AC 25-7D CHG 1
operation, such as maintaining adequate margin to the in-ground-effect stall angle-of-attack during a dynamic takeoff maneuver, V2 may be forced to be greater than V2MIN for some, if not all, of the thrust/weight range of operation. In addition, § 25.111(c)(2) stipulates that the airplane must reach V2 before it is 35 feet above the takeoff surface and continue at a speed not less than V2 until it is 400 feet above the takeoff surface.
These requirements were first expressed in Special Civil Air Regulation No. SR-422, Turbine-Powered Transport Category Airplanes of Current Design (SR-422A), paragraphs 4T.114(b)(4) and (c)(3) and 4T.116(e).
The concern that the regulation change was addressing was the overshoot of V2 after liftoff under the previous requirement that the airplane attain V2 on, or near, the ground. The intent of the current requirement is to allow an acceleration to V2 after liftoff but not to allow a decrease in the field length required to attain a height of 35 feet above the takeoff surface by attaining a speed greater than V2, under low drag ground conditions, and using the excess kinetic energy to attain the 35-foot height.
4.2.7.2 In the case of turbojet powered airplanes, when most of the one-engine-inoperative data have been collected using throttle chops, V2, and its relationship to VR, should be substantiated by at least a limited number of fuel cuts at VEF. For derivative programs not involving a modification that would affect thrust decay characteristics, demonstrations of fuel cuts may be unnecessary.
4.2.7.3 For propeller-driven airplanes, the use of fuel cuts can be more important to ensure that the takeoff speeds and distances are obtained with the critical engine’s propeller attaining the position it would during a sudden engine failure. The number of tests that should be conducted using fuel cuts depends on the correlation obtained with the throttle chop data and substantiation that the data analysis methodology adequately models the effects of a sudden engine failure.
4.2.8 Procedures: Section 25.107(d)—Minimum Unstick Speed (VMU).
4.2.8.1 Section 25.107(d) states, “VMU speeds must be selected by the applicant.”
An applicant can either determine the lowest possible VMU speeds or select a higher speed that supports the takeoff performance targets of the airplane. Regardless of how the applicant selects the VMU speeds, compliance must be shown with § 25.107(d), (e)(1)(iv), (e)(3), and (e)(4) to show that the selected VMU speeds allow the airplane to safely lift off the ground and continue the takeoff.
4.2.8.2 An applicant should comply with § 25.107(d) by conducting VMU tests with all engines operating and also with one engine inoperative. During these tests, the takeoff should be continued until the airplane is out of 4-8
AC 25-7D CHG 1 ground effect. The airplane pitch attitude should not be decreased after liftoff.
4.2.8.3 VMU testing to demonstrate the lowest VMU speed is a maximum performance flight test maneuver, and liftoff may occur very near the angle-of-attack for maximum lift coefficient in ground effect, with the minimum margin to in-ground-effect stall occurring in the vicinity of liftoff. As discussed in paragraph 4.2.2 of this AC, to ensure flight test safety, a thorough understanding of the stall angle-of-attack in ground effect and appropriate angle-of-attack margins should be established and maintained during testing (see Figure 4-A). In addition, even though pitch attitude may be held fairly constant during the maneuver, environmental conditions and transiting through ground effect may result in changes in angle-of-attack. It is permissible to lift off at a speed that is below the normal stall warning speed, provided no more than light buffet is encountered. The use of a flight test device that restricts the on-ground pitch attitude has been found useful by some manufacturers in reducing the risk of over-rotation and in-ground-effect stall.
4.2.8.3.1 It is important for the flight test team to understand the control laws and any transitions between control laws during takeoff (e.g., based on weight on wheels) for an electronic flight control system that may present unique hazards that should be taken into account.
4.2.8.3.2 An artificial stall warning system (e.g., a stick shaker) may be disabled or adjusted to a more suitable value during VMU testing.
4.2.8.3.3 If the airplane is equipped with a stick pusher, high angle-of-attack limiting function, or other system that may affect the conduct of the test, the angle of attack setting for activation of the system may be selected by the applicant and differ from the nominal setting. The system may alternatively be disabled or its activation delayed for test purposes until a safe altitude is reached. However, for airplanes equipped with a stick pusher that is not designed to be inhibited during takeoff, the VMU test demonstrations will need to be assessed and will only remain valid if the stick pusher would not have activated with the angle-of-attack indication means set at the lowest angle within production tolerances.
