AC 25-7D

AC 25-7D CHG 1

§ 25.121(d), as limited by the applicable controllability requirements. It must be possible, without requiring exceptional piloting skill, to prevent losing altitude during the maneuver. Trimming is permissible at any time during the maneuver. If gates are provided, conduct this test beginning from the maximum landing flap position to the first gate, from gate to gate, and from the last gate to the fully retracted position. If there is a gate between any landing position and its associated go-around position(s), this test should also be conducted from that landing position through the gate to the associated go-around position. If there is more than one associated go-around position, this additional test should be conducted using the goaround position corresponding to the most retracted flap position, unless another position is more critical. Keep the landing gear extended throughout the test.

5.2.2.7 Longitudinal Control, Out-of-Trim Takeoff Conditions— §§ 25.107(e)(4) and 25.143(a)(1).

See paragraphs 4.2.9.3.3 and 4.2.9.3.4 of this AC.

5.3 Directional and Lateral Control—§ 25.147.

5.3.1 Explanation.

5.3.1.1 Sections 25.147(a) and (b) provide criteria to determine if the airplane may have dangerous characteristics such as rudder lock or loss of directional control if it is maneuvered only with the rudder, while maintaining wings level, when one or two critical engines are inoperative.

Some yaw capability into the operating engine(s) should be possible. It should also be possible to make reasonably sudden heading changes of up to 15°, as limited by rudder force or deflection, toward the inoperative engine(s). The intention of the requirement is that the airplane can be yawed as prescribed without needing to bank the airplane. Small variations of bank angle that are inevitable in a realistic flight test demonstration are acceptable.

5.3.1.2 Sections 25.147(c) and (e) require an airplane to be easily controllable with the critical engine(s) inoperative. Section 25.147(d) further requires that lateral control be sufficient to provide a roll rate necessary for safety, without excessive control forces or travel, at the speeds likely to be used with one engine inoperative. Compliance can normally be demonstrated in the takeoff configuration at V2 speed, because this condition is usually the most critical. Normal operation of a yaw stability augmentation system (SAS) should be considered in accordance with the normal operating procedures. Roll response with all engines operating, § 25.147(f), should be satisfactory for takeoff, approach, landing, and high-speed configurations. Any permissible configuration that could affect roll response should be evaluated.

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5.3.2 Procedures.

The following test procedures outline an acceptable means for demonstrating compliance with § 25.147.

5.3.2.1 Directional Control: General—§ 25.147(a).

5.3.2.1.1 Configuration.

 Maximum landing weight.

 Most aft CG position.

 Wing flaps extended to the approach position.

 Landing gear retracted.

 Yaw SAS on, and off if applicable.

 Operating engine(s) at the power or thrust for level flight at 1.3 VSR, but not more than maximum continuous power or thrust.

 Inoperative engine that would be most critical for controllability, with the propeller (for propeller airplanes) feathered.

5.3.2.1.2 Test Procedure.

The airplane must be trimmed in level flight at the most critical altitude in accordance with § 25.21(c). Make heading changes into and away from the inoperative engine of up to 15° (not using more than 150 lbs rudder force), using the roll controls to maintain approximately wings level flight.

The airplane should be controllable and free from any hazardous characteristics during this maneuver. For airplanes equipped with a rudder boost system, the evaluation should be done without rudder boost if the boost system can be inoperative.

5.3.2.2 Directional Control: Four or More Engines—§ 25.147(b).

5.3.2.2.1 Configuration.

 Maximum landing weight.

 Most forward CG position.

 Wing flaps in the most favorable climb position (normally retracted).

 Landing gear retracted.

 Yaw SAS on, and off, as applicable.

 Operating engines at the power or thrust required for level flight at

1.3 VSR1, but not more than maximum continuous power or thrust.

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 Two inoperative engines that would be most critical for controllability with (if applicable) propellers feathered.

5.3.2.2.2 Test Procedure.

The procedure outlined in paragraph 5.3.2.1.2 above is applicable to this test.

5.3.2.3 Lateral Control: General—§ 25.147(c).

5.3.2.3.1 Configuration.

 Maximum takeoff weight.

 Most aft CG position.

 Wing flaps in the most favorable climb position.

 Landing gear retracted and extended.

 Yaw SAS on, and off, as applicable.

