4-13 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.
4.2.8.2.4 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.
4.2.8.3 All-Engines-Operating Tests.
4.2.8.3.1 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.
4.2.8.3.2 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 (2) an over-rotation of 2° above normal attitude after liftoff at the normal rotation rate. For tests using over rotations, the resulting increased pitch attitude should be maintained until the airplane is out of
4-14 ground effect. Tail strikes during this demonstration are acceptable if they are minor and do not result in unsafe conditions.
4.2.8.3.3 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.
4.2.8.3.4 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
4-15 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.
4.2.8.4 Stall Warning during Takeoff Speed Tests.
The presumption is that if an operational pilot was to make an error in takeoff speeds that resulted in an encounter with stall warning, the likely response would be to recover aggressively to a safe flight condition rather than trying to duplicate the AFM takeoff flight path. Therefore, the activation of any stall warning devices, or the occurrence of airframe buffeting during takeoff speed testing, is unacceptable.
4.2.8.5 Stick Forces during Takeoff Speed Tests.
According to § 25.143(a)(1) and (b), stick forces to initiate rotation and continue the takeoff during takeoff flight testing must comply with the control force limits of § 25.143(d). This includes the mistrim takeoff tests described in paragraphs 1 and 2 (on page 4-14) to show compliance with § 25.107 (e)(4), which are considered to represent probable operating conditions under § 25.143(b). Stick forces should be those that result from using the takeoff procedures established by the manufacturer for use in operational service in accordance with § 25.101(f) and must comply with § 25.101(h).
4.2.9 Procedures: Section 25.107(f)—Liftoff Speed (VLOF).
4.2.9.1 VLOF is defined as the calibrated airspeed at which the airplane first becomes airborne (i.e., no contact with the runway). This allows comparison of liftoff speed with tire limit speed. VLOF differs from VMU in that VMU is the minimum possible VLOF speed for a given configuration, and depending upon landing gear design, VMU liftoff is shown to be the point where all of the airplane weight is being supported by airplane lift and thrust forces and not any portion by the landing gear. For example, after the VMU speed is reached, a truck tilt actuator may force a front or rear wheel set to be in contact with the runway, even though the liftoff is in progress by virtue of lift being greater than weight.
4.2.9.2 The maximum ground speed at liftoff, considering the entire takeoff operating envelope and taking into account 50 percent of the headwind and 150 percent of the tailwind, in accordance with § 25.105(d)(1), must not exceed the tire speed rating established under § 25.733(a) or (c).
4-16
4.3 Accelerate-Stop Distance—§ 25.109.
4.3.1 Explanation.
4.3.1.1 The accelerate-stop distance is the horizontal distance from a reference point on the airplane at initial brake release to that same reference point after the airplane is brought to a stop.
4.3.1.2 This section describes test demonstrations and data expansion methods necessary to determine accelerate-stop distances for publication in the FAA-approved AFM, as required by § 25.1583(h) (by reference to § 25.1533). Amendment 25-92 revised some aspects of the part 25 accelerate-stop criteria and added new requirements related to the stopping capability of the airplane as affected by brake wear and wet runways. The changes imparted to the accelerate-stop requirements by amendment 25-92 are listed below. (For other material related to the use of accelerate-stop distances, see 14 CFR parts 121 and 135.)
4.3.1.2.1 Section 25.101(i) was added to require accelerate-stop distances to be determined with all the airplane wheel brake assemblies at the fully worn limit of their allowable wear range.
4.3.1.2.2 Section 25.105(c)(1) was revised to require takeoff data to be determined for wet, in addition to dry, hard surfaced runways. At the applicant’s option, takeoff data may also be determined for wet runways that have grooved or porous friction course surfaces.
4.3.1.2.3 Section 25.107(a)(2) was revised to remove the reference to “takeoff decision speed” from the definition of V1. V1 is the speed by which the pilot has already made the decision to either continue or reject the takeoff and, if the latter, has initiated the first action to stop the airplane.
4.3.1.2.4 Section 25.109 was revised to add a requirement to determine accelerate-stop distances for wet runways. Additionally, the requirement for the AFM expansion to include two seconds of continued acceleration beyond V1, with the operating engines at takeoff power or thrust, as introduced by amendment 25-42, was replaced with a distance increment equivalent to two seconds at V1. Also, the text of § 25.109(a) was modified to clarify that the accelerate-stop distances must take into account the highest speed reached during the rejected takeoff maneuver, including, as applicable, speeds higher than V1.