4.2.8.3.4 Note that if there are changes to an airplane’s aerodynamic stall angle due to ground effect, then a stall warning system, stick pusher, or high angleof-attack limiting function that is not specifically designed to account for ground effect may not activate prior to an aerodynamic stall, during a VMU test. The airplane’s stall angle-of-attack and angle-of-attack sensor corrections, both in and out of ground effect, must be thoroughly understood by the test crew to determine if these systems will provide the benefit of protecting the airplane during VMU testing.
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AC 25-7D CHG 1 Figure 4-A. In-Ground-Effect Stall Margin
4.2.8.4 In lieu of conducting one-engine-inoperative VMU tests, the applicant may conduct all-engines-operating VMU tests if all pertinent factors that would be associated with an actual one-engine-inoperative VMU test are simulated or otherwise taken into account. To take into account all pertinent factors, it may be necessary to adjust the resulting VMU test values analytically.
The factors to be accounted for should include at least the following:
Thrust/weight ratio for the one-engine-inoperative range.
Controllability (may be related to one-engine-inoperative free air tests, such as minimum control speed in the air (VMCA)).
Increased drag due to use of lateral/directional control systems.
Reduced lift due to use of devices such as wing spoilers for lateral control.
Adverse effects of use of any other systems or devices on control, drag, or lift.
4.2.8.5 The number of VMU tests needed may be minimized by testing only the critical all-engines-operating and one-engine-inoperative thrust/weight ratios, provided the VMU speeds determined at these critical conditions are used for the range of thrust/weights appropriate to the all-engines-operating and one-engine-inoperative configurations. The critical thrust/weight is established by correcting, to the VMU speed, the thrust that results in the airplane achieving its limiting one-engine-inoperative climb gradient at the normally scheduled speed and in the appropriate configuration.
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AC 25-7D CHG 1
4.2.8.6 Amendment 25-42, effective March 1, 1978, revised §§ 25.107(d) and
25.107(e)(1)(iv) in order to permit the one-engine-inoperative VMU to be determined by all-engines-operating tests at the thrust/weight ratio corresponding to the one-engine-inoperative condition. As revised, § 25.107(d) specifies that VMU must be selected for the range of thrust/weight ratios to be certificated, rather than for the all-enginesoperating and one-engine-inoperative conditions as was previously required. In determining the all-engines-operating thrust/weight ratio that corresponds to the one-engine-inoperative condition, consider trim and control drag differences between the two configurations in addition to the effect of the number of engines operating. The minimum thrust/weight ratio to be certificated is established by correcting, to the VMU speed, the thrust that results in the airplane achieving its limiting engine-out climb gradient in the appropriate configuration and at the normally scheduled speed.
4.2.8.7 To conduct the VMU tests, rotate the airplane as necessary to achieve the VMU attitude. It is acceptable to use some additional nose-up trim over the normal trim setting during VMU demonstrations. Even on airplanes that have sufficient control authority to achieve the target VMU attitude prior to liftoff, the use of additional nose-up trim can be beneficial to the conduct of the test by giving the pilot additional time to stabilize on the VMU attitude prior to lifting off. If additional nose-up trim is used, the additional considerations of paragraph 4.2.8.8 below apply. VMU is the speed at which the weight of the airplane is completely supported by aerodynamic lift and thrust forces. Some judgment may be necessary on airplanes that have tilting main landing gear bogies.
Determining the liftoff point from gear loads and wheel speeds has been found acceptable in past programs. After liftoff, the airplane should be flown out of ground effect. During liftoff and the subsequent climbout, the airplane should be fully controllable.
4.2.8.8 VMU Testing for Airplanes Having Limited Pitch Control Authority.
4.2.8.8.1 For some airplanes with limited pitch control authority, it may not be possible, at forward CG and normal trim, to rotate the airplane to a liftoff attitude where the airplane could otherwise perform a clean flyaway at a minimum speed had the required attitude been achieved. This may occur only over a portion of the takeoff weight range in some configurations.
