AMC 25.21(g) Performance and handling characteristics in icing conditions

ED Decision 2018/005/R

Table of Contents

Para.    Title

1            Purpose

2            Related Requirements

3            Reserved

4            Requirements and Guidance

4.1        General

4.2        Proof of Compliance (CS 25.21(g))

4.3        Propeller Speed and Pitch Limits (CS 25.33)

4.4        Performance - General (CS 25.101)

4.5        Stall Speed (CS 25.103)

4.6        Failure Conditions (CS 25.1309)

4.7        Flight-related Systems

4.8        Aeroplane Flight Manual (CS 25.1581)

5            Acceptable Means of Compliance - General

5.1        General

5.2        Flight Testing

5.3        Wind Tunnel Testing and Analysis

5.4        Engineering Simulator Testing and Analysis

5.5        Engineering Analysis

5.6        Ancestor Aeroplane Analysis

6            Acceptable Means of Compliance - Flight Test Programme

6.1        General

6.2        Stall Speed (CS 25.103)

6.3        Accelerate-stop Distance (CS 25.109)

6.4        Take-off Path (CS 25.111)

6.5        Landing Climb: All-engines-operating (CS 25.119)

6.6        Climb: One-engine-inoperative (CS 25.121)

6.7        En-route Flight Path (CS 25.123)

6.8        Landing (CS 25.125)

6.9        Controllability and Manoeuvrability - General (CS 25.143)

6.10     Longitudinal Control (CS 25.145)

6.11     Directional and Lateral Control (CS 25.147)

6.12     Trim (CS 25.161)

6.13     Stability - General (CS 25.171)

6.14     Demonstration of Static Longitudinal Stability (CS 25.175)

6.15     Static Directional and Lateral Stability (CS 25.177)

6.16     Dynamic Stability (CS 25.181)

6.17     Stall Demonstration (CS 25.201)

6.18     Stall Warning (CS 25.207)

6.19     Wind Velocities (CS 25.237)

6.20     Vibration and Buffeting (CS 25.251)

6.21     Natural Icing Conditions

6.22     Failure Conditions (CS 25.1309)

A1         Appendix 1 - Airframe Ice Accretion

A1.1     General

A1.2     Operative Ice Protection System

A1.3     Ice Protection System Failure Cases

A1.4     Additional guidance for Appendix O ice accretions

A2         https://dxweb.easa.europa.eu/dx4/Topics/Cloned-908a3904-6301-4e9d-a841-79c1efdc07c0.docx - Artificial Ice Shapes

A2.1     General

A2.2     Shape and Texture of Artificial Ice

A2.3     "Sandpaper Ice"

A3         Appendix 3 - Design Features

A3.1     Aeroplane Configuration and Ancestry

A3.2     Wing

A3.3     Empennage

A3.4     Aerodynamic Balancing of Flight Control Surfaces

A3.5     Ice Protection/Detection System

A4         Appendix 4 - Examples of Aeroplane Flight Manual Limitations and Operating Procedures for Operations    in Supercooled Large Drop Icing Conditions

A5         Appendix 5 - Related Acceptable Means of Compliance (AMC) and FAA Advisory Circulars (AC)

A6         Appendix 6 - Acronyms and definitions

1       Purpose.

1.1     This AMC describes an acceptable means for showing compliance with the requirements related to performance and handling characteristics of Large Aeroplanes as affected by flight in icing conditions. The means of compliance described in this AMC is intended to provide guidance to supplement the engineering and operational judgement that should form the basis of any compliance findings relative to handling characteristics and performance in Appendix C and Appendix O icing conditions.

1.2     The guidance information is presented in sections 4 to 6 and three appendices.

1.3     Section 4 explains the various performance and handling requirements in relation to the flight conditions that are relevant for determining the shape and texture of ice accretions for the aeroplane in the atmospheric icing conditions of CS-25, Appendix C and Appendix O.

1.4     Section 5 describes acceptable methods and procedures that an applicant may use to show that an aeroplane meets these requirements. Depending on the design features of a specific aeroplane as discussed in Appendix 3 of this AMC, its similarity to other types or models, and the service history of those types or models, some judgement will often be necessary for determining that any particular method or procedure is adequate for showing compliance with a particular requirement. AMC 25.1420(f) provides guidance for comparative analysis as an acceptable means of compliance to meet these requirements.

1.5     Section 6 provides an acceptable flight test programme where flight testing is selected by the applicant and agreed by the Agency as being the primary means of compliance.

1.6     The three appendices provide additional reference material associated with ice accretion, artificial ice shapes, and aeroplane design features.

2       Related Requirements. The following paragraphs of CS-25 are related to the guidance in this AMC:

—          CS 25.21 (Proof of compliance)

—          CS 25.103 (Stall speed)

—          CS 25.105 (Take-off)

—          CS 25.107 (Take-off speeds)

—          CS 25.111 (Take-off path)

—          CS 25.119 (Landing climb)

—          CS 25.121 (Climb: One-engine-inoperative)

—          CS 25.123 (En-route flight paths)

—          CS 25.125 (Landing)

—          CS 25.143 (Controllability and Manoeuvrability - General)

—          CS 25.207 (Stall warning)

—          CS 25.237 (Wind velocities)

—          CS 25.253 (High-speed characteristics)

—          CS 25.1309 (Equipment, systems, and installations)

—          CS 25.1419 (Ice protection)

—          CS 25.1420 (Supercooled large drop icing conditions)

—          CS 25.1581 (Aeroplane Flight Manual)

—          CS-25, Appendix C

—          CS 25, Appendix O

3       Reserved.

4       Requirements and Guidance.

4.1     General. This section provides guidance for showing compliance with Subpart B requirements for flight in the icing conditions of Appendix C and Appendix O to CS-25.

4.1.1  Operating rules for commercial operation of large aeroplanes (e.g. Part-CAT¹, CAT.OP.MPA.250) require that the aeroplane is free of any significant ice contamination at the beginning of the take-off roll due to application of appropriate ice removal and ice protection procedures during flight preparation on the ground.

4.1.2  For certification for flight in the icing conditions described in Appendix C of CS-25, CS 25.21(g)(1) requires that an aeroplane meet certain performance and handling qualities requirements while operating in the icing environment defined in Appendix C. In addition, CS 25.1420 requires applicants to consider icing conditions beyond those covered by Appendix C. The additional icing conditions that must be considered are the supercooled large drop icing conditions defined in Appendix O. CS 25.21(g)(2) and (3) respectively provide the performance and handling qualities requirements to be met by applicants not seeking certification in the icing conditions of Appendix O and by applicants seeking certification in any portion of the icing conditions of Appendix O. Appendix 1 of this AMC provides detailed guidance for determining ice accretions in both Appendix C and Appendix O icing conditions that can be used for showing compliance.

CS 25.1420 requires applicants to choose to do one of the following:

(a)     Not seek approval for flight in the supercooled large drop atmospheric icing conditions defined in Appendix O.

(b)     Seek approval for flight in only a portion of Appendix O icing conditions.

(c)      Seek approval for flight throughout the entire Appendix O atmospheric icing envelope.