 Operating engine(s) at maximum continuous power or thrust.

 The inoperative engine that would be most critical for controllability, with the propeller (for propeller airplanes) feathered.

5.3.2.3.2 Test Procedure.

With the airplane trimmed at 1.3 VSR1, turns with a bank angle of 20° must be demonstrated with and against the inoperative engine from a steady climb at 1.3 VSR1. It should not take exceptional piloting skill to make smooth, predictable turns.

5.3.2.4 Lateral Control: Roll Capability—§ 25.147(d).

5.3.2.4.1 Configuration.

 Maximum takeoff weight.

 Most aft CG position.

 Wing flaps in the most critical takeoff position.

 Landing gear retracted.

 Yaw SAS on, and off, as applicable.

 Operating engine(s) at maximum takeoff power or thrust.

 The inoperative engine that would be most critical for controllability, with propellers (for propeller airplanes) feathered.

5.3.2.4.2 Test Procedure.

With the airplane in trim, or as nearly as possible in trim, for straight flight at V2, establish a steady 30° banked turn. Demonstrate that the airplane 5-22

can be rolled to a 30° bank angle in the other direction in not more than 11 seconds. The rudder may be used to the extent necessary to minimize sideslip. Demonstrate this maneuver in the most adverse direction. The maneuver may be unchecked, that is, the pilot need not apply a control input to stop the roll until after the 30° bank angle is achieved. Care should be taken to prevent excessive sideslip and bank angle during the recovery.

5.3.2.5 Lateral Control: Four or More Engines—§ 25.147(e).

5.3.2.5.1 Configuration.

 Maximum takeoff weight.

 Most aft CG position.

 Wing flaps in the most favorable climb position.

 Landing gear retracted and extended.

 Yaw SAS on, and off, as applicable.

 Operating engines at maximum continuous power or thrust.

 Two inoperative engines most critical for controllability, with propellers (for propeller airplanes) feathered.

5.3.2.5.2 Test Procedure.

The procedure outlined in paragraph 5.3.2.1.2 is applicable to this test.

5.3.2.6 Lateral Control: All Engines Operating—§ 25.147(f).

5.3.2.6.1 Configuration.

All configurations within the flight envelope for normal operation.

5.3.2.6.2 Test Procedure.

This is primarily a qualitative evaluation that should be conducted throughout the test program. Roll performance should be investigated throughout the flight envelope, including speeds to VFC/MFC, to ensure adequate peak roll rates for safety, considering the flight condition, without excessive control force or travel. Roll response during sideslips expected in service should provide maneuvering capabilities adequate to recover from such conditions. Approach and landing configurations should be carefully evaluated to ensure adequate control to compensate for gusts and wake turbulence while in close proximity to the ground.

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5.4 Minimum Control Speed—§ 25.149.

5.4.1 Explanation.

5.4.1.1 General.

Section 25.149 defines requirements for minimum control speeds during takeoff climb (VMC), during takeoff ground roll (VMCG), and during approach and landing (VMCL and VMCL-2). The VMC (commonly referred to as VMCA) requirements are specified in § 25.149(a), (b), (c) and (d); the VMCG requirements are described in § 25.149(e); and the VMCL and VMCL-2 requirements are covered in § 25.149(f), (g) and (h). Section 25.149(a) states, “...the method used to simulate critical engine failure must represent the most critical mode of powerplant failure with respect to controllability expected in service.” That is, the power or thrust loss from the inoperative engine must be at the rate that would occur if an engine suddenly became inoperative in service. Prior to amendment 25-42 to § 25.149, the regulation required that rudder control forces must not exceed 180 lbs. With the adoption of amendment 25-42, rudder control forces became limited to 150 lbs. The relationships between VEF, V1, and VMCG are discussed in paragraph 4.2, Takeoff and Takeoff Speeds— §§ 25.105 and 25.107, and paragraph 4.3, Accelerate-Stop Distance— § 25.109.

5.4.1.2 Safety Concerns Addressed by VMCA.

When flying with an inoperative engine, the asymmetric yawing moment must be compensated by aerodynamic forces created by rudder deflection and sideslip. When the speed decreases, sideslip increases rapidly in a non-linear manner. The purpose of the VMCA requirement is to ensure the airplane remains safely controllable with the maximum power or thrust asymmetry at any speed down to VMCA.

