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4.4.1 VSR in the configuration defined by § 25.121(b) with the takeoff ice accretion exceeding VSR for the same configuration without ice accretions by more than the greater of 3 knots or 3 percent.
4.4.2 Any need for a takeoff speed increase, and any effects of thrust loss or drag increase on the takeoff path, may be determined by a suitable analysis.
4.5 Landing Climb: All–Engines–Operating, § 25.119.
The following specifications represent an example of an acceptable test program for showing compliance with § 25.119.
Maneuvers
4.5.1 The holding ice accretion should be used.
4.5.2 The airplane should be loaded to a forward center-of-gravity position appropriate to the airplane configuration.
4.5.3 The airplane should be in the highest lift landing configuration, at a landing climb speed no greater than VREF.
4.5.4 Stabilize the airplane at the specified speed and conduct two climbs or drag polar checks as agreed to by the responsible ACO.
4.6 Climb: One-Engine-Inoperative, § 25.121.
The following specifications represent an example of an acceptable test program for showing compliance with § 25.121.
Maneuvers
4.6.1 The airplane should be loaded to a forward center-of-gravity position appropriate to the configuration.
4.6.2 Stabilize the airplane at the specified speed with one engine inoperative (or simulated inoperative if all relevant effects of an inoperative engine can be taken into account) and conduct two climbs or drag polar checks in each of the following airplane configurations, with the specified ice accretions, to substantiate the asymmetric drag increment as agreed to by the responsible ACO.
4.6.2.1 High lift devices retracted configuration, final takeoff climb speed—final takeoff ice.
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4.6.2.2 Lowest lift takeoff configuration, landing gear retracted, V2 climb speed— takeoff ice.
4.6.2.3 Approach configuration appropriate to the highest lift landing configuration, landing gear retracted, approach climb speed—holding ice.
4.7 En Route Flight Paths, § 25.123.
The following specifications represent an example of an acceptable test program to show compliance with § 25.123.
Maneuvers
4.7.1 The en route ice accretion should be used.
4.7.2 The airplane should be loaded to a forward center-of-gravity position appropriate to the airplane configuration.
4.7.3 The airplane should be in the en route configuration at the en route climb speed.
4.7.4 Stabilize the airplane at the specified speed with one engine inoperative (or simulated inoperative if all relevant effects of an inoperative engine can be taken into account) and conduct two climbs or drag polar checks to substantiate the asymmetric drag increment as agreed to by the responsible ACO.
4.8 Landing, § 25.125.
The effect of any landing speed increase on the landing distance may be determined by a suitable analysis.
4.9 Controllability and Maneuverability—General, § 25.143.
4.9.1 A qualitative and quantitative evaluation is usually necessary to show compliance with the controllability and maneuverability requirements of § 25.143. Depending on how clearly compliance is demonstrated, or whether the force limits or stick force per g limits of § 25.143 are being approached, additional substantiation may be necessary to ensure that the airplane complies.
4.9.2 Acceptable Test Program.
The following specifications represent an example of an acceptable test program to evaluate general controllability and maneuverability, subject to the provisions outlined above.
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Maneuvers
4.9.2.1 The holding ice accretion should be used.
4.9.2.2 The airplane should be loaded to a medium to light weight, with an aft center-of-gravity position, and symmetric fuel loading.
4.9.2.3 In the configurations listed in table 4-1 below, trim the airplane at the specified speeds and conduct the following maneuvers:
4.9.2.3.1 Thirty-degree banked turns left and right with rapid reversals.
4.9.2.3.2 A pull-up to 1.5 g (except that this may be limited to 1.3 g at VREF) and a pushover to 0.5 g (except that the pushover is not required at VMO and VFE).
4.9.2.3.3 Include deployment and retraction of deceleration devices.
Table 4-1. Controllability and Maneuverability—Trim Speeds Configuration Trim Speed High lift devices retracted configuration 1.3 VSR and VMO or 250 KIAS, whichever is less Lowest lift takeoff configuration 1.3 VSR and VFE or 250 KIAS, whichever is less Highest lift landing configuration VREF and VFE or 250 KIAS, whichever is less VSR – Reference Stall Speed VMO – Maximum operating limit speed KIAS – Knots indicated airspeed VFE – Maximum flap extended speed VREF – Reference landing speed
4.9.2.4 In the lowest lift takeoff configuration, at the greater of 1.13 VSR or V2MIN, with one engine inoperative (simulated), conduct 30° banked turns left and right with normal turn reversals and, in wings-level flight, a 5-knot speed decrease and increase.
4.9.2.5 Conduct an approach and go-around with all engines operating using the AFM approach and go-around procedure.
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4.9.2.6 Conduct an approach and go-around with one engine inoperative (simulated) using the AFM one-engine-inoperative approach and go-around procedure.