4.1.3  Because an aeroplane may encounter supercooled large drop icing conditions at any time while flying in icing conditions, certain safety requirements must be met for the supercooled large drop icing conditions of Appendix O, even if the aeroplane will not be certified for flight in the complete range of Appendix O atmospheric icing conditions. CS 25.21(g)(2) requires the stall speed (CS 25.103), landing climb (CS 25.119), and landing (CS 25.125) requirements to be met in supercooled large drop atmospheric icing conditions beyond those the aeroplane will be certified for. Compliance with these requirements plus the requirements for flight in Appendix C icing conditions are intended to provide adequate performance capability for a safe exit from all icing conditions after an encounter with supercooled large drop atmospheric icing conditions beyond those the aeroplane is certified for.

4.1.4  If the aeroplane is not to be certified for flight in all of the supercooled large drop icing conditions of Appendix O, there must be a means of indicating when the aeroplane has encountered icing conditions beyond those it is certified for. See AMC 25.1420 for guidance on acceptable means of detecting and indicating when the aeroplane has encountered icing conditions beyond those it is certified for. The applicant should provide procedures in the aeroplane flight manual to enable a safe exit from all icing conditions after an encounter with icing conditions beyond those the aeroplane is certified for.

4.1.5  To certify an aeroplane for operations in Appendix O icing conditions only for certain flight phase(s), the applicant should define the flight phase(s) for which approval is sought in a way that will allow a flight crew to easily determine whether the aeroplane is operating inside or outside its certified icing envelope. The critical ice accretion or accretions used to show compliance with the applicable requirements should cover the range of aeroplane configurations, operating speeds, angles-of-attack, and engine thrust or power settings that may be encountered during that phase of flight (not just at the conditions specified in the CS-25 subpart B requirements). For the ice accretion scenarios defined in paragraph A1.4.3(c) of Appendix 1 to this AMC, the applicable flight phases are take-off (including the ground roll, take-off, and final take-off segments), en route, holding, and approach/landing (including both the approach and landing segments).

4.1.6  Ice accretions used to show compliance with the applicable CS-25 subpart B regulations should be consistent with the extent of the desired certification for flight in icing conditions. Appendices C and O define the ice accretions, as a function of flight phase, that must be considered for certification for flight in those icing conditions. Any of the applicable ice accretions (or a composite accretion representing a combination of accretions) may be used to show compliance with a particular subpart B requirement if it is either the ice accretion identified in the requirement or one shown to be more conservative than that. In addition, the ice accretion with the most adverse effect on handling characteristics may be used for compliance with the aeroplane performance requirements if each difference in performance is conservatively taken into account. Ice accretion(s) used to show compliance should take into account the speeds, configurations (including configuration changes), angles of attack, power or thrust settings, etc. for the flight phases and icing conditions they are intended to cover. For example, if the applicant desires certification for flight in the supercooled large drop icing conditions of Appendix O in addition to those of Appendix C, compliance with the applicable subpart B requirements may be shown using the most critical of the Appendix C and Appendix O ice accretions.

4.1.7  Certification experience has shown that it is not necessary to consider ice accumulation on the propeller, induction system or engine components of an inoperative engine for handling qualities substantiation.  Similarly, the mass of the ice need not normally be considered.

4.1.8  Flight in icing conditions includes operation of the aeroplane after leaving the icing conditions, but with ice accretion remaining on the critical surfaces of the aeroplane.

4.1.9  Ice-contaminated tailplane stall (ICTS) refers to a phenomenon identified as a causal factor in several aeroplane incidents and accidents. It results from airflow separation on the lower surface of the tailplane because ice is present. ICTS can occur if the angle-of-attack of the horizontal tailplane exceeds its stall angle-of-attack. Even very small quantities of ice on the tailplane leading edge can significantly reduce the angle-of-attack at which the tailplane stalls. An increase in tailplane angle-of-attack, which may lead to a tailplane stall, can result from changes in aeroplane configuration (for example, extending flaps, which increases the downwash angle at the tail or the pitch trim required) or flight conditions (a high approach speed, gusts, or manoeuvring, for example). An ICTS is characterized by reduction or loss of pitch control or pitch stability while in, or soon after leaving, icing conditions. A flight test procedure for determining susceptibility to ICTS is presented in paragraph 6.9.4, Low g Manoeuvres and Sideslips, of this AMC.

(a)     For aeroplanes with unpowered longitudinal control systems, the pressure differential between the upper and lower surfaces of the stalled tailplane may result in a high elevator hinge moment, forcing the elevator trailing edge down. This elevator hinge moment reversal can be of sufficient magnitude to cause the longitudinal control (for example, the control column) to suddenly move forward with a force beyond the capability of the flight crew to overcome. On some aeroplanes, ICTS has been caused by a lateral flow component coming off the vertical stabilizer, as may occur in sideslip conditions or because of a wind gust with a lateral component.

(b)     Aerodynamic effects of reduced tailplane lift should be considered for all aeroplanes, including those with powered controls. Aeroplanes susceptible to this phenomenon are those having a near zero or negative tailplane stall margin with tailplane ice contamination.

4.1.10 There have been aeroplane controllability incidents in icing conditions as a result of ice on unprotected leading edges of extended trailing edge flaps or flap vanes. The primary safety concern illustrated by these incidents is the potential for controllability problems due to the accretion of ice on trailing edge flap or flap vane leading edges while extending flaps in icing conditions. The flight tests specified in Table 4 of this AMC, in which handling characteristics are tested at each flap position while ice is being accreted in natural icing conditions, are intended to investigate this safety concern. Unless controllability concerns arise from these tests, it is not necessary to conduct flight tests with artificial ice shapes on the extended trailing edge flap or flap vanes or to include extended trailing edge flap or flap vane ice accretions when evaluating aeroplane performance with flaps extended.

4.1.11 Supercooled large drop icing conditions, or runback ice in any icing condition, can cause a ridge of ice to form aft of the protected area on the upper surface of the wing. This can lead to separated airflow over the aileron. Ice-induced airflow separation upstream of the aileron can have a significant effect on aileron hinge moment. Depending on the extent of the separated flow and the design of the flight control system, ice accretion upstream of the aileron may lead to aileron hinge moment reversal, reduced aileron effectiveness, and aileron control reversal. Although aeroplanes with de-icing boots and unpowered aileron controls are most susceptible to this problem, all aeroplanes should be evaluated for roll control capability in icing conditions. Acceptable flight test procedures for checking roll control capability are presented in paragraphs 6.9.3, 6.15, and 6.17.2.e of this AMC and consist of bank-to-bank roll manoeuvres, steady heading sideslips, and rolling manoeuvres at stall warning speed.

4.1.12 Appendix 5 contains related Acceptable Means of Compliance and FAA Advisory Circulars. Appendix 6 contains acronyms and definitions used in this AMC.

4.2     Proof of Compliance (CS 25.21(g)).

4.2.1  Demonstration of compliance with certification requirements for flight in icing conditions may be accomplished by any of the means discussed in paragraph 5.1 of this AMC.

4.2.2  Certification experience has shown that aeroplanes of conventional design do not require additional detailed substantiation of compliance with the requirements of the following paragraphs of CS-25 for flight in icing conditions or with ice accretions:

25.23, Load distribution limits

25.25, Weight limits

25.27, Centre of gravity limits

25.29, Empty weight and corresponding centre of gravity

25.31, Removable ballast

25.231, Longitudinal stability and control

25.233, Directional stability and control

25.235, Taxiing condition

25.253(a) and (b), High-speed characteristics, and

25.255, Out-of-trim characteristics

4.2.3  Where normal operation of the ice protection system results in changing the stall warning system and/or stall identification system activation settings, it is acceptable to establish a procedure to return to the non icing settings when it can be demonstrated that the critical wing surfaces are free of ice accretion.