Though generally associated with the inability of the pitch control surfaces to provide adequate pitching moment to rotate the airplane to the desired pitch attitude at low thrust/weight ratio conditions, the same phenomenon may occur at high thrust/weight ratio conditions for airplanes with high thrust lines (e.g., aft engines mounted high on the fuselage). When limited pitch control authority is clearly shown to be the case, VMU test conditions 4-11
AC 25-7D CHG 1 may be modified to allow testing aft of the forward CG limit and/or with use of more airplane nose-up trim than normal. The VMU data determined with this procedure should be corrected to those values representative of the appropriate forward limit; the variation of VMU with CG may be assumed to be like the variation of free air stalling speed with CG.
Although the development of scheduled takeoff speeds may proceed from these corrected VMU data, additional tests are required (see paragraph
4.2.8.8.2 below) to check that the relaxed VMU criteria have not neglected problems that might arise from operational variations in rotating airplanes with limited pitch control authority.
4.2.8.8.2 In the following assurance test, the airplane should demonstrate safe flyaway characteristics: Minimum speed liftoff should be demonstrated at the critical forward CG limit with normal trim. For airplanes with a cutback forward CG at heavy weight, two weight/CG conditions should be considered. The heavy weight tests should be conducted at maximum structural or maximum sea level climb-limited weight with the associated forward CG. The full forward CG tests should be conducted at the highest associated weight. Alternatively, testing may be conducted at a single weight if an analysis is provided that identifies the critical weight/CG combination with regard to limited pitch attitude capability for liftoff.
These assurance tests should be conducted at the thrust/weight ratio that is most critical for attaining a pitch attitude that will provide a minimum liftoff speed.
4.2.8.8.3 For airplanes that are limited by low thrust/weight conditions, tests should be conducted at the minimum thrust/weight ratio for both the simulated one-engine-inoperative test (i.e., symmetrical reduced thrust) case and the all-engines-operating case.
4.2.8.8.4 For airplanes that are limited by high thrust/weight conditions, tests should be conducted at the highest thrust/weight ratio within the airplane’s operating envelope for both the simulated one-engine-inoperative case
(i.e., symmetrical reduced thrust) and the all-engines-operating case.
4.2.8.8.5 One acceptable test technique is to hold full nose-up control column as the airplane accelerates. As pitch attitude is achieved to establish the minimum liftoff speed, pitch control may be adjusted to prevent over-rotation, but the liftoff attitude should be maintained as the airplane flies off the ground and out of ground effect.
4.2.8.8.6 The resulting liftoff speeds are acceptable if the test proves successful and the liftoff speed is at least 5 knots below the normally scheduled liftoff speed.
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AC 25-7D CHG 1
4.2.8.8.7 This minimum 5 knot margin from the scheduled liftoff speed provides some leeway for operational variations such as mistrim, CG errors, etc., that could further limit the elevator authority. The reduced VMU margins arising from this test, relative to those specified in § 25.107(e)(1)(iv), are considered acceptable because of the reduced probability of a pitch control authority-limited airplane getting into a high drag condition due to over-rotation.
4.2.8.9 VMU Testing for Geometry Limited Airplanes.
4.2.8.9.1 For airplanes that are geometry limited (i.e., the minimum possible VMU speeds are limited by tail contact with the runway), § 25.107(e)(1)(iv)(B) allows the VMU to VLOF speed margins to be reduced to 108 percent and 104 percent for the all-engines-operating and one-engine-inoperative conditions, respectively. The VMU demonstrated should be sound and repeatable. As discussed in paragraph 4.2.2 of this AC, to ensure flight test safety, a thorough understanding of the estimated stall angle-of-attack in ground effect and appropriate angle-of-attack margins should be established and maintained during testing.
4.2.8.9.2 An airplane that is deemed to be geometry limited at the conditions tested is expected to be geometry limited over its entire takeoff operating envelope. If this is not the case, the airplane is not considered geometry limited and the reduced VMU to VLOF speed margins do not apply. Also, if a flight-test device is used with the intent to artificially restrict the rotation attitude (typically more than 0.5 degrees below the production configuration) to prevent over-rotation, and the airplane would not otherwise be geometry limited, this airplane would not be considered geometry limited and the reduced VMU to VLOF speed margins do not apply.