4.9.2.7 Conduct an approach and landing using the AFM approach and landing procedure. In addition, you should demonstrate satisfactory controllability during a landing at VREF minus 5 knots. These tests should be done at heavy weight and forward center-of-gravity.
4.9.2.8 Conduct an approach and landing with one engine inoperative (or with one engine simulated to be inoperative if all effects associated with an engine failure can be taken into account) using the procedure provided in the AFM.
4.9.3 Evaluation of Lateral Control Characteristics.
Aileron hinge moment reversal and other lateral control anomalies have been identified as causal factors in icing accidents and incidents. The following maneuvers, along with the following two evaluations, are intended to determine susceptibility of the airplane to aileron hinge moment reversals or other adverse effects on lateral control characteristics due to ice accretion.
E valuations
4.9.3.1 Evaluate lateral controllability during deceleration to the stall warning speed (covered in paragraph 4.17.2.5 of this AC), and
4.9.3.2 Evaluate static lateral-directional stability (covered in paragraph 4.15 of this AC).
Maneuvers
4.9.3.3 For each of the test conditions specified in table 4-2 below, Perform the following maneuvers:
4.9.3.3.1 Establish a 30° banked level turn in one direction.
4.9.3.3.2 Using a step input of approximately 1/3-full lateral control deflection, roll the airplane in the other direction.
4.9.3.3.3 Maintain the control input as the airplane passes through a wings level attitude.
4.9.3.3.4 At approximately 20° of bank, apply a step input in the opposite direction to approximately 1/3-full lateral control deflection.
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4.9.3.3.5 Release the control input as the airplane passes through a wings level attitude.
4.9.3.3.6 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.
Table 4-2. Test Conditions—Lateral Control Characteristics Test Condition 1 Holding configuration, holding ice accretion, maximum landing weight, forward center-of-gravity position, at minimum holding speed (highest expected holding angle-of-attack) 2 Landing configuration, holding ice accretion, medium to light weight, forward center-of-gravity position, at VREF (highest expected landing approach angle-of-attack)
4.9.4 Low g Maneuvers and Sideslips.
The maneuvers in paragraph 4.9.4.3 of this AC represent an example of an acceptable test program for showing compliance with controllability requirements in low g maneuvers and in sideslips to evaluate susceptibility to ice-contaminated tailplane stall.
4.9.4.1 Section 25.143(i)(2).
4.9.4.1.1 The regulation states: “It must be shown that a push force is required throughout a pushover maneuver down to a zero g load factor, or to 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 maneuver without exceeding a pull control force of 50 pounds….”
4.9.4.1.2 An example of another design characteristic of the flight control system that would limit the lowest obtainable load factor would be a g-limiting envelope protection system.
4.9.4.2 Section 25.143(i)(3).
4.9.4.2.1 For sideslips, the regulation requires that: “Any changes in force that the pilot must apply to the pitch control to maintain speed with increasing
4-24 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.” (See paragraph 4.15.1 of this AC for lateral-directional aspects).
4.9.4.2.2 Abrupt changes in the control force characteristic, unless so small as to be unnoticeable, would not be considered compliant with 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. It can be easily managed by a pilot of average skill, alertness, and strength. Control forces in excess of those permitted by § 25.143(d) would be considered excessive.
4.9.4.3 Test maneuvers used to show compliance with the regulatory requirements quoted in paragraphs 4.9.4.1.1 and 4.9.4.2.1 above should be conducted using the following ice accretions, configurations, and procedures:
Maneuvers
4.9.4.3.1 The holding ice accretion should be used. For airplanes with unpowered elevators, these tests should also be performed with sandpaper ice.
4.9.4.3.2 The airplane should be loaded to a medium to light weight, at the most critical center-of-gravity position, with symmetric fuel loading, and should be in the highest lift landing configuration.
4.9.4.3.3 Test maneuver for showing compliance with § 25.143(i)(2) is provided in table 4-3 below.
4-25 Table 4-3. Test Maneuver—§ 25.143(i)(2) Step Maneuver 1 Start with the airplane in trim, or as near as possible to being in trim, at the most critical of the following trim speeds:
(1) Trim speed 1.23 VSR, target speed not more than 1.23 VSR.
(2) Trim speed VFE, target speed not less than VFE - 20 knots.
2 Pull up to a suitable pitch attitude, then—
(1) Push over in a continuous maneuver (without changing trim) to reach zero g normal load factor or, if limited by elevator control authority (or other design characteristic), the lowest load factor obtainable at the target speed, as the airplane’s pitch attitude passes through approximately level flight (that is, through the horizon), and
(2) Perform this maneuver with idle power or thrust and with go-around power or thrust.