4.3.1.2.5 Section 25.109(f) was added to permit credit for the use of reverse thrust in determining wet runway accelerate-stop distances (subject to the requirements of § 25.109(e)) and to explicitly deny reverse thrust credit for determining dry runway accelerate-stop distances.
4-17
4.3.1.2.6 Section 25.109(i) was added to require a maximum brake energy accelerate-stop test to be conducted with not more than 10 percent of the allowable brake wear range remaining on each individual wheel-brake assembly.
4.3.1.2.7 Section 25.735(h) was added to require the maximum rejected takeoff brake energy absorption capacity rating used during qualification testing to the applicable TSO to be based on the fully worn limit of the brake’s allowable wear range.
Note: Section 25.735 was revised by amendment 25-107, which moved the rejected takeoff kinetic energy rating requirements into § 25.735(f).
4.3.1.2.8 Section 25.1533(a)(3) was revised to add runway surface condition (dry or wet) as a variable that must be accounted for in establishing minimum takeoff distances. Section 25.1533(a)(3) was also revised to allow wet runway takeoff distances on grooved and porous friction course (PFC) runways to be established as additional operating limitations, but approval to use these distances is limited to runways that have been designed, constructed, and maintained in a manner acceptable to the FAA Administrator.
4.3.2 Applicable Regulations.
The applicable part 25 regulations are § 25.109, and the following:
Section 25.101(f) regarding airplane configuration and procedures.
Section 25.101(h) regarding pilot action time delay allowances.
Section 25.101(i) regarding worn brake stopping performance.
Section 25.105 regarding takeoff configuration and environmental and runway conditions.
Section 25.107(a)(l) and (a)(2) regarding V1 and VEF speed definitions.
Section 25.735 regarding brakes and braking systems.
Section 25.1301 regarding function and installation.
Section 25.1309 regarding equipment, systems, and installation.
Section 25.1533 regarding additional operating limitations—maximum takeoff weights and minimum takeoff distances.
Section 25.1583(h) regarding AFM operating limitations.
Section 25.1587 regarding AFM performance information.
4.3.3 Procedures: General.
The following paragraphs provide guidance for accomplishing accelerate-stop flight tests and expanding the resulting data for the determination of AFM performance information.
4-18
4.3.4 Procedures: Accelerate-Stop Testing.
The following guidance applies to turbine-powered airplanes with and without propellers. Guidance regarding flight testing applies only to dry runway accelerate-stop distances. Guidance for expanding the flight test data to determine AFM distances applies to both dry and wet runways, unless otherwise noted. Further guidance for determining wet runway accelerate-stop distances is provided in paragraph 4.3.7 of this AC.
4.3.4.1 In order to establish a distance that would be representative of the distance needed in the event of a rejected takeoff, where the first action to stop the airplane is taken at V1, a sufficient number of test runs should be conducted for each airplane configuration specified by the applicant. (For intermediate configurations, see paragraph 3.1 of this AC.)
4.3.4.2 The guidance outlined in paragraph 4.3.6 of this AC describes how to include allowances for any time delays, as required by § 25.101(h)(3), for the flightcrew to accomplish the rejected takeoff operating procedures.
4.3.4.3 Section 25.101(i) states that the accelerate-stop distances must be determined with all the airplane wheel-brake assemblies at the fully worn limit of their allowable wear range. The fully worn limit is defined as the maximum amount of wear allowed before the brake is to be removed from the airplane for overhaul. The allowable wear should be defined in terms of a linear dimension in the axial direction, which is typically determined by measuring the wear pin extension.
4.3.4.3.1 The only accelerate-stop test that must be conducted at a specific brake wear state is the maximum brake kinetic energy demonstration, which must use brakes that have no more than 10 percent of the allowable brake wear range remaining, as required by § 25.109(i). (See paragraph 4.3.5.3 of this AC). The remainder of the accelerate-stop tests may be conducted with the brakes in any wear state as long as a suitable combination of airplane and dynamometer tests is used to determine the accelerate-stop distances corresponding to fully worn brakes. For example, dynamometer testing may be used to determine whether there is a reduction in brake performance from the wear state used in the airplane tests to a fully worn brake. The airplane test data could then be adjusted analytically for this difference without additional airplane testing.
4.3.4.3.2 Either airplane-worn or mechanically-worn brakes (i.e., machined or dynamometer worn) may be used. If mechanically-worn brakes are used, it should be shown that they can be expected to provide similar results to airplane-worn brakes. This comparison can be based on service experience on the test brake or an appropriate equivalent brake, or on dynamometer wear test data when service data are unavailable.