4.2.8.9.3 One acceptable means for demonstrating compliance with §§ 25.107(d) and 25.107(e)(1)(iv) with respect to the capability for a safe liftoff and fly-away from the geometry limited condition is to show that at the lowest thrust-to-weight ratio for the all-engines-operating condition:
1. In the speed range from 96 to 100 percent of the actual liftoff speed, the aft under-surface of the airplane should be in contact with the runway. Because of the dynamic nature of the test, it is recognized that contact will probably not be maintained during this entire speed range, so some judgment is necessary. It has been found acceptable for contact to exist approximately 50 percent of the time that the airplane is in this speed range.
2. Beyond the point of liftoff to a height of 35 feet, the airplane’s pitch attitude should not decrease below that at the point of liftoff, nor should the speed increase more than 10 percent.
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AC 25-7D CHG 1
3. The horizontal distance from the start of the takeoff to a height of 35 feet above the takeoff surface should not be greater than 105 percent of the distance determined in accordance with § 25.113(a)(2) without applying the 115 percent factor.
4.2.8.10 VMU for a Stretched Version of a Tested Airplane.
4.2.8.10.1 VMU speeds obtained by flight testing one model of an airplane type may be used to generate VMU speeds for a geometry-limited stretched version of that airplane. If the short body airplane met the criteria for the 104/108 percent VMU/VLOF speed margin for geometry limited airplanes as permitted by § 25.107(e)(1)(iv)(B) and discussed in paragraph 4.2.8.9.1 above, then the flight tests described in paragraph 4.2.8.10.2 below should be performed on the stretched derivative. Otherwise, the flight tests described in paragraph 4.2.8.9.3 above should be performed on the stretched derivative.
4.2.8.10.2 Since the concern for tail strikes is increased with the stretched airplane, the following should be accomplished, in addition to normal takeoff tests, when the VMU schedule of the stretched derivative is derived from that of the shorter body parent airplane:
1. The VMU of the stretched derivative airplane should be determined by correcting the VMU of the shorter body tested airplane for the reduced runway pitch attitude capability and revised CG range of the stretched airplane. Alternatively, stretched airplane VMU speeds not determined in this manner should be substantiated by flight testing or a rational analysis. Scheduled rotation speeds for the stretched airplane should result in at least the required liftoff speed margins above the corrected VMU required by § 25.107(e)(1)(iv) for the one-engine-inoperative and all-engines-operating takeoff conditions.
2. At both the forward and aft CG limits, and over the thrust-to-weight range for each takeoff flap, the following takeoff tests should be accomplished. The tests described in paragraphs a and b below should be accomplished with not more than occasional, minor (i.e., non-damaging) tail strikes. As discussed in paragraph 4.2.2 of this AC, to ensure flight test safety, a thorough understanding of the estimated stall angle-of-attack in ground effect and appropriate angle-of-attack margins should be established and maintained during testing.
a. All-engines-operating, early rotation tests specified in paragraph 4.2.9.3.2, including both the rapid rotations and over-rotations as separate test conditions.
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AC 25-7D CHG 1
b. One-engine-inoperative, early rotation tests specified in paragraph 4.2.9.2 below.
c. All-engines-operating, moderate rotation rate (i.e., more rapid than normal) takeoff tests, using the scheduled VR and normal pitch attitude after liftoff. Tail strikes should not occur for this condition.
4.2.9 Procedures: Section 25.107(e)—Rotation Speed (VR).
4.2.9.1 VR in terms of calibrated airspeed, must be selected by the applicant. VR has a number of constraints that must be observed in order to comply with § 25.107(e):
4.2.9.1.1 VR may not be less than V1; however, it can be equal to V1 in some cases.
4.2.9.1.2 VR may not be less than 105 percent of VMCA.
4.2.9.1.3 VR must be a speed that will allow the airplane to reach V2 at or before reaching a height of 35 feet above the takeoff surface, when the takeoff is conducted using normal takeoff procedures.
4.2.9.1.4 VR must be a speed that will result in liftoff at a speed not less than 110 percent of VMU (unless geometry limited) for the all-engines-operating condition, and not less than 105 percent of the VMU (unless geometry limited) determined at the thrust/weight ratio corresponding to the one-engine-inoperative condition for each set of conditions, such as weight, altitude, temperature, and configuration when the airplane is rotated at its maximum practicable rate. For this requirement, maximum practicable rate depends on the airplane configuration, type of pitch controller, flight control system design, and the takeoff procedure.