4.9.4.3.4 Test maneuver for showing compliance with § 25.143(i)(3): Conduct steady heading sideslips to full rudder input, 180 pounds rudder force, or full lateral control authority (whichever comes first) at a trim speed of
1.23 VSR and with the power or thrust needed for a -3° flight path angle.
4.9.5 Controllability Prior to Activation and Operation of the Ice Protection System.
The following is an example of an acceptable test program for showing compliance with § 25.25.143(j).
Maneuvers
4.9.5.1 For the configurations, speeds, and power settings listed below, with the ice accretion specified in the requirement, trim the airplane at the specified speed, conduct a pull-up maneuver to 1.5 g and pushover maneuver to
0.5 g, and show that longitudinal control forces do not reverse.
4.9.5.1.1 High lift devices retracted configuration (or holding configuration if different), holding speed, power or thrust for level flight.
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4.9.5.1.2 Landing configuration, VREF for non-icing conditions, power or thrust for landing approach. If necessary, limit the pull-up maneuver to the point at which stall warning occurs.
4.10 Longitudinal Control, § 25.145.
4.10.1 No specific quantitative evaluations are required for demonstrating compliance with§ 25.145(b) and (c). Qualitative evaluations should be combined with the other testing. Review results of tests on the uncontaminated airplane for any cases of marginal compliance. All tests showing marginal compliance should be repeated with ice accretions on the airplane.
4.10.2 Acceptable Test Program.
The following specifications represent an example of an acceptable test program for compliance with § 25.145(a).
Maneuvers
4.10.2.1 The holding ice accretion should be used.
4.10.2.2 The airplane is at a medium to light weight, aft center-of-gravity position, with symmetric fuel loading.
4.10.2.3 In the configurations listed below, trim the airplane at 1.3 VSR. Reduce speed approximately 1 knot per second using elevator control to 1 second past stall warning and demonstrate prompt recovery to the trim speed using elevator control.
4.10.2.3.1 High lift devices retracted configuration, maximum continuous power or thrust.
4.10.2.3.2 Maximum lift landing configuration, maximum continuous power or thrust.
4.11 Directional and Lateral Control, § 25.147.
To show compliance with § 25.147, applicants should combine qualitative evaluations with the other testing (for example, the roll tests described in paragraphs 4.9.2.3.1 and
4.9.2.4 of this AC). Review the results of the tests on the uncontaminated airplane for any cases of marginal compliance. All tests showing marginal compliance should be repeated with ice accretions on the airplane.
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4.12 Trim, § 25.161.
4.12.1 To show compliance with this requirement, the applicant should combine qualitative evaluations with the other testing. Review results of tests on the uncontaminated airplane for any cases of marginal compliance. All tests showing marginal compliance should be repeated with ice accretions on the airplane. In addition, a specific check should be made to demonstrate compliance with § 25.161(c)(2).
4.12.2 Acceptable Test Program.
The following specifications represent an example of an acceptable test program for compliance with § 25.161(c)(2).
Maneuvers
4.12.2.1 The holding ice accretion should be used.
4.12.2.2 The airplane is at the most critical landing weight, with a forward center of gravity position and symmetric fuel loading.
4.12.2.3 In the maximum lift landing configuration, trim the airplane at the most critical of—
4.12.2.3.1 1.3 VSR1 at idle power or thrust, or
4.12.2.3.2 VREF with the power or thrust for a -3° flight path angle.
4.13 Stability—General, § 25.171.
To show compliance with this requirement, applicants should combine qualitative evaluations with the other testing. Each tendency to change speed when trimmed and a need for frequent trim inputs should be specifically investigated.
4.14 Demonstration of Static Longitudinal Stability, § 25.175.
4.14.1 To show compliance with § 25.175, the applicant should test each of the following cases. In general, it is not necessary to test in the cruise configuration at low speed (§ 25.175(b)(2)) or in the cruise configuration with landing gear extended (§ 25.175(b)(3)); nor is it necessary to test at high altitude. Maximum speed for substantiation of stability characteristics in icing conditions (as prescribed by § 25.253(c)) is the lowest of—
• 300 knots calibrated airspeed (CAS),
• VFC, or
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• A speed at which it is demonstrated that the airframe will be free of ice accretion due to the effects of increased dynamic pressure.
4.14.2 Acceptable Test Program.
The following specifications represent an example of an acceptable test program for demonstrating static longitudinal stability.
Maneuvers
4.14.2.1 The holding ice accretion should be used.
4.14.2.2 The airplane is at a high landing weight, aft center-of-gravity position, with symmetric fuel loading.
4.14.2.3 In the configurations listed in paragraphs 4.14.2.3.1 through 4.14.2.3.4 below, trim the airplane at the specified speed. The power or thrust should be set and stability demonstrated over the speed ranges as stated in § 25.175(a) through (d), as applicable.