4-19
4.3.4.4 Section 25.109(f)(1) denies credit for the use of reverse thrust as a decelerating means in determining the accelerate-stop distance for a dry runway. This provision applies to both turbine engine and propeller engine reverse thrust (but not to any drag resulting from the ground idle power setting for a propeller engine). Credit for the additional deceleration available from reverse thrust is permitted for wet runway accelerate-stop distances, provided the thrust reverser system is shown to be safe, reliable, capable of giving repeatable results, and does not require exceptional skill to control the airplane. (See paragraph 4.3.7.10 of this AC for guidance related to obtaining accelerate-stop performance credit for reverse thrust on wet runways.)
4.3.4.5 The accelerate-stop test runs should be conducted at weight/speed combinations that will provide an even distribution of test conditions over the range of weights, speeds, and brake energies for which takeoff data will be provided in the AFM. The effects of different airport elevations can be simulated at one airport elevation, provided the braking speeds employed are relevant for the range of airplane energies to be absorbed by the brakes. The limiting brake energy value in the AFM should not exceed the maximum demonstrated in these tests or the maximum for which the brake has been approved. (See paragraph 4.3.5 of this AC for further guidance related to tests and analyses for the demonstration of the maximum brake energy absorption capability.)
4.3.4.6 The V1 speeds used in the accelerate-stop tests need not correspond precisely to the AFM values for the test conditions since it may be necessary to increase or decrease the AFM V1 speed to investigate fully the energy range and weight envelope.
4.3.4.7 A total of at least six accelerate-stop flight tests should be conducted.
Unless sufficient data are available for the specific airplane type showing how braking performance varies with weight, kinetic energy, lift, drag, ground speed, torque limit, etc., at least two tests should be conducted for each configuration when the same braking coefficient of friction is being claimed for multiple aerodynamic configurations. These tests should be conducted on smooth, hard surfaced, dry runways.
4.3.4.8 For approval of dispatch capability with anti-skid inoperative, nose wheel brakes or specified main wheel-brake(s) inoperative, automatic braking systems, etc., a full set of tests, as described in paragraph 4.3.4.7 above, should normally be conducted. A lesser number of tests may be accepted for “equal or better” demonstrations, to establish small increments or if adequate conservatism is used during testing.
4.3.4.9 Either ground or airborne instrumentation should include means to determine the horizontal distance time-history.
4-20
4.3.4.10 The wind speed and direction relative to the test runway should be determined and corrected to a height corresponding to the approximate height of the mean aerodynamic chord. (See paragraph 3.1 of this AC.)
4.3.4.11 The accelerate-stop tests should be conducted in the following configurations:
4.3.4.11.1 Heavy to light weight as required.
4.3.4.11.2 Most critical CG position.
4.3.4.11.3 Wing flaps in the takeoff position(s).
4.3.4.11.4 Tire pressure: before taxi and with cold tires, set to the highest value appropriate to the takeoff weight for which approval is being sought.
4.3.4.11.5 Engine idle power or thrust: set at the recommended upper limit for use on the ground or the effect of maximum ground idle power or thrust may be accounted for in data analyses. For maximum brake energy and fuse plug no-melt tests, data analysis may not be used in place of maximum ground idle power or thrust.
4.3.4.12 Engine power or thrust should be appropriate to each segment of the rejected takeoff and should include accounting for power or thrust decay rates (i.e., spin down) for failed or throttled back engines.
4.3.4.12.1 Turbojet Powered Airplanes.
For AFM calculation purposes, the critical engine failure accelerate-stop data may be based on the failed engine spinning down to a windmilling condition.
Note: If, due to the certification basis of the airplane, all-engine-accelerate-stop distances are not being considered, the one-engine-inoperative AFM distances should be based on the critical engine failing to maximum ground idle power or thrust rather than the windmilling condition.
4.3.4.12.2 The power or thrust from the operative engine(s) should be consistent with a throttle chop to maximum ground idle power or thrust. For determining the all-engines-operating dry runway accelerate-stop AFM distances, the stopping portion should be based on all engines producing maximum ground idle power or thrust (after engine spin down), as noted in paragraph 4.3.4.11.5 above. The accelerate-stop tests may be conducted with either concurrent or sequential throttle chops to idle power or thrust as long as the data are adjusted to take into account pilot reaction time, and any control, system, or braking differences (e.g., electrical or hydraulic/mechanical transients associated with an engine failing to a windmilling condition resulting in reduced braking effectiveness). Test
4-21 data should also be analytically corrected for any differences between maximum ground idle power or thrust and the idle power or thrust level achieved during the test. For the criteria relating to reverse thrust credit for wet runway accelerate-stop distances, see paragraph 4.3.7.10 of this AC.