4.3     Propeller Speed and Pitch Limits (CS 25.33). Certification experience has shown that it may be necessary to impose additional propeller speed limits for operations in icing conditions.

4.4     Performance - General (CS 25.101).

4.4.1  The propulsive power or thrust available for each flight condition must be appropriate to the aeroplane operating limitations and normal procedures for flight in icing conditions. In general, it is acceptable to determine the propulsive power or thrust available by suitable analysis, substantiated when required by appropriate flight tests (e.g. when determining the power or thrust available after 8 seconds for CS 25.119). The following aspects should be considered:

a.       Operation of induction system ice protection.

b.      Operation of propeller ice protection.

c.       Operation of engine ice protection.

d.      Operation of airframe ice protection system.

4.4.2  The following should be considered when determining the change in performance due to flight in icing conditions:

a.       Thrust loss due to ice accretion on propulsion system components with normal operation of the ice protection system, including engine induction system and/or engine components, and propeller spinner and blades.

b.      The incremental airframe drag due to ice accretion with normal operation of the ice protection system.

c.       Changes in operating speeds due to flight in icing conditions.

4.4.3  Certification experience has shown that any increment in drag (or decrement in thrust) due to the effects of ice accumulation on the landing gear, propeller, induction system and engine components may be determined by a suitable analysis or by flight test.

4.4.4  Apart from the use of appropriate speed adjustments to account for operation in icing conditions, any changes in the procedures established for take-off, balked landing, and missed approaches should be agreed with the Agency.

4.4.5  Performance associated with flight in icing conditions is applicable after exiting icing conditions until the aeroplane critical surfaces are free of ice accretion and the ice protection systems are selected “Off.”

4.4.6  Certification experience has also shown that runback ice may be critical for propellers, and propeller analyses do not always account for it. Therefore, runback ice on the propeller should be addressed. Research has shown that ice accretions on propellers, and resulting thrust decrement, may be larger in Appendix O (supercooled large drop) icing conditions than in Appendix C icing conditions for some designs. This may be accomplished through aeroplane performance checks in natural icing conditions, icing tanker tests, icing wind tunnel tests, aerodynamic analysis, or the use of an assumed (conservative) loss in propeller efficiency. Testing should include a range of outside air temperatures, including warmer (near freezing) temperatures that could result in runback icing. For the Appendix O icing conditions, the applicant may use a comparative analysis. AMC 25.1420(f) provides guidance for comparative analysis.

4.5     Stall speed (CS 25.103). Certification experience has shown that for aeroplanes of conventional design it is not necessary to make a separate determination of the effects of Mach number on stall speeds for the aeroplane with ice accretions.

4.6     Failure Conditions (CS 25.1309).

4.6.1  The failure modes of the ice protection system and the resulting effects on aeroplane handling and performance should be analysed in accordance with CS 25.1309. In determining the probability of a failure condition, it should be assumed that the probability of entering icing conditions defined in CS-25 Appendix C is one. As explained in AMC 25.1420, on an annual basis, the average probability of encountering the icing conditions defined in Appendix O may be assumed to be 1 × 10_-2 per flight hour. This probability should not be reduced on a phase-of-flight basis. The "Failure Ice" configuration is defined in Appendix 1, paragraph A1.3.

4.6.2  For probable failure conditions that are not annunciated to the flight crew, the guidance in this AMC for a normal condition is applicable with the "Failure Ice" configuration.

4.6.3  For probable failure conditions that are annunciated to the flight crew, with an associated procedure that does not require the aeroplane to exit icing conditions, the guidance in this AMC for a normal condition is applicable with the "Failure Ice" configuration.

4.6.4  For probable failure conditions that are annunciated to the flight crew, with an associated operating procedure that requires the aeroplane to leave the icing conditions as soon as possible, it should be shown that the aeroplane’s resulting performance and handling characteristics with the failure ice accretion are commensurate with the hazard level as determined by a system safety analysis in accordance with CS 25.1309. The operating procedures and related speeds may restrict the aeroplane’s operating envelope, but the size of the restricted envelope should be consistent with the safety analysis.

4.6.5  For failure conditions that are extremely remote but not extremely improbable, the analysis and substantiation of continued safe flight and landing, in accordance with CS 25.1309, should take into consideration whether annunciation of the failure is provided and the associated operating procedures and speeds to be used following the failure condition.

4.7     Flight-related Systems. In general, systems aspects are covered by the applicable systems and equipment requirements in other subparts of CS-25, and associated guidance material.  However, certification experience has shown that other flight related systems aspects should be considered when determining compliance with the flight requirements of subpart B.  For example, the following aspects may be relevant:

a.       The ice protection systems may not anti-ice or de-ice properly at all power or thrust settings. This may result in a minimum power or thrust setting for operation in icing conditions which affects descent and/or approach capability. The effect of power or thrust setting should also be considered in determining the applicable ice accretions. For example, a thermal bleed air system may be running wet resulting in the potential for runback ice.

b.       Ice blockage of control surface gaps and/or freezing of seals causing increased control forces, control restrictions or blockage.

c.       Airspeed, altitude and/or angle of attack sensing errors due to ice accretion forward of the sensors (e.g. radome ice). Dynamic pressure ("q") operated feel systems using separate sensors also may be affected.

d.       Ice blockage of unprotected inlets and vents that may affect the propulsive thrust available, aerodynamic drag, powerplant control, or flight control.

e.       Operation of stall warning and stall identification reset features for flight in icing conditions, including the effects of failure to operate.

f.       Operation of icing condition sensors, ice accretion sensors, and automatic or manual activation of ice protection systems.

g.       Flight guidance and automatic flight control systems operation. See AMC No. 1 and 2 to 25.1329 for guidance on compliance with CS 25.1329 for flight in icing conditions, including stall and manoeuvrability evaluations with the aeroplane under flight guidance system control.

h.       Installed thrust. This includes operation of ice protection systems when establishing acceptable power or thrust setting procedures, control, stability, lapse rates, rotor speed margins, temperature margins, Automatic Take-Off Thrust Control System (ATTCS) operation, and power or thrust lever angle functions.

4.8     Aeroplane Flight Manual (CS 25.1581).

4.8.1  Limitations.

4.8.1.1 Where limitations are required to ensure safe operation in icing conditions, these limitations should be stated in the AFM.

4.8.1.2 The Limitations section of the AFM should include, as applicable, a statement similar to the following: “In icing conditions the aeroplane 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."

4.8.1.3 For aeroplanes without leading edge high-lift devices, unless an acceptable means exists to ensure that the protected surfaces of the wing leading edges are free of ice contamination immediately prior to take-off, the wing ice protection system should be operative and efficient before take-off (at least during the final taxi phase) whenever the outside air temperature is below 6°C (42 °F) and any of the following applies:

—          Visible moisture is present in the air or on the wing,

—                   The difference between the dew point temperature and the outside air temperature is less than 3°C (5 °F), or

—                   Standing water, slush, ice, or snow is present on taxiways or runways.

An acceptable means to ensure that the wing leading edges are free of ice contamination immediately prior to take-off would be the application of anti-icing fluid with adequate hold over time and compliant with SAE AMS 1428, Types II, III, or IV.

Note: The aircraft must be de-iced in compliance with applicable operational rules.