5.4.1.3 Weight Effect on VMCA.

To maintain straight flight with an inoperative engine, as required by § 25.149(b), the lateral aerodynamic forces resulting from sideslip and rudder deflection must be balanced by the lateral component of weight

(i.e., W * sin (bank angle)). The bank angle necessary to maintain straight flight is therefore approximately inversely proportional to the weight.

Since § 25.149(b) allows VMCA to be determined with up to 5° of bank angle, this introduces a weight effect on VMCA. The heavier the weight, the lower the VMCA, but the greater will be the demonstrated sideslip. As an example, flying a heavy airplane at a VMCA speed determined at a lighter weight will result in the same sideslip, but a smaller bank angle (e.g., 4° instead of 5° if the airplane is 25 percent heavier).

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5.4.2 Procedures: General.

5.4.2.1 Prior to beginning the minimum control speed tests, the applicant should verify which engine’s failure will result in the largest asymmetric yawing moment (i.e., the “critical” engine). This is typically done by setting one outboard engine to maximum power or thrust, setting the corresponding opposite engine at idle, and decelerating with wings level until full rudder is required. By alternating power or thrust on/power or thrust off from left to right, the critical engine can be defined as the idle engine that requires the highest minimum speed to maintain a constant heading with full rudder deflection.

5.4.2.2 For propeller-driven airplanes, VMCA, VMCG, and VMCL (and VMCL-2, as applicable) should be determined by rendering the critical engine(s) inoperative and allowing the propeller to attain the position it automatically assumes. However, for some engine/propeller installations, a more critical drag condition could be produced as the result of a failure mode that results in a partial power condition that does not activate the automatic propeller drag reduction system (e.g., autofeather system). One example is a turbopropeller installation that can have a fuel control failure, which causes the engine to go to flight idle, resulting in a higher asymmetric yawing moment than would result from an inoperative engine.

In such cases, in accordance with § 25.149(a), the minimum control speed tests must be conducted using the most critical failure mode. For propeller-driven airplanes where VMCA is based on operation of a propeller drag reduction system, VMCA should also be defined with the critical engine at idle to address the training situation where engine failure is simulated by retarding the critical engine to idle. If VMCA at idle is more than one knot greater than for the engine failure with an operating drag reduction system, the idle engine VMCA should be included in the normal procedures section of the AFM as advisory information to maintain the level of safety in the aforementioned training situation.

5.4.2.3 AFM values of VMCA, VMCG, and VMCL (and VMCL-2, as applicable) should be based on the maximum net power or thrust reasonably expected for a production engine. These speeds should not be based on specification power or thrust, since this value represents the minimum power or thrust guaranteed by the engine manufacturer, and the resulting minimum control speeds will not be representative of what could be achieved in operation.

The maximum power or thrust used for scheduled AFM minimum control speeds should represent the high side of the tolerance band but may be determined by analysis instead of tests.

5.4.2.4 When determining VMCA, VMCL and VMCL-2, consideration should be given to the adverse effect of maximum approved lateral fuel imbalance on lateral control availability. This is especially of concern if tests or analysis 5-25

show that the lateral control available is the determining factor of a particular VMC.

5.4.2.5 For changes to approved designs, the effect of any aerodynamic or propulsive changes on compliance with 25.149 must be assessed per § 21.20. For example, for design changes involving an increase in engine thrust, the effect of the higher thrust on minimum control speeds must be specifically evaluated, and, if found to be not negligible, must be accounted for.

5.4.3 Procedures: Minimum Control Speeds—Air (VMCA).

5.4.3.1 In showing compliance with the VMCA requirements, the following two conditions should be satisfied:

5.4.3.1.1 The stabilized (static) condition where constant heading is maintained without exceeding a 5° bank angle, and

5.4.3.1.2 The dynamic condition in which control is maintained without exceeding a heading change of 20°.

Note: Separate tests are usually conducted to show compliance with these two conditions.