4.3.4.12.3 Turbopropeller-Powered Airplanes.
For the one-engine-inoperative accelerate-stop distances, the critical engine’s propeller should be in the position it would normally assume when an engine fails and the power levers are closed. For dry runway one-engine-inoperative accelerate-stop distances, the high drag groundidle position of the operating engines’ propellers (defined by a pitch setting that results in not less than zero total thrust, i.e., propeller plus jet thrust, at zero airspeed) may be used provided adequate directional control is available on a wet runway and the related operational procedures comply with § 25.101(f) and (h). Wet runway controllability may either be demonstrated by using the guidance available in paragraph 4.3.7.10.6 of this AC at the appropriate power level, or adequate control can be assumed to be available at ground idle power if reverse thrust credit is approved for determining the wet runway accelerate-stop distances. For the all-engines-operating accelerate-stop distances on a dry runway, the high drag ground-idle propeller position may be used for all engines (subject to § 25.101(f) and (h)). For the criteria relating to reverse thrust credit for wet runway accelerate-stop distances, see paragraph 4.3.7.10 of this AC.
4.3.4.13 System transient effects (e.g., engine spin-down, brake pressure ramp-up, etc.) should be determined and properly accounted for in the calculation of AFM accelerate-stop distances. (See paragraph 4.3.6.10 of this AC.)
4.3.5 Procedures: Maximum Brake Energy Testing.
The following paragraphs describe regulatory requirements and acceptable test methods for conducting an accelerate-stop test run to demonstrate the maximum energy absorption capability of the wheel brakes.
4.3.5.1 The maximum brake energy accelerate-stop demonstration should be conducted at not less than the maximum takeoff weight. It should be preceded by at least a 3-mile taxi with all engines operating at maximum ground idle power or thrust, including three full stops using normal braking. Following the maximum brake energy stop, it will not be necessary to demonstrate the airplane’s ability to taxi.
4.3.5.2 Section 25.735(f)(2) requires the maximum kinetic energy accelerate-stop absorption capability of each wheel, tire, and brake assembly to be determined. It also requires dynamometer testing to show that the wheel, brake, and tire assembly is capable of absorbing not less than this level of kinetic energy throughout the defined wear range of the brake. The calculation of maximum brake energy limited takeoff weights and speeds,
4-22 for presentation in the AFM performance section, therefore should be based on the most critical wear range of the brake.
4.3.5.3 Section 25.109(i) requires a flight test demonstration of the maximum brake kinetic energy accelerate-stop distance to be conducted with not more than 10 percent of the allowable brake wear range remaining on each of the airplane wheel-brakes. The 10 percent allowance on the brake wear state is intended to ease test logistics and increase test safety, not to allow the accelerate-stop distance to be determined with less than fully worn brakes. If the brakes are not in the fully worn state at the beginning of the test, the accelerate-stop distance should be corrected as necessary to represent the stopping capability of fully worn brakes.
4.3.5.4 The maximum airplane brake energy allowed for dispatch should not exceed the value for which a satisfactory after-stop condition exists, or the value documented under the applicable TSO (or an acceptable equivalent), whichever value is less. A satisfactory after-stop condition is defined as one in which fires are confined to tires, wheels, and brakes, such that progressive engulfment of the rest of the airplane would not occur during the time of passenger and crew evacuation. The application of firefighting means or artificial coolants should not be required for a period of 5 minutes following the stop.
4.3.5.5 Landings are not an acceptable means for demonstrating the maximum rejected takeoff brake energy. Though permitted in the past, service experience has shown that methods used to predict brake and tire temperature increases that would have occurred during taxi and acceleration, as specified in paragraph 4.3.5.1 of this AC, were not able to accurately account for the associated energy increments.