4.8.1.4 To comply with CS 25.1583(e), Kinds of operation, the AFM Limitations section should clearly identify the extent of each approval to operate in icing conditions, including the extent of any approval to operate in the supercooled large drop atmospheric icing conditions defined in CS-25 Appendix O.

4.8.1.5 For aeroplanes not certified to operate throughout the atmospheric icing envelope of CS-25 Appendix O for every flight phase, the Limitations section of the AFM should also identify the means for detecting when the certified icing conditions have been exceeded and state that intentional flight, including take-off and landing, into these conditions is prohibited. A requirement to exit all icing conditions must be included if icing conditions for which the aeroplane is not certified are encountered.

4.8.2  Operating Procedures.

4.8.2.1 AFM operating procedures for flight in icing conditions should include normal operation of the aeroplane including operation of the ice protection system and operation of the aeroplane following ice protection system failures. Any changes in procedures for other aeroplane system failures that affect the capability of the aeroplane to operate in icing conditions should be included.

4.8.2.2 Normal operating procedures provided in the AFM should reflect the procedures used to certify the aeroplane for flight in icing conditions.  This includes configurations, speeds, ice protection system operation, power plant and systems operation, for take-off, climb, cruise, descent, holding, go-around, and landing. For aeroplanes not certified for flight in all of the supercooled large drop atmospheric icing conditions defined in Appendix O to CS-25, procedures should be provided for safely exiting all icing conditions if the aeroplane encounters Appendix O icing conditions that exceed the icing conditions the aeroplane is certified for. Information to be provided in the AFM may be based on the information provided in the reference fleet AFM(s), or other operating manual(s) furnished by the TC holder, when comparative analysis is used as the means of compliance.

4.8.2.3 For aeroplanes without leading edge high-lift devices, the AFM normal operating procedures section should contain a statement similar to the following:

“WARNING

Minute amounts of ice or other contamination on the leading edges or wing upper surfaces can result in a stall without warning, leading to loss of control on take-off.”

4.8.2.4 Abnormal operating procedures should include the procedures to be followed in the event of annunciated ice protection system failures and suspected unannunciated failures. Any changes to other abnormal procedures contained in the AFM, due to flight in icing conditions, should also be included.

4.8.3  Performance Information. Performance information, derived in accordance with subpart B of CS-25, must be provided in the AFM for all relevant phases of flight.

4.8.4  Examples of AFM limitations and operating procedures are contained in Appendix 4 of this AMC.

5       Acceptable Means of Compliance - General.

5.1     General.

5.1.1  This section describes acceptable methods and procedures that an applicant may use to show that an aeroplane meets the performance and handling requirements of subpart B in the atmospheric conditions of Appendix C and Appendix O to CS-25.

5.1.2  Compliance with CS 25.21(g) should be shown by one or more of the methods listed in this section.

5.1.3  The compliance process should address all phases of flight, including take-off, climb, cruise, holding, descent, landing, and go-around as appropriate to the aeroplane type, considering its typical operating regime and the extent of its certification approval for operation in the atmospheric icing conditions of Appendix O to CS-25.

5.1.4  The design features included in Appendix 3 of this AMC should be considered when determining the extent of the substantiation programme.

5.1.5  Appropriate means for showing compliance include the actions and items listed in Table 1 below. These are explained in more detail in the following sections of this AMC.

TABLE 1: Means for Showing Compliance

5.1.6  Various factors that affect ice accretion on the airframe with an operative ice protection system and with ice protection system failures are discussed in Appendix 1 of this AMC.

5.1.7  An acceptable methodology to obtain agreement on the artificial ice shapes is given in Appendix 2 of this AMC. That appendix also provides the different types of artificial ice shapes to be considered.

5.2     Flight Testing.

5.2.1  General.

5.2.1.1 The extent of the flight test programme should consider the results obtained with the non-contaminated aeroplane and the design features of the aeroplane as discussed in Appendix 3 of this AMC.

5.2.1.2 It is not necessary to repeat an extensive performance and flight characteristics test programme on an aeroplane with ice accretion. A suitable programme that is sufficient to demonstrate compliance with the requirements can be established from experience with aeroplanes of similar size, and from review of the ice protection system design, control system design, wing design, horizontal and vertical stabiliser design, performance characteristics, and handling characteristics of the non-contaminated aeroplane. In particular, it is not necessary to investigate all weight and centre of gravity combinations when results from the non-contaminated aeroplane clearly indicate the most critical combination to be tested.  It is not necessary to investigate the flight characteristics of the aeroplane at high altitude (i.e. above the highest altitudes specified in Appendix C and Appendix O to CS-25). An acceptable flight test programme is provided in section 6 of this AMC.

5.2.1.3 Certification experience has shown that tests are usually necessary to evaluate the consequences of ice protection system failures on handling characteristics and performance and to demonstrate continued safe flight and landing.

5.2.2  Flight Testing Using Approved Artificial Ice Shapes.

5.2.2.1 The performance and handling tests may be based on flight testing in dry air using artificial ice shapes that have been agreed with the Agency.

5.2.2.2 Additional limited flight tests are discussed in paragraph 5.2.3, below.

5.2.3  Flight Testing In Natural Icing Conditions.

5.2.3.1 Where flight testing with ice accretion obtained in natural atmospheric icing conditions is the primary means of compliance, the conditions should be measured and recorded. The tests should ensure good coverage of CS-25 Appendix C and Appendix O conditions (consistent with the extent of the certification approval sought for operation in Appendix O icing conditions) and, in particular, the critical conditions. The conditions for accreting ice (including the icing atmosphere, configuration, speed and duration of exposure) should be agreed with the Agency.

5.2.3.2 Where flight testing with artificial ice shapes is the primary means of compliance, additional limited flight tests should be conducted with ice accretion obtained in natural icing conditions. The objective of these tests is to corroborate the handling characteristics and performance results obtained in flight testing with artificial ice shapes. As such, it is not necessary to measure the atmospheric characteristics (i.e. liquid water content (LWC) and median volumetric diameter (MVD)) of the flight test icing conditions. For some derivative aeroplanes with similar aerodynamic characteristics as the ancestor, it may not be necessary to carry out additional flight test in natural icing conditions if such tests have been already performed with the ancestor. Depending on the extent of the Appendix O icing conditions that certification is being sought for, and the means used for showing compliance with the performance and handling characteristics requirements, it may also not be necessary to conduct flight tests in the natural icing conditions of Appendix O. See AMC 25.1420 for guidance on when it is necessary to conduct flight tests in the natural atmospheric icing conditions of Appendix O.

5.3     Wind Tunnel Testing and Analysis. Analysis of the results of dry air wind tunnel testing of models with artificial ice shapes, as defined in Part II of Appendix C and Appendix O to CS-25, may be used to substantiate the performance and handling characteristics.

5.4     Engineering Simulator Testing and Analysis. The results of an engineering simulator analysis of an aeroplane that includes the effects of the ice accretions as defined in Part II of Appendix C and Appendix O to CS-25 may be used to substantiate the handling characteristics. The data used to model the effects of ice accretions for the engineering simulator may be based on results of dry air wind tunnel tests, flight tests, computational analysis, and engineering judgement.

5.5     Engineering Analysis. An engineering analysis that includes the effects of the ice accretions as defined in Part II of Appendix C and Appendix O to CS-25 may be used to substantiate the performance and handling characteristics. The effects of the ice shapes used in this analysis may be determined by an analysis of the results of dry air wind tunnel tests, flight tests, computational analysis, engineering simulator analysis, and engineering judgement.