5.4.3.2 Static Test Procedure and Required Data.

5.4.3.2.1 To determine VMCA, use the configuration specified in § 25.149, except that VMCA is normally determined at minimum weight in order to minimize the stall speed and because static VMCA decreases with increased weight if a 5° bank angle is used. The requirement of § 25.149(c) that VMCA not exceed 1.13 VSR is based on VSR at maximum sea level takeoff weight. With the critical engine inoperative, the corresponding opposite engine should be adjusted to maximum takeoff power/thrust, and the airspeed decreased until heading can just be maintained with full rudder and no more than a 5° bank into the operating engine. For airplanes with more than two engines, the inboard engine(s) may be set to any power or thrust necessary to assist in developing the desired level of asymmetric power or thrust, or to achieve the desired flight path angle (normally level flight).

5.4.3.2.2 If the maximum asymmetric power or thrust that is permitted by the AFM operating limitations was maintained at the test day VMCA, and the rudder pedal force did not exceed the limit specified in § 25.149(d), the resulting speed may be used as the single value of VMCA for the airplane. If, at the option of the applicant, the AFM value of VMCA is to vary with pressure altitude and temperature, the test day minimum control speed and the corresponding power or thrust should be used to calculate an equivalent yawing moment coefficient (CN). This CN value may then be used to 5-26

calculate VMCA as a function of takeoff power or thrust, thus permitting VMCA to be scheduled as a function of pressure altitude and temperature for takeoff data expansion and presentation in the AFM. (See appendix F of this AC for further discussion of VMCA correction.)

5.4.3.2.3 If maximum allowable takeoff power or thrust could not be developed at the flight test conditions, but maximum rudder deflection was achieved, then the VMCA value corresponding to sea level standard day maximum asymmetric power or thrust may be calculated from the CN attained at the test value of VMCA. Extrapolation using this constant CN method should be limited to 5 percent of the test day asymmetric power or thrust and should only be permitted if the rudder pedal force at the test day VMCA was not more than 95 percent of the limit value specified in § 25.149(d). For extrapolation beyond 5 percent power or thrust, a more rigorous analysis, using all the applicable stability and control terms, should be made. (See appendix F of this AC for further discussion of VMCA correction.)

5.4.3.2.4 If VMCA could not be achieved due to stall buffet, or excessive rudder pedal force, a parametric investigation should be undertaken to determine whether VMCA is limited by stall speed, maximum rudder deflection, or maximum allowable rudder pedal force. (See appendix G of this AC.)

5.4.3.3 Dynamic Test Procedures and Required Data.

5.4.3.3.1 After the static VMCA tests have been completed, dynamic engine cuts should be evaluated at a series of decreasing airspeeds to show that sudden engine failure at any speed down to the static VMCA value meets the requirements of § 25.149. The dynamic VMCA test is conducted by applying the maximum approved power/thrust to all outboard engines, stabilizing at the test airspeed, and then cutting fuel to the critical engine.

The pilot must be able to recover to a straight flight condition (constant heading) with an angle of bank of not more than 5°.

 Without deviating more than 20 degrees from the original heading,  While maintaining the test airspeed, without reducing power/thrust on the operating engine(s), and  Without exceeding the rudder pedal force limit of § 25.149(d).

5.4.3.3.2 In accordance with § 25.149(d), the airplane may not assume any dangerous attitude, nor require exceptional piloting skill, alertness, or strength. The maximum bank angle achieved during the tests may exceed 5° provided the airplane characteristics comply with this qualitative requirement. If the dynamic tests result in a VMCA greater than the static value, the increment between the static and dynamic VMCA at the same altitude should be added to the sea level extrapolated value. If the dynamic value is less than the static value, the static VMCA should be used for the AFM data expansion.

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5.4.3.3.3 If static VMCA is near stall speed at the minimum practicable test weight, or if the thrust-to-weight ratio (T/W) results in a trimmed pitch attitude of more than 20°, it is not feasible to attempt to accurately define a quantitative value of VMCA using a sudden engine cut because of the dynamics of the rapid pitch down maneuver required, and the hazard associated with a potential spin entry. Additionally, an extreme nose up attitude followed by an engine cut is not representative of an operational takeoff engine failure. Since § 25.107(e)(1)(ii) requires VR to be not less than 1.05 VMCA, and there is some additional speed increase prior to lift off, a transport airplane is typically never airborne below approximately

1.08 VMCA. Therefore, instead of using the dynamic method to define VMCA for these aircraft with high T/W or stall speed coincident with VMCA, it is more appropriate for a dynamic engine cut to be evaluated only for acceptable controllability, and at a more representative speed. For these airplanes, a dynamic engine cut should be evaluated at an airspeed of either 1.08 VSR or 1.1 VMCA (static), whichever is greater. During the entry to, and recovery from this maneuver, all the requirements of § 25.149(d) must be met.