4.14.2.3.1 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.
4.14.2.3.2 Cruise: With high lift devices retracted, trim at VMO or 250 knots CAS, whichever is lower.
4.14.2.3.3 Approach: With the high lift devices in the approach position appropriate to the highest lift landing configuration, trim at 1.3 VSR.
4.14.2.3.4 Landing: With the highest lift landing configuration, trim at 1.3 VSR.
4.15 Static Lateral–Directional Stability, § 25.177.
4.15.1 Use steady heading sideslips to show compliance with the directional and lateral stability requirements. The maximum sideslip angles obtained should be recorded and may be used to substantiate a crosswind value for landing. (See paragraph 4.19 of this AC.) Section 25.177(c) requires directional and lateral control movements and forces to be substantially proportional to the angle of sideslip without reversing.
4.15.2 Acceptable Test Program.
The following specifications represent an example of an acceptable test program for demonstrating static directional and lateral stability.
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Maneuvers
4.15.2.1 The holding ice accretion should be used.
4.15.2.2 The airplane is at a medium to light weight, aft center-of-gravity position, with symmetric fuel loading.
4.15.2.3 In the configurations listed below, trim the airplane at the specified speed and conduct steady heading sideslips to full rudder authority, 180 pounds of rudder pedal force, or full lateral control authority, whichever comes first:
4.15.2.3.1 High lift devices retracted configuration: Trim at best rate-of-climb speed, but need not be less than 1.3 VSR.
4.15.2.3.2 Lowest lift takeoff configuration: Trim at the all-engines-operating initial climb speed.
4.15.2.3.3 Highest lift landing configuration: Trim at VREF.
4.16 Dynamic Stability, § 25.181.
If the uncontaminated airplane has no borderline compliance test results for § 25.181, dynamic stability tests with ice accretions on the airplane are not necessary. The applicant should combine qualitative evaluations with other testing. Each difficulty in achieving precise attitude control and each tendency to sustain oscillations in turbulence should be investigated.
4.17 Stall Demonstration, § 25.201/Stall Characteristics, § 25.203.
4.17.1 The applicant should conduct sufficient stall testing to demonstrate that the stall characteristics comply with the requirements of §§ 25.201 and 25.203. In general, it is not necessary to conduct a stall program that encompasses all weights, center-of-gravity positions, altitudes, high lift configurations, deceleration device configurations, straight and turning flight attitudes, and thrust or power settings. The applicant can establish a reduced test matrix based on a review of the stall characteristics of the uncontaminated airplane. However, additional tests may be necessary if—
4.17.1.1 The stall characteristics with ice accretion show a significant difference from those on the uncontaminated airplane,
4.17.1.2 The testing indicates borderline compliance, or
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4.17.1.3 The activation point of a stall identification system (for example, a stick pusher) is reset for icing conditions.
4.17.2 Acceptable Test Program.
Turning flight stalls at decelerations greater than 1 knot per second are not required.
Note that slow decelerations (much slower than 1 knot per second) may be critical on airplanes with anticipation logic in their stall protection system or on airplanes with low directional stability, where large sideslip angles could develop. The following specifications represent an example of an acceptable test program subject to the provisions outlined above.
Maneuvers
4.17.2.1 The holding ice accretion should be used.
4.17.2.2 The airplane should be loaded to a medium to light weight, aft center-of-gravity position, with symmetric fuel loading.
4.17.2.3 The tests should be conducted at the normal stall test altitude.
4.17.2.4 In the configurations listed in paragraphs 4.17.2.4.1 through 4.17.2.4.4 below, trim the airplane at the same initial stall speed factor used for stall speed determination. For power on stalls, use the power setting as defined in § 25.201(a)(2), but with ice accretions on the airplane. Decrease speed at a rate not to exceed 1 knot per second to stall identification and recover using the same recovery maneuver as for the uncontaminated airplane.
4.17.2.4.1 High lift devices retracted configuration: Straight/Power Off, Straight/Power On, Turning/Power Off, Turning/Power On.
4.17.2.4.2 Lowest lift takeoff configuration: Straight/Power On, Turning/Power Off.
4.17.2.4.3 Highest lift takeoff configuration: Straight/Power Off, Turning/Power On.
4.17.2.4.4 Highest lift landing configuration: Straight/Power Off, Straight/Power On, Turning/Power Off, Turning/Power On.
4.17.2.5 For the configurations listed in paragraphs 4.17.2.4.1 and 4.17.2.4.4 above, and each other configuration if deemed more critical, in 1 knot per second deceleration rates down to stall warning with wings level and power off, roll the airplane left and right up to 10° of bank using the lateral control.