The rotation rate need not be increased beyond the point that prevents capturing the normal takeoff rotation attitude, without using exceptional piloting skill or strength. Rotation rates between 120% and 150% of the nominal rate used in determination of the takeoff performance in accordance with §§ 25.105, 25.111, and 25.113 have previously been found acceptable. Alternatively, this rotation rate can be determined analytically as a representatively high rotation rate from a significant sampling of takeoffs performed during the flight test program, including the takeoff field-performance tests.
4.2.9.1.5 VR may not be less than the speed necessary to demonstrate the oneengine inoperative and all-engines-operating in-service variation tests (early rotation, over-rotation, out-of-trim) from the requirements of § 25.107(e)(3) and (4), which specify that expected variations in service should not result in any unsafe flight characteristics or a marked increase 4-15
AC 25-7D CHG 1 in takeoff distance. As discussed in paragraph 4.2.2 of this AC, to ensure flight test safety, a thorough understanding of the estimated stall angle-ofattack in ground effect and appropriate angle-of-attack margins should be established and maintained during testing. It should be noted that ensuring successful demonstrations for these in-service variation criteria may in some cases require increasing VR (and thus V2) to a higher speed than what would otherwise be required by § 25.107(e)(1).
4.2.9.2 Early Rotation, One-Engine-Inoperative Test.
4.2.9.2.1 In showing compliance with § 25.107(e)(3), some guidance relative to the airspeed attained at the 35-foot height during the associated flight test is necessary. As this requirement only specifies an early rotation (VR-5 knots), it is interpreted that pilot technique is to remain the same as normally used for a one-engine-inoperative condition. With these considerations in mind, it is apparent that the airspeed achieved at the 35-foot point can be somewhat below the normal scheduled V2 speed.
However, the amount of permissible V2 speed reduction should be limited to a reasonable amount as described below.
4.2.9.2.2 These test criteria apply to all unapproved, new, basic model airplanes.
They also apply to previously approved airplanes when subsequent testing is warranted. However, for those airplanes where these criteria are more stringent than those previously applied, consideration will be given to permitting some latitude in the test criteria.
4.2.9.2.3 In conducting the flight tests required by § 25.107(e)(3), the test pilot should use the normal/natural rotation technique associated with the use of scheduled takeoff speeds for the airplane being tested. Intentional tail or tail skid contact is not considered acceptable. Non-damaging contact due to inadvertent over-rotation is acceptable provided there is a prompt recovery to the normal one-engine-inoperative takeoff pitch attitude.
Further, the airspeed attained at the 35-foot height during this test should not be less than the scheduled V2 value minus 5 knots. These speed limits should not be considered or used as target V2 test speeds, but rather are intended to provide an acceptable range of speed departure below the scheduled V2 value. To ensure flight test safety, the maximum angle-ofattack, as a function of height above ground expected for this maneuver, should be confirmed to either fall below those previously demonstrated by VMU tests, or provide conservative margin to predicted in-ground-effect stall angle-of-attack as a function of height above ground (see Figure 4-A).
Note: experience has shown that the lowest margin to in-ground-effect stall angle-of-attack occurs in the vicinity of liftoff and that asymmetric flight conditions may adversely affect the stall angle-of-attack.
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AC 25-7D CHG 1
4.2.9.2.4 In this test, the simulated engine failure should be accomplished sufficiently in advance of the VR test speed to allow for engine spin-down, unless this would be below the VMCG, in which case VMCG should govern.
The normal one-engine-inoperative takeoff distance may be analytically adjusted to compensate for the effect of the early power or thrust reduction. Further, in those tests where the airspeed achieved at the 35-foot height is slightly less than the V2-5 knots limiting value, it will be permissible, in lieu of conducting the tests again, to analytically adjust the test distance to account for the excessive speed decrement.
4.2.9.3 All-Engines-Operating Tests.
4.2.9.3.1 Section 25.107(e)(4) states that there must not be a “marked increase” in the scheduled takeoff distance when reasonably expected service variations such as early and excessive rotation and out-of-trim conditions are encountered. This has been interpreted as requiring takeoff tests with all engines operating with:
A lower than scheduled rotation speed, and Out-of-trim conditions, but with rotation at the scheduled VR speed.
Note: The expression “marked increase” in the takeoff distance is considered to be any amount in excess of 1 percent of the scheduled takeoff distance. Thus, the tests should not result in field lengths more than 101 percent of the takeoff field lengths calculated in accordance with the applicable requirements of part 25 for presentation in the AFM.