5.4.3.3.4 For airplanes with rudder travel-limited VMCA that have increased power or thrust engines installed, with no changes to the airframe’s geometric layout or dimensions, it may not be necessary to conduct dynamic VMCA flight testing if the power or thrust has not increased more than 10 percent above the level at which dynamic VMCA had previously been demonstrated. (See appendix F of this AC.)

5.4.4 Procedures: Minimum Control Speed-Ground (VMCG)—§ 25.149(e).

5.4.4.1 It must be demonstrated that, when the critical engine is suddenly made inoperative at VMCG during the takeoff ground roll, the airplane is safely controllable if the takeoff is continued. During the demonstration, the airplane must not deviate more than 30 feet (25 feet prior to amendment 25-42) from the pre-engine-cut projected ground track. The critical engine) for ground minimum control speed testing should be determined during the takeoff ground run using techniques similar to these described in paragraph 5.4.2. If there is a significant difference in left and right rudder deflection, the loss of asymmetric propeller disc loading, due to near zero angle-of-attack during the takeoff roll, could result in the critical engine being on the opposite side of the airplane relative to the airborne minimum control speed tests.

5.4.4.2 Work up tests may be conducted by abruptly retarding the critical engine to idle to determine the airplane asymmetric control characteristics and provide data from which an estimate of VMCG can be made. Due to the engine spindown characteristics with the critical engine retarded to idle, the speed will not, in general, be representative of the VMCG speed that would be obtained with a fuel cut. Therefore, the certification tests for 5-28

VMCG should be conducted using fuel cuts. Starting from a speed comfortably above the estimated VMCG and with the maximum takeoff power or thrust level to be certified, several fuel cuts should be made at decreasing calibrated airspeeds to establish the minimum airspeed at which the lateral deviation is less than or equal to 30 feet. VMCG is determined for zero crosswind conditions. However, in light crosswind test conditions the VMCG value determined should be that which is appropriate to the adverse crosswind or, at the applicant’s option, may be corrected to a zero crosswind value using runs made on reciprocal headings.

5.4.4.3 During determination of VMCG, engine failure recognition should be provided by the pilot:

 Feeling a distinct change in the directional tracking characteristics of the airplane, or  Seeing a directional divergence of the airplane with respect to the view outside the airplane.

5.4.4.4 Directional control of the airplane should be accomplished by use of the rudder only. All other controls, such as ailerons and spoilers, should only be used to correct any alterations in the airplane attitude and to maintain a wings level condition. Pilot input to controls to supplement the rudder effectiveness should not be used. Care should also be taken not to inadvertently apply brake pressure during large rudder deflections, as this will invalidate the test data.

5.4.4.5 VMCG testing should be conducted at the most critical weight in the range where VMCG may impact AFM V1 speeds.

5.4.4.6 VMCG testing should be conducted at aft CG and with the nose wheel free to caster, to minimize the stabilizing effect of the nose gear. If the nose wheel does not caster freely, the test may be conducted with enough nose up elevator applied to lift the nose wheel off the runway.

5.4.4.7 VMCG testing should not be conducted on runways with excessive crowning (i.e., cross-runway slope) unless the effects of such crowning are determined to be conservative.

5.4.4.8 For airplanes with certification bases prior to amendment 25-42, VMCG values may be demonstrated with nose wheel rudder pedal steering operative for dispatch on wet runways. The test should be conducted on an actual wet, smooth (i.e., not grooved or PFC) runway. The test(s) should include engine failure at or near a minimum VEF associated with minimum VR to demonstrate adequate controllability during rotation, liftoff, and the initial climbout. The VMCG values obtained by this method are applicable for wet or dry runways only, not for icy runways.

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5.4.5 Procedures: Minimum Control Speed during Approach and Landing (VMCL)— § 25.149(f).

