conditions with supercooled clouds must be avoided.
Par 693 915
(F) The potential hazards to ground personnel, passengers deplaning, and equipment in proximity to turning rotors following flight in icing conditions.
d. Icing References.
(1) FAA Technical Report ADS-4, Engineering Summary of Airframe Icing Technical Data, December 1963.
(2) Advisory Circular 20-73, Aircraft Ice Protection, 21 April 71.
(3) Advisory Circular 91-51, Airplane Deice and Anti-ice Systems, 9/15/77.
(4) FAA Report RD-77-76, Engineering Summary of Powerplant Icing Technical Data, July 1977.
(5) United States Army Aviation Engineering Flight Activity Reports:
(i> Natural Icing Tests, UH-1H Helicopter, Final Report, June 1974, USAASTA Project No. 74-31.
(ii) Artificial Icing Tests, UH-1H Helicopter, Part 1, Final Report, January 1974, USAASTA Project No. 73-04-4.
(ili) Artificial Icing Tests, UH-1H Helicopter, Part II, Heated Glass Windshield, Final Report, USAASTA Project No. 73-04-4.
(iv) Artificial Icing Tests, Lockheed Advanced Ice Protection System Installed on a UH-1H Helicopter, Final Report, June 1975, USAAEFA Project No. 74-13.
(v) Artificial and Natural Icing Tests for Qualification of the UH-1H, Kit A Aircraft, Letter Report, USAAEFA Project No. 78-21-1.
(vi) Microphysical Properties of Artificial and Natural Clouds and Their Effects on UH-1H Helicopter Icing, Report USAAEFA Project No. 78-21-2.
(vii) Helicopter Icing Spray System (HISS) Nozzle Improvement Evaluation, Final Report, September 1981, USAAEFA Project No. 79-002-2.
(vili) Artificial and Natural Icing Tests of the YCH-4TD, Final Report, May 1981, USAAEFA Project No. 79-07.
(ix) Limited Artificial Icing Tests of the OV-ID, Letter Report, July 1981, USAAEFA Project No. 80-16, (Limited Distribution).
916 Par 693
(x) JUH-IH Ice Phobic Coating Tests, Final Report, July 1980, USAAEFA Project No. 79-02.
(xi) Artificial and Natural Icing Tests, Production UH-60A Helicopter, Final Report, June 1980, USAAEFA Project No. 79-19.
(xii) Helicopter Icing Spray System (HISS) Evaluation and Improvements, Letter Report, June 1981, USAAEFA Project No. 80-04.
(xiii) Artificial Icing Test of CH-47C Helicopter with Fiberglass Rotor Blades, Final Report, July 1979, USAAEFA Project No. 78-18.
(xiv) Limited Artificial and Natural Icing Tests, Production UH-60A Helicopter (Reevaluation), Final Report, August 1981, USAAEFA Project No. 80-14.
(6) Further Icing Experiments on an Unheated Nonrotating Cylinder, National Research Council, Canada Report LTR-LT-105, dated November 1979, by J.R. Sta labrass and P.F. Hearty.
(7) Ludlam, F.H., Heat Economy of a Rimed Cylinder, Quarterly Journal, Royal Meteorological Society, Vol. 77, 1951.
(8) U.S. Army AMRDL Reports:
USAAMRDL TR 73-38, Ice Protection Investigation For Advanced Rotary Wing Aircraft, J.B. Werner, August 1973, AD 7711182.
Werner, J.B., The Development of an Advanced Anti-Icing/Deicing Capability for U.S. Army Helicopters, Volume 1, Design Criteria and Technology Considerations, USAAMRDL - TR-75-34A, Eustis Directorate, U.S. Army Air Mobility R&D Laboratory, November 1975, AD A019044.
(iii) Werner, J.B., The Development of an Advanced Anti-Icing/Deicing Capability for U.S. Army Helicopters, Volume 2, Ice Protection System Application to the UH-1H Helicopter, USAAMRDL - TR-75-34B, Eustis Directorate, U.S. Army Air Mobility Research and Development Laboratory, November 1975, AD A019049.
(iv) USAAMRDL-TR-76-32, Ottawa Spray Rig Tests of an Ice Protection System Applied to the UH-1H Helicopter, November 1976, AD A0034458.