4.3.6 Procedures: Accelerate-Stop Time Delays.
4.3.6.1 Section 25.101(h) requires allowance for time delays in the execution of procedures. Amendment 25-42 (effective March 1, 1978) amended the airworthiness standards to clarify and standardize the method of applying these time delays to the accelerate-stop transition period. Amendment 25-42 also added the critical engine failure speed, VEF, and clarified the meaning of V1 with relation to VEF. The preamble to amendment 25-42 states that “V1 is determined by adding to VEF (the speed at which the critical engine is assumed to fail) the speed gained with the critical engine inoperative during the time interval between the instant at which the critical engine is failed and the instant at which the test pilot recognizes and reacts to the engine failure, as indicated by the pilot’s application of the first retarding means during accelerate-stop tests.” Thus it can be seen that V1 is not only intended to be at the end of the decision process, but it also includes the time it takes for the pilot to perform the first action to stop the airplane. (See appendix C of this AC for further discussion on the
4-23 historical development of accelerate-stop time delays.) The purpose of the time delays is to allow sufficient time (and distance) for a pilot, in actual operations, to accomplish the procedures for stopping the airplane. The time delays are not intended to allow extra time for making a decision to stop as the airplane passes through V1. Since the typical transport category airplane requires three pilot actions (i.e., brakes-throttles-spoilers) to achieve the final braking configuration, amendment 25-42 defined a two-second time period, in § 25.109, to account for delays in activating the second and third deceleration devices. Amendment 25-92 (effective March 20, 1998) redefined, and reinterpreted the application of that two-second delay time as a distance increment equivalent to two seconds at V1. No credit may be taken for system transient effects (e.g., engine spin-down, brake pressure ramp-up, etc.) in determining this distance. The following paragraphs provide guidance related to the interpretation and application of delay times to show compliance with the accelerate-stop requirements of amendment 25-92.
4.3.6.2 Figure 4-1 below presents a pictorial representation of the accelerate-stop time delays considered acceptable for compliance with § 25.101(h) as discussed above.
Figure 4-1. Accelerate-Stop Time Delays Initiation of first pilot action Initiation of second pilot action Initiation of third pilot action Engine failure
V 1 V EF t act 1 t act 1 Event Demonstrated Time Delays Flight Manual Expansion Time Delays Initiation of subsequent pilot actions t act 4 n t act + 1 sec.
t act 2 t act 2 t act 3 t act 3 Distance equivalent to 2 sec. at V 1
4.3.6.3 VEF is the calibrated airspeed selected by the applicant at which the critical engine is assumed to fail. The relationship between VEF and V1 is defined in § 25.107.
4.3.6.4 Δtact 1 is the demonstrated time interval between engine failure and initiation of the first pilot action to stop the airplane. This time interval is defined as beginning at the instant the critical engine is failed and ending when the pilot recognizes and reacts to the engine failure, as indicated by the pilot’s first action taken to stop the airplane during accelerate-stop tests. A sufficient number of demonstrations should be conducted using
4-24 both applicant and FAA test pilots to assure that the time increment is representative and repeatable. The pilot’s feet should be on the rudder pedals, not the brakes, during the tests. For AFM data expansion purposes, in order to provide a recognition time increment that can be executed consistently in service, this time increment should be equal to the demonstrated time or one second, whichever is greater. If the airplane incorporates an engine failure warning light, the recognition time includes the time increment necessary for the engine to spool down to the point of warning light activation, plus the time increment from light “on” to the first pilot action to stop the airplane.
4.3.6.5 Δtact 2 is the demonstrated time interval between initiation of the first and second pilot actions to stop the airplane.
4.3.6.6 Δtact 3 is the demonstrated time interval between initiation of the second and third pilot actions to stop the airplane.
4.3.6.7 Δtact 4→n is the demonstrated time interval between initiation of the third and fourth (and any subsequent) pilot actions to stop the airplane. For AFM expansion, a one-second reaction time delay to account for inservice variations should be added to the demonstrated time interval between the third and fourth (and any subsequent) pilot actions. If a command is required for another crewmember to initiate an action to stop the airplane, a two-second delay, in lieu of the one-second delay, should be applied for each action. For automatic deceleration devices that are approved for performance credit for AFM data expansion, established systems actuation times determined during certification testing may be used without the application of the additional time delays required by this paragraph.
4.3.6.8 The sequence of pilot actions may be selected by the applicant, but it must match the sequence established for operation in service, as prescribed by § 25.101(f). If, on occasion, the specified sequence is not achieved during testing, the test need not be discarded; however, sufficient testing should be conducted to establish acceptable values of Δtact.
4.3.6.9 Section 25.109(a)(1)(iv) and (a)(2)(iii) require the one-engine-inoperative and all-engines-operating accelerate-stop distances, respectively, to include a distance increment equivalent to two seconds at V1. (Although the requirement for the distance increment equivalent to two seconds at V1 is explicitly stated in the “dry runway” criteria of § 25.109, it is also applied to the “wet runway” accelerate-stop distances by reference in § 25.109(b).) This distance increment is represented pictorially on the right side of the “Flight Manual Expansion Time Delays” presentation in figure 4-1 below, and in the speed versus distance plot of figure 4-2 below, on the following page. The two-second time period is only provided as a method to calculate the required distance increment, and is