5.4.5.1 This section is intended to ensure that the airplane is safely controllable following an engine failure during an all-engines-operating approach and landing. From a controllability standpoint, the most critical case usually consists of an engine failing after the power or thrust has been increased to perform a go-around from an all-engines-operating approach.

Section 25.149(f) requires the minimum control speed to be determined that allows a pilot of average skill and strength to retain control of the airplane after the critical engine becomes inoperative and to maintain straight flight with less than 5° of bank angle. Section 25.149(h) requires that sufficient lateral control be available at VMCL to roll the airplane through an angle of 20°, in the direction necessary to initiate a turn away from the inoperative engine, in not more than five seconds when starting from a steady straight flight condition.

5.4.5.2 Conduct this test using the most critical of the all-engines-operating approach and landing configurations or, at the option of the applicant, each of the all-engines-operating approach and landing configurations.

The procedures given in paragraphs 5.4.3.2 and 5.4.3.2.3 for VMCA may be used to determine VMCL, except that flap and trim settings should be appropriate to the approach and landing configurations, the power or thrust on the operating engine(s) should be set to the go-around power or thrust setting, and compliance with all VMCL requirements of § 25.149(f) and (h) must be demonstrated.

5.4.5.3 In accordance with § 25.149(f)(5) for propeller driven airplanes, the propeller must be in the position it achieves without pilot action following engine failure, assuming the engine fails while at the power or thrust necessary to maintain a 3° approach path angle.

5.4.5.4 At the option of the applicant, a one-engine-inoperative landing minimum control speed, VMCL(1 out), may be determined in the conditions appropriate to an approach and landing with one engine having failed before the start of the approach. In this case, only those configurations recommended for use during an approach and landing with one engine inoperative need be considered. The propeller of the inoperative engine, if applicable, may be feathered throughout. The resulting value of VMCL(1 out) may be used in determining the recommended procedures and speeds for a one-engine-inoperative approach and landing.

5.4.6 Procedures: Minimum Control Speed with Two Inoperative Engines during Approach and Landing (VMCL-2)—§ 25.149(g).

5.4.6.1 For airplanes with three or more engines, VMCL-2 is the minimum speed for maintaining safe control during the power or thrust changes that are likely 5-30

to be made following the failure of a second critical engine during an approach initiated with one engine inoperative.

5.4.6.2 In accordance with § 25.149(g)(5) for propeller driven airplanes, the propeller of the engine that is inoperative at the beginning of the approach may be in the feathered position. The propeller of the more critical engine must be in the position it automatically assumes following engine failure.

5.4.6.3 Conduct this test using the most critical approved one-engine-inoperative approach or landing configuration (usually the minimum flap deflection), or at the option of the applicant, each of the approved one-engine-inoperative approach and landing configurations. The following demonstrations should be conducted to determine VMCL-2:

5.4.6.3.1 With the power or thrust on the operating engines set to maintain a -3° glideslope with one critical engine inoperative, the second critical engine is made inoperative, and the remaining operating engine(s) are advanced to the go-around power or thrust setting. The VMCL-2 speed is established by the procedures presented in paragraphs 5.4.3.2 and 5.4.3.3 below for VMCA, except that flap and trim settings should be appropriate to the approach and landing configurations, the power or thrust on the operating engine(s) should be set to the go-around power or thrust setting, and compliance with all VMCL-2 requirements of § 25.149(g) and (h) must be demonstrated.

5.4.6.3.2 With power or thrust on the operating engines set to maintain a -3° glideslope, with one critical engine inoperative:

1. Set the airspeed at the value determined in paragraph 5.4.6.3.1 above and, with zero bank angle, maintain a constant heading using trim to reduce the control force to zero. If full trim is insufficient to reduce the control force to zero, full trim should be used plus control deflection as required; and

2. Make the second critical engine inoperative and retard the remaining operating engine(s) to minimum available power or thrust without changing the directional trim. The VMCL-2 determined in paragraph 5.4.6.3.1 is acceptable if constant heading can be maintained without exceeding a 5° bank angle and the limiting conditions of § 25.149(h).

3. Starting from a steady straight flight condition, demonstrate that sufficient lateral control is available at VMCL-2 to roll the airplane through an angle of 20° in the direction necessary to initiate a turn away from the inoperative engines in not more than five seconds. This maneuver may be flown in a bank-to-bank roll through a wings level attitude.

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