5.6     Ancestor Aeroplane Analysis.

5.6.1  To help substantiate acceptable performance and handling characteristics, the applicant may use an analysis of an ancestor aeroplane that includes the effect of the ice accretions as defined in Part II of Appendix C and Appendix O to CS-25. This analysis should consider the similarity of the configuration, operating envelope, performance and handling characteristics, and ice protection system of the ancestor aeroplane to the one being certified.

5.6.2  The analysis may include flight test data, dry air wind tunnel test data, icing tunnel test data, engineering simulator analysis, service history, and engineering judgement.

5.7     Comparative Analysis.

                   For showing compliance with the CS-25 certification specifications relative to SLD icing conditions represented by Appendix O, the applicant may use a comparative analysis. AMC 25.1420 (f) provides guidance for comparative analysis.

6       Acceptable Means of Compliance - Flight Test Programme.

6.1     General.

6.1.1  This section provides an acceptable flight test programme where flight testing is selected by the applicant and agreed by the Agency as being the primary means for showing compliance.

6.1.2  Where an alternate means of compliance is proposed for a specific paragraph in this section, it should enable compliance to be shown with at least the same degree of confidence as flight test would provide (see CS 25.21(a)(1)).

6.1.3  Ice accretions for each flight phase are defined in Part II of Appendix C and Part II of Appendix O to CS-25. Additional guidance for determining the applicable ice accretions is provided in Appendix 1 to this AMC.

6.1.4  This test programme is based on the assumption that the applicant will choose to use the holding Ice accretion for the majority of the testing assuming that it is the most conservative ice accretion. In general, the applicant may choose to use an ice accretion that is either conservative or is the specific ice accretion that is appropriate to the particular phase of flight. In accordance with Part II of Appendix C and Part II(e) of Appendix O to CS-25, if the holding ice accretion is not as conservative as the ice accretion appropriate to the flight phase, then the ice accretion appropriate to the flight phase (or a more conservative ice accretion) must be used.

6.1.5  For the approach and landing configurations, in accordance with the guidance provided in paragraph 4.1.10 of this AMC, the flight tests in natural icing conditions specified in Table 4 of this AMC are usually sufficient to evaluate whether ice accretions on trailing edge flaps adversely affect aeroplane performance or handling qualities. If these tests show that aeroplane performance or handling qualities are adversely affected, additional tests may be necessary to show compliance with the aeroplane performance and handling qualities requirements.

6.2     Stall Speed (CS 25.103).

6.2.1  The stall speed for intermediate high lift configurations can normally be obtained by interpolation. However if a stall identification system (e.g. stick pusher) activation point is set as a function of the high lift configuration and/or the activation point is reset for icing conditions, or if significant configuration changes occur with extension of trailing edge flaps (such as wing leading edge high-lift device position movement), additional tests may be necessary.

6.2.2  Acceptable Test Programme. The following represents an acceptable test programme subject to the provisions outlined above:

a.       Forward centre of gravity position appropriate to the configuration.

b.      Normal stall test altitude.

c.       In the configurations listed below, trim the aeroplane at an initial speed of 1.13 to 1.30 V_SR. Decrease speed at a rate not to exceed 0.5 m/sec² (1 knot per second) until an acceptable stall identification is obtained.

i.        High lift devices retracted configuration, "Final Take-off Ice."

ii.       High lift devices retracted configuration, "En-route Ice."

iii.      Holding configuration, "Holding Ice."

iv.      Lowest lift take-off configuration, "Holding Ice."

v.       Highest lift take-off configuration, "Take-off Ice."

vi.      Highest lift landing configuration, "Holding Ice."

6.3     Accelerate-stop Distance (CS 25.109). The effect of any increase in V1 due to take-off in icing conditions may be determined by a suitable analysis.

6.4     Take-off Path (CS 25.111). If VSR in the configuration defined by CS 25.121(b) with the “Take-off Ice" accretion defined in Appendix C and Appendix O to CS-25 exceeds VSR for the same configuration without ice accretions by more than the greater of 5.6 km/h (3 knots) or 3%, the take-off demonstrations should be repeated to substantiate the speed schedule and distances for take-off in icing conditions.  The effect of the take-off speed increase, thrust loss, and drag increase on the take-off path may be determined by a suitable analysis.

6.5     Landing Climb: All-engines-operating (CS 25.119). Acceptable Test Programme. The following represents an acceptable test programme:

a.       The "Holding Ice" accretion should be used.

b.       Forward centre of gravity position appropriate to the configuration.

c.       Highest lift landing configuration, landing climb speed no greater than VREF.

d.       Stabilise at the specified speed and conduct 2 climbs or drag polar checks as agreed with the Agency.

6.6     Climb: One-engine-inoperative (CS 25.121). Acceptable Test Programme. The following represents an acceptable test programme:

a.       Forward centre of gravity position appropriate to the configuration.

b.       In the configurations listed below, stabilise the aeroplane at the specified speed with one engine inoperative (or simulated inoperative if all effects can be taken into account) and conduct 2 climbs in each configuration or drag polar checks substantiated for the asymmetric drag increment as agreed with the Agency.

i.        High lift devices retracted configuration, final take-off climb speed, "Final Take-off Ice."

ii.       Lowest lift take-off configuration, landing gear retracted, V₂ climb speed, "Take-off Ice."

iii.      Approach configuration appropriate to the highest lift landing configuration, landing gear retracted, approach climb speed, "Holding Ice."

6.7     En-route Flight Path (CS 25.123). Acceptable Test Programme. The following represents an acceptable test programme:

a.       The "En-route Ice" accretion should be used.

b.       Forward centre of gravity position appropriate to the configuration.

c.       En-route configuration and climb speed.

d.       Stabilise at the specified speed with one engine inoperative (or simulated inoperative if all effects can be taken into account) and conduct 2 climbs or drag polar checks substantiated for the asymmetric drag increment as agreed with the Agency.

6.8     Landing (CS 25.125). The effect of landing speed increase on the landing distance may be determined by a suitable analysis.

6.9     Controllability and Manoeuvrability - General (CS 25.143 and 25.177).

6.9.1  A qualitative and quantitative evaluation is usually necessary to evaluate the aeroplane's controllability and manoeuvrability. In the case of marginal compliance, or the force limits or stick force per g limits of CS 25.143 being approached, additional substantiation may be necessary to establish compliance. In general, it is not necessary to consider separately the ice accretion appropriate to take-off and en-route because the "Holding Ice" is usually the most critical.

6.9.2  General Controllability and Manoeuvrability. The following represents an acceptable test programme for general controllability and manoeuvrability, subject to the provisions outlined above:

a.       The "Holding Ice" accretion should be used.

b.      Medium to light weight, aft centre of gravity position, symmetric fuel loading.

c        In the configurations listed in Table 2, trim at the specified speeds and conduct the following manoeuvres:

i.        30° banked turns left and right with rapid reversals;

ii.       Pull up to 1.5g (except that this may be limited to 1.3g at V_REF), and pushover to 0.5g (except that the pushover is not required at V_MO and V_FE); and

iii.      Deploy and retract deceleration devices.