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AC 25-7D CHG 1
4.2.9.3.2 For the early rotation condition with all engines operating, and at a weight as near as practicable to the maximum sea level standard day takeoff weight limit, it should be shown by tests that when the airplane is rotated at a speed below the scheduled VR, no “marked increase” in the scheduled AFM field length will result. For these tests, the airplane should be rotated at a speed equal to the scheduled VR minus 7 percent or the scheduled VR minus 10 knots, whichever results in the higher rotation speed. Tests should be conducted at (1) a rapid rotation rate to the normal takeoff attitude, and, as a separate set of tests, and (2) an over-rotation of 2° above the normal attitude following liftoff at a normal rotation rate. For this requirement, the rapid rotation rate achievable at VR-10 kt (or -7%) depends on the airplane configuration, type of pitch controller, flight control system design and the normal takeoff procedure. The rotation rate need not be increased beyond the point that prevents capturing the normal takeoff rotation attitude without using exceptional piloting skill or strength. For tests using over-rotations, the resulting increased pitch attitude should be maintained until the airplane is out of ground effect.
Tail strikes during this demonstration are acceptable if they are minor and do not result in unsafe conditions. The maximum angle-of-attack as a function of height above ground expected for both of these maneuvers should be confirmed to either fall below those previously demonstrated by flight tests or provide conservative margin to the predicted in-groundeffect stall angle-of-attack as a function of height above ground (see Figure 4-A).
Note: Experience has shown that the lowest margin to in-ground-effect stall angle-of-attack occurs in the vicinity of liftoff.
4.2.9.3.3 For reasonably expected out-of-trim conditions with all engines operating and as near as practicable to the maximum weight allowed under sea level standard day conditions, it should be shown that there will not be a “marked increase” in the scheduled AFM takeoff distance when rotation is initiated in a normal manner at the scheduled VR speed. The amount of mistrim should be the maximum mistrim that would not result in a takeoff configuration warning, including taking into account the takeoff configuration warning system rigging tolerance. It is permissible to accept an analysis in lieu of actual testing if the analysis shows that the out-of-trim condition would not present unsafe flight characteristics or a “marked increase” in the scheduled AFM field lengths.
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AC 25-7D CHG 1
4.2.9.3.4 Section 25.107(e)(4) also states that the reasonably expected variations in service from the established takeoff procedures for the operation of the airplane may not result in unsafe flight characteristics. For example, for an airplane loaded to obtain a forward CG position and mistrimmed for an aft CG loading, it may not be possible to rotate at the normal operating speeds due to excessive control force or lack of primary pitch control authority.
This may result in an excessive delay in accomplishing the rotation. Such a condition would be considered an unsafe flight characteristic. Similarly, for an airplane loaded to obtain an aft CG position and mistrimmed for a forward CG loading, it may not be possible to readily arrest a self-rotating tendency. This rotation, if abrupt enough and rapid enough, could lead to stall. Qualitative assessments should be made by the test pilot in the following takeoff tests with all engines operating:
1. The test pilot should determine that no unsafe characteristics exist with the airplane loaded to the forward CG limit and the stabilizer mistrimmed in the airplane nose-down direction. The amount of mistrim should be the maximum mistrim that would not result in a configuration warning (including taking into account takeoff warning system tolerances). Rotation should be initiated at the scheduled rotation speed for the airplane weight and ambient conditions. Unsafe characteristics include an excessive pitch control force to obtain normal airplane response or an excessive time to achieve perceptible rotation.
2. The test pilot should determine that no unsafe characteristics exist with the airplane loaded to the aft CG limit and the stabilizer mistrimmed in the airplane nose-up direction. The amount of mistrim should be the maximum mistrim that would not result in a configuration warning (including taking into account takeoff warning system tolerances). The airplane should be rotated at the scheduled rotation speed for the airplane weight and ambient conditions. Unsafe characteristics include an abrupt self-rotating tendency that cannot be checked with normal control input, or an excessive pitch control force required to maintain the airplane in the normal pitch attitude prior to the scheduled rotation speed or during rotation and initial climb.
3. For the tests described in paragraphs 1 and 2 above, the flight characteristics should be assessed at the most critical combinations of airplane weight, wing flap position and engine power or thrust for the out of trim position being considered.
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