(v) USARTL-TR-78-48, Icing Tests of a UH-1H Helicopter with an Electrothermal Ice Protection System Under Simulated and Natural Icing Conditions, April 1979.
Par 693 917
(vi) USAAMRDL-TR77-36, Final Report, Natural Icing Flights and Additional Simulated Icing Tests of a UH-IH Helicopter Incorporating an Electrothermal Ice Protection System, July 1978, AD A059704.
(9) Technical Feasibility Test of Ice Phobic Coatings for Rain Erosion in Simulated Flight Conditions, U.S. Army Test and Evaluation Command, Final Report, 4-AI-192-IPS-001, August 1980.
(10) Technical Feasibility Test of Ice Phobic Coatings in Simulated Icing Flight Conditions, U.S. Army TECOM, Final Report, 4-CO-160-000-048, September 1980.
(11) Aircraft Icing, NASA Conference Publication 2086, FAA-RD-78-109, July 1978.
Helicopter Icing Review, FAA Technical Center, Final Report, FAA-CT-80-210, September 1980.
National Icing Facilities Requirements Investigation, Final Report, FAA Technical Center, FAA-CT-81-35, March 1981.
(14) Aircraft Icing, AGARD Advisory Report No. 127, November 1978.
(15) Rotorcraft Icing - Review and Prospects, AGARD Advisory Report, AR-166, September 1981.
(16) Advisory Circular 20-117, Hazards Following Ground Deicing and Ground Operations in Conditions Conducive to Aircraft Icing, Dec. 17, 1982.
(17) Olson, W., Experimental Comparison of Icing Cloud Instruments, January 1983, NASA TM 83340.
(18) JUH-1H Redesigned Pneumatic Boot Deicing System Flight Test Evaluation. Hayworth, L., Graham, M., August 1987. USAAEFA Edwards AFB, California. Project No. 83-13.
(19) An Appraisal of the Single Rotating Cylinder Method of Liquid Water Content Measurement, National Research Council Canada Report LTR-LT-92, dated November 1978, by J.R. Stallabrass.
918 Par 693
40 - 30 20 - 10 0 - -10 2000 4000 6000 8000 10,000
PRESSURE ALTITUDE - FT FIGURE 693-1. CONTINUOUS ICING - TEMPERATURE VS ALTITUDE LIMITS Figures 693-1 through 4 represent the approach to a 10,000-foot altitude limit. See Paragraph b(5) (iii) for a discussion on this approach.
Par 693 919
АС 27-1A 7/30/97 40 30 AMBIENT TEMPERATURE - DEG F 20 - 10 -
• - -10 2000 4000 6000 8000 10,000
PRESSURE ALTITUDE - FT FIGURE 693-2. INTERMITTENT ICING - TEMPERATURE VS ALTITUDE LIMITS Figures 693-1 through 4 represent the approach to a 10,000-foot altitude limit.
See Paragraph b(5)(iii) for a discussion on this approach.
920 Par 693
1.0 - LIQUID WATER CONTENT - GRAMS/CUBIC METER 0.8 SEA LEVEL TO 10,000 FT PRESSURE ALTITUDE
0.6 AMBIENT TEMP °F
0.4
0.2 10 20 30 40 50
MEAN EFFECTIVE DROP DIAMETER - MICRONS FIGURE 693-3. CONTINUOUS ICING-LIQUID WATER CONTENT VS. DROP DIAMETER Figures 693-1 through 4 represent one approach to a 10,000-foot altitude limit.
See Paragraph b(5) (iii) for a discussion of this approach.
921 Par 693
2.0 SEA LEVEL TO 10,000 FT PRESSURE ALTITUDE LIQUID WATER CONTENT - GRAMS/CUBIC METER 1.6 AMBIENT TEMP
- 32 °F
1.2
- 14 °F
0.8
- 0 °F
0.4 10 20 30 40 50
MEAN EFFECTIVE DROP DIAMETER - MICRONS FIGURE 693-4. INTERMITTENT ICING-LIQUID WATER CONTENT VS DROP DIAMETER Figures 693-1 through 4 represent one approach to a 10,000-foot altitude limit.
See paragraph b(5)(iii) for a discussion of this approach.
922 Par 693
694.-700. RESERVED.
Intentionally Left Blank Par 694 923 (thru 929)
701. RESERVED.
Intentionally Left Blank 930 Par 701