TABLE 2: Trim Speeds

V_{SR —} Reference Stall Speed

V_{MO —} Maximum operating limit speed

IAS _— Indicated air speed

V_{FE —} Maximum flap extended speed

V_{REF —} Reference landing speed

d.      Lowest lift take-off configuration: At the greater of 1.13 V_SR or V₂ MIN, with the critical engine inoperative (or simulated inoperative if all effects can be taken into account), conduct 30° banked turns left and right with normal turn reversals and, in wings-level flight, a 9.3 km/h (5 knot) speed decrease and increase.

e.       Conduct an approach and go-around with all engines operating using the recommended procedure.

f.       Conduct an approach and go-around with the critical engine inoperative (or simulated inoperative if all effects can be taken into account) using the recommended procedure.

g.       Conduct an approach and landing using the recommended procedure. In addition satisfactory controllability should be demonstrated during a landing at V_REF minus 9.3 km/h (5 knots). These tests should be done at heavy weight and forward centre of gravity.

h.      Conduct an approach and landing with the critical engine inoperative (or simulated inoperative if all effects can be taken into account) using the recommended procedure.

6.9.3  Evaluation of Lateral Control Characteristics. Aileron hinge moment reversal and other lateral control anomalies have been implicated in icing accidents and incidents. The following manoeuvre, along with the evaluation of lateral controllability during a deceleration to the stall warning speed covered in paragraph 6.17.2(e) of this AMC and the evaluation of static lateral-directional stability covered in paragraph 6.15 of this AMC, is intended to evaluate any adverse effects arising from both stall of the outer portion of the wing and control force characteristics.

For each of the test conditions specified in subparagraphs (a) and (b) below, perform the manoeuvres described in subparagraphs 1 through 6 below.

(a)     Holding configuration, holding ice accretion, maximum landing weight, forward centre-of-gravity position, minimum holding speed (highest expected holding angle-of-attack); and

(b)     Landing configuration, most critical of holding, approach, and landing ice accretions, medium to light weight, forward centre-of-gravity position, V_REF (highest expected landing approach angle-of-attack).

1        Establish a 30-degree banked level turn in one direction.

2        Using a step input of approximately 1/3 full lateral control deflection, roll the aeroplane in the other direction.

3        Maintain the control input as the aeroplane passes through a wings level attitude.

4        At approximately 20 degrees of bank in the other direction, apply a step input in the opposite direction to approximately 1/3 full lateral control deflection.

5        Release the control input as the aeroplane passes through a wings level attitude.

6        Repeat this test procedure with 2/3 and up to full lateral control deflection unless the roll rate or structural loading is judged excessive.  It should be possible to readily arrest and reverse the roll rate using only lateral control input, and the lateral control force should not reverse with increasing control deflection.

6.9.4  Low g Manoeuvres and Sideslips. The following represents an example of an acceptable test program for showing compliance with controllability requirements in low g manoeuvres and in sideslips to evaluate susceptibility to ice-contaminated tailplane stall.

6.9.4.1 CS 25.143(i)(2) states: “It must be shown that a push force is required throughout a pushover manoeuvre down to zero g or the lowest load factor obtainable if limited by elevator power or other design characteristic of the flight control system. It must be possible to promptly recover from the manoeuvre without exceeding a pull control force of  222 N. (50 lbf).

6.9.4.2 Any changes in force that the pilot must apply to the pitch control to maintain speed with increasing sideslip angle must be steadily increasing with no force reversals, unless the change in control force is gradual and easily controllable by the pilot without using exceptional piloting skill, alertness, or strength. Discontinuities in the control force characteristic, unless so small as to be unnoticeable, would not be considered to meet the requirement that the force be steadily increasing. A gradual change in control force is a change that is not abrupt and does not have a steep gradient that can be easily managed by a pilot of average skill, alertness, and strength. Control forces in excess of those permitted by CS 25.143(c) would be considered excessive.

(See paragraph 6.15.1 of this AMC for lateral-directional aspects).

6.9.4.3 The test manoeuvres described in paragraphs 6.9.4.1 and 6.9.4.2, above, should be conducted using the following configurations and procedures:

a.       The "Holding Ice" accretion should be used. For aeroplanes with unpowered elevators, these tests should also be performed with "Sandpaper Ice."

b.       Medium to light weight, the most critical of aft or forward centre of gravity position, symmetric fuel loading.

c.       In the configurations listed below, with the aeroplane in trim, or as nearly as possible in trim, at the specified trim speed, perform a continuous manoeuvre (without changing trim) to reach zero g normal load factor or, if limited by elevator control authority, the lowest load factor obtainable at the target speed.

i.        Highest lift landing configuration at idle power or thrust, and the more critical of:

—         Trim speed 1.23 V_SR, target speed not more than 1.23 V_SR, or

—         Trim speed V_FE, target speed not less than V_FE - 37 km/h (20 knots)

ii.       Highest lift landing configuration at go-around power or thrust, and the more critical of:

—         Trim speed 1.23 V_SR, target speed not more than 1.23 V_SR, or

—         Trim speed V_FE, target speed not less than V_FE - 37 km/h (20 knots)

d.       Conduct steady heading sideslips to full rudder authority, 801 N. (180 lbf) rudder force or full lateral control authority (whichever comes first), with highest lift landing configuration, trim speed 1.23 V_SR, and power or thrust for -3° flight path angle.

6.9.5  Controllability prior to Activation and Normal Operation of the Ice Protection System. The following represents an acceptable test programme for compliance with controllability requirements with the ice accretion prior to activation and normal operation of the ice protection system.

In the configurations, speeds, and power settings listed below, with the ice accretion specified in the requirement, trim the aeroplane at the specified speed. Conduct pull up to 1.5g and pushover to 0.5g without longitudinal control force reversal.

i.        High lift devices retracted configuration (or holding configuration if different), holding speed, power or thrust for level flight.

ii.       Landing configuration, V_REF for non-icing conditions, power or thrust for landing approach (limit pull up to stall warning).

6.10   Longitudinal Control (CS 25.145).

6.10.1 No specific quantitative evaluations are required for demonstrating compliance with CS 25.145(b) and (c). Qualitative evaluations should be combined with the other testing. The results from the non-contaminated aeroplane tests should be reviewed to determine whether there are any cases where there was marginal compliance. If so, these cases should be repeated with ice.

6.10.2 Acceptable Test Programme. The following represents an acceptable test programme for compliance with CS 25.145(a):

a.       The "Holding ice" accretion should be used.

b.      Medium to light weight, aft centre of gravity position, symmetric fuel loading.

c.       In the configurations listed below, trim the aeroplane at 1.3 V_SR.  Reduce speed using elevator control to stall warning plus one second and demonstrate prompt recovery to the trim speed using elevator control.

i.        High lift devices retracted configuration, maximum continuous power or thrust.

ii.       Maximum lift landing configuration, maximum continuous power or thrust.

6.11   Directional and Lateral Control (CS 25.147). Qualitative evaluations should be combined with the other testing. The results from the non-contaminated aeroplane tests should be reviewed to determine whether there are any cases where there was marginal compliance. If so, these cases should be repeated with ice.

6.12   Trim (CS 25.161).

6.12.1 Qualitative evaluations should be combined with the other testing. The results from the non-contaminated aeroplane tests should be reviewed to determine whether there are any cases where there was marginal compliance. If so, these cases should be repeated with ice. In addition a specific check should be made to demonstrate compliance with CS 25.161(c)(2).

6.12.2 The following represents a representative test program for compliance with 25.161(c)(2).

a.       The "Holding ice" accretion should be used.

b.      Most critical landing weight, forward centre of gravity position, symmetric fuel loading.

c.       In the configurations below, trim the aircraft at the specified speed.

i.        Maximum lift landing configuration, landing gear extended, and the most critical of:

—         Speed 1.3V_SR1 with Idle power or thrust; or,

—         Speed V_REF with power or thrust corresponding to a 3 deg glidepath'

6.13   Stability - General (CS 25.171). Qualitative evaluations should be combined with the other testing.  Any tendency to change speed when trimmed or requirement for frequent trim inputs should be specifically investigated.

6.14   Demonstration of Static Longitudinal Stability (CS 25.175).

6.14.1 Each of the following cases should be tested. In general, it is not necessary to test the cruise configuration at low speed (CS 25.175(b)(2)) or the cruise configuration with landing gear extended (CS 25.175(b)(3)); nor is it necessary to test at high altitude. The maximum speed for substantiation of stability characteristics in icing conditions (as prescribed by CS 25.253(c)) is the lower of 556 km/h (300 knots) CAS, V_FC, or a speed at which it is demonstrated that the airframe will be free of ice accretion due to the effects of increased dynamic pressure.

6.14.2 Acceptable Test Programme. The following represents an acceptable test programme for demonstration of static longitudinal stability:

a.       The "Holding ice" accretion should be used.

b.      High landing weight, aft centre of gravity position, symmetric fuel loading.

c.       In the configurations listed below, trim the aeroplane at the specified speed. The power or thrust should be set and stability demonstrated over the speed ranges as stated in CS 25.175(a) through (d), as applicable.

i.        Climb:  With high lift devices retracted, trim at the speed for best rate-of-climb, except that the speed need not be less than 1.3 VSR.

ii.       Cruise: With high lift devices retracted, trim at V_MO or 463 km/h (250 knots) CAS, whichever is lower.

iii.      Approach: With the high lift devices in the approach position appropriate to the highest lift landing configuration, trim at 1.3 V_SR.

iv.      Landing: With the highest lift landing configuration, trim at 1.3V_SR.

6.15   Static Directional and Lateral Stability (CS 25.177).

6.15.1 Compliance should be demonstrated using steady heading sideslips to show compliance with directional and lateral stability. The maximum sideslip angles obtained should be recorded and may be used to substantiate a crosswind value for landing (see paragraph 6.19 of this AMC).

6.15.2 Acceptable Test Programme. The following represents an acceptable test programme for static directional and lateral stability:

a.       The "Holding ice" accretion should be used.

b.      Medium to light weight, aft centre of gravity position, symmetric fuel loading.

c.       In the configurations listed below, trim the aeroplane at the specified speed and conduct steady heading sideslips to full rudder authority, 801 N. (180 lbf) rudder pedal force, or full lateral control authority, whichever comes first.

i.        High lift devices retracted configuration:  Trim at best rate-of-climb speed, but need not be less than 1.3 V_SR.

ii.       Lowest lift take-off configuration:  Trim at the all-engines-operating initial climb speed.

iii.      Highest lift landing configuration:  Trim at V_REF.

6.16   Dynamic Stability (CS 25.181). Provided that there are no marginal compliance aspects with the non-contaminated aeroplane, it is not necessary to demonstrate dynamic stability in specific tests. Qualitative evaluations should be combined with the other testing. Any tendency to sustain oscillations in turbulence or difficulty in achieving precise attitude control should be investigated.

6.17   Stall Demonstration (CS 25.201).

6.17.1 Sufficient stall testing should be conducted to demonstrate that the stall characteristics comply with the requirements. In general, it is not necessary to conduct a stall programme which encompasses all weights, centre of gravity positions (including lateral asymmetry), altitudes, high lift configurations, deceleration device configurations, straight and turning flight stalls, power off and power on stalls. Based on a review of the stall characteristics of the non-contaminated aeroplane, a reduced test matrix can be established. However, additional testing may be necessary if:

—         the stall characteristics with ice accretion show a significant difference from the non-contaminated aeroplane,

—         testing indicates marginal compliance, or

—         a stall identification system (e.g. stick pusher) is required to be reset for icing conditions.

6.17.2 Acceptable Test Programme. Turning flight stalls at decelerations greater than 1 knot/sec are not required.  Slow decelerations (much slower than 1 knot/sec) may be critical on aeroplanes with anticipation logic in their stall protection system or on aeroplanes with low directional stability, where large sideslip angles could develop. The following represents an acceptable test programme subject to the provisions outlined above.

a.       The "Holding ice" accretion should be used.

b.      Medium to light weight, aft centre of gravity position, symmetric fuel loading.

c.       Normal stall test altitude.

d.      In the configurations listed below, trim the aeroplane at the same initial stall speed factor used for stall speed determination. For power-on stalls, use the power setting as defined in CS 25.201 (a)(2) but with ice accretions on the aeroplane. Decrease speed at a rate not to exceed 1 knot/sec to stall identification and recover using the same test technique as for the non-contaminated aeroplane.

i.        High lift devices retracted configuration: Straight/Power Off, Straight/Power On, Turning/Power Off, Turning/Power On.

ii.       Lowest lift take-off configuration: Straight/Power On, Turning/Power Off.

iii.      Highest lift take-off configuration: Straight/Power Off, Turning/Power On.

iv.      Highest lift landing configuration: Straight/Power Off, Straight/Power On, Turning/Power Off, Turning/Power On.

e.       For the configurations listed in paragraph 6.17.2(d)i and iv, and any other configuration if deemed more critical, in 1 knot/second deceleration rates down to stall warning with wings level and power off, roll the aeroplane left and right up to 10 degrees of bank using the lateral control.

6.18   Stall Warning (CS 25.207).

6.18.1 Stall warning should be assessed in conjunction with stall speed testing and stall demonstration testing (CS 25.103, CS 25.201 and paragraphs 6.2 and 6.17 of this AMC, respectively) and in tests with faster entry rates.

6.18.2 Normal Ice Protection System Operation. The following represents an acceptable test programme for stall warning in slow down turns of at least 1.5g and at entry rates of at least 1 m/sec² (2 knot/sec):

a.       The "Holding ice" accretion should be used.

b.      Medium to light weight, aft centre of gravity position, symmetric fuel loading.

c.       Normal stall test altitude.

d.      In the configurations listed below, trim the aeroplane at 1.3V_SR with the power or thrust necessary to maintain straight level flight. Maintain the trim power or thrust during the test demonstrations.  Increase speed as necessary prior to establishing at least 1.5g and a deceleration of at least 1 m/sec² (2 knot/sec). Decrease speed until 1 sec after stall warning and recover using the same test technique as for the non-contaminated aeroplane.

i.        High lift devices retracted configuration;

ii.       Lowest lift take-off configuration; and

iii.      Highest lift landing configuration.

6.18.3 Ice Accretion Prior to Activation and Normal System Operation. The following represent acceptable means for evaluating stall warning margin with the ice accretion prior to activation and normal operation of the ice protection system.

a.       In the configurations listed below, with the ice accretion specified in the requirement, trim the aeroplane at 1.3 V_SR.

i.        High lift devices retracted configuration: Straight/Power Off.

ii.       Landing configuration: Straight/Power Off.

b.      At decelerations of up to 0.5 m/sec² (1 knot per second), reduce the speed to stall warning plus 1 second, and demonstrate that stalling can be prevented using the same test technique as for the non-contaminated aeroplane, without encountering any adverse characteristics (e.g., a rapid roll-off). As required by CS 25.207(h)(3)(ii), where stall warning is provided by a different means than for the aeroplane without ice accretion, the stall characteristics must be satisfactory and the delay must be at least 3 seconds.

6.19   Wind Velocities (CS 25.237).

6.19.1 Crosswind landings with "Landing Ice" should be evaluated on an opportunity basis.

6.19.2 The results of the steady heading sideslip tests with “Landing Ice” may be used to establish the safe cross wind component. If the flight test data show that the maximum sideslip angle demonstrated is similar to that demonstrated with the non-contaminated aeroplane, and the flight characteristics (e.g. control forces and deflections) are similar, then the non-contaminated aeroplane crosswind component is considered valid.

6.19.3 If the results of the comparison discussed in paragraph 6.19.2, above, are not clearly similar, and in the absence of a more rational analysis, a conservative analysis based on the results of the steady heading sideslip tests may be used to establish the safe crosswind component. The crosswind value may be estimated from:

V_CW = V_{REF  *} sin (sideslip angle) / 1.5

Where:

V_CW      is the crosswind component,

V_REF    is the landing reference speed appropriate to a minimum landing weight, and sideslip angle is that demonstrated at V_REF (see paragraph 6.15 of this AMC).

6.20   Vibration and Buffeting (CS 25.251).

6.20.1 Qualitative evaluations should be combined with the other testing, including speeds up to the maximum speed obtained in the longitudinal stability tests (see paragraph 6.14 of this AMC).

6.20.2 It is also necessary to demonstrate that the aeroplane is free from harmful vibration due to residual ice accumulation.  This may be done in conjunction with the natural icing tests.

6.20.3 An aeroplane with pneumatic de-icing boots should be evaluated to V_DF/M_DF with the de-icing boots operating and not operating.  It is not necessary to do this demonstration with ice accretion.

6.21   Natural Icing Conditions.

6.21.1 General.

6.21.1.1 Whether the flight testing has been performed with artificial ice shapes or in natural icing conditions, additional limited flight testing described in this section should be conducted in natural icing conditions specified in Appendix C to CS-25 and, if necessary, in the icing conditions described in Appendix O to CS-25. (AMC 25.1420 provides guidance on when it is necessary to perform flight testing in the atmospheric icing conditions of Appendix O.) Where flight testing with artificial ice shapes is the primary means for showing compliance, the objective of the tests described in this section is to corroborate the handling characteristics and performance results obtained in flight testing with artificial ice shapes.

6.21.1.2 It is acceptable for some ice to be shed during the testing due to air loads or wing flexure, etc.  However, an attempt should be made to accomplish the test manoeuvres as soon as possible after exiting the icing cloud to minimise the atmospheric influences on ice shedding.

6.21.1.3 During any of the manoeuvres specified in paragraph 6.21.2, below, the behaviour of the aeroplane should be consistent with that obtained with artificial ice shapes. There should be no unusual control responses or uncommanded aeroplane motions. Additionally, during the level turns and bank-to-bank rolls, there should be no buffeting or stall warning.

6.21.2 Ice Accretion/Manoeuvres.

6.21.2.1 Holding scenario.

a.       The manoeuvres specified in Table 3, below, should be carried out with the following ice accretions representative of normal operation of the ice protection system:

i.        On unprotected Parts: A thickness of 75 mm (3 inches) on those parts of the aerofoil where the collection efficiency is highest should be the objective. (A thickness of 50 mm (2 inches) is normally a minimum value, unless a lesser value is agreed by the Agency.)

ii.       On protected parts: The ice accretion thickness should be that resulting from normal operation of the ice protection system.

b.       For aeroplanes with control surfaces that may be susceptible to jamming due to ice accretion (e.g. elevator horns exposed to the air flow), the holding speed that is critical with respect to this ice accretion should be used.

Table 3: Holding Scenario – Manoeuvres

6.21.2.2 Approach/Landing Scenario. The manoeuvres specified in Table 4, below, should be carried out with successive accretions in different configurations on unprotected surfaces. Each test condition should be accomplished with the ice accretion that exists at that point. The final ice accretion (Test Condition 3) represents the sum of the amounts that would accrete during a normal descent from holding to landing in icing conditions.

TABLE 4: Approach/Landing Scenario – Manoeuvres

(*) The indicated thickness is that obtained on the parts of the unprotected aerofoil with the highest collection efficiency.

6.21.3 For aeroplanes with unpowered elevator controls, in the absence of an agreed substantiation of the criticality of the artificial ice shape used to demonstrate compliance with the controllability requirement, the pushover test of paragraph 6.9.4 should be repeated with a thin accretion of natural ice on the unprotected surfaces.

6.21.4 Existing propeller speed limits or, if required, revised propeller speed limits for flight in icing, should be verified by flight tests in natural icing conditions.

6.22   Failure Conditions (CS 25.1309).

6.22.1 For failure conditions which are annunciated to the flight crew, credit may be taken for the established operating procedures following the failure.

6.22.2 Acceptable Test Programme.  In addition to a general qualitative evaluation, the following test programme (modified as necessary to reflect the specific operating procedures) should be carried out for the most critical probable failure condition where the associated procedure requires the aeroplane to exit the icing condition:

a.       The ice accretion is defined as a combination of the following:

i.        On the unprotected surfaces - the “Holding ice” accretion described in paragraph A1.2.1 of this AMC;

ii.       On the normally protected surfaces that are no longer protected - the “Failure ice” accretion described in paragraph A1.3.2 of this AMC; and

iii.      On the normally protected surfaces that are still functioning following the segmental failure of a cyclical de-ice system – the ice accretion that will form during the rest time of the de-ice system following the critical failure condition.

b.      Medium to light weight, aft centre of gravity position, symmetric fuel loading.

c.       In the configurations listed below, trim the aeroplane at the specified speed. Conduct 30° banked turns left and right with normal reversals. Conduct pull up to 1.5g and pushover to 0.5g.

i.        High lift devices retracted configuration (or holding configuration if different): Holding speed, power or thrust for level flight.  In addition, deploy and retract deceleration devices.

ii.       Approach configuration: Approach speed, power or thrust for level flight.

iii.      Landing configuration: Landing speed, power or thrust for landing approach (limit pull up to 1.3g). In addition, conduct steady heading sideslips to angle of sideslip appropriate to type and landing procedure.

d.      In the configurations listed below, trim the aeroplane at estimated 1.3 V_SR Decrease speed to stall warning plus 1 second, and demonstrate prompt recovery using the same test technique as for the non-contaminated aeroplane. Natural stall warning is acceptable for the failure case.

i.        High lift devices retracted configuration: Straight/Power Off.

ii.       Landing configuration: Straight/Power Off.

e.       Conduct an approach and go-around with all engines operating using the recommended procedure.

f.       Conduct an approach and landing with all engines operating (unless the one-engine-inoperative condition results in a more critical probable failure condition) using the recommended procedure.

6.22.3 For improbable failure conditions, flight test may be required to demonstrate that the effect on safety of flight (as measured by degradation in flight characteristics) is commensurate with the failure probability or to verify the results of analyses and/or wind tunnel tests. The extent of any required flight test should be similar to that described in paragraph 6.22.2, above, or as agreed with the Agency for the specific failure condition.

[Amdt No: 25/3]

[Amdt No: 25/6]

[Amdt No: 25/13]

[Amdt No: 25/16]

[Amdt No: 25/18]

[Amdt No: 25/21]