o Takeoff surface press ure altitude (hp) = 2,000 ft.
o Airport std. temp. abs. (T S) = 11oC+273.2o = 284.2oK o Airport ambient temp. abs. (T AM) = -20oC+273.2o = 253.2oK o Geometric height required ( ∆h) = 1,700 ft. above the takeoff surface Find:
o Pressure a ltitude increment (∆hp) above the takeoff surface ∆hp = ∆h(TS/TAM) = 1,700 ft. (284.2oK/253.2oK) ∆hp = 1,908 ft.
g. Section 25.111(c)(2) - Takeoff Path Speed .
(1) Explanation.
(i) It is intended that the airplane be flown at a constant i ndicated airspeed to at least 400 ft. above the takeoff surface. This speed must meet the constraints on V 2 of §§ 25.107(b) and (c).
(ii) The specific wording of § 25.111(c)(2) should not be construed to imply that above 400 ft. the airspeed may be reduced below V 2 , but instead that acceleration may be commenced.
(2) Procedures .
(i) For those airplanes that take advantage of reduced stall speeds at low pressure altitude, the scheduling of V2 should not be factored against the stall speed obtained at the takeoff surface pressure altitude.
Such a procedure would result in a reduced stall speed margin during the climb, which would be contrary to the intent of § 25.107(b).
(ii) For those airplanes mentioned in paragraph (i), above, the V 2 should be constrained, in addition to the requirements of §§ 25.107(b) and (c), by the stall speed 1,500 ft. above the takeoff surface. Weight reduction along the takeoff path, due to fuel burn, may be considered in the calculation of the stall speed ratios, provided it is well established. However, many applicants have measured stall speeds at 10,000 to 15,000 ft., which provides stall margin conservatism at lower takeoff field pressure altitudes.
h. Section 25.111(c)(3) - Required Gradient .
(1) Explanation. None.
(2) Procedures . None.
i. Section 25.111(c)(4) - Configuration Changes .
(1) Explanation.
(i) The intent of this requirement is to permit only those crew actions that are conducted routinely to be used in establishing the one-engine-inoperative takeoff path. The power levers may only be adjusted early during the takeoff roll, as discussed in paragraph 12b(2), and then left fixed until at least 400 ft. above the takeoff surface.
(ii) Simulation studies and accident investigations h ave shown that when heavy workload occurs in the cockpit, as with an engine failure during takeoff, the crew might not advance the operative engines to avoid the ground, even if the crew knows the operative engines have been set at reduced power. This same finding applies to manually feathering a propeller. The landing gear may be retracted, however, as this is accomplished routinely once a positive rate of climb is observed. This also establishes the delay time to be used for data expansion purposes.
(2) Procedures .
(i) To permit the takeoff to be conducted using less than rated power, automatic power advance devices have been approved. These devices are addressed in § 25.904, and the related performance requirements are described in Appendix I to Part 25 of the FAR.
(ii) To permit the takeoff to be based on a feathered propeller up to 400 ft. above the takeoff surface, automatic propeller feathering devices have been approved. Guidance related to performance credit for automatic propeller feathering devices, below 400 feet above the takeoff surface, is presented in paragraph 241 of this AC.
(iii) Drag reduction for a manually feathered propeller is permitted for flight path calculations only after reaching 400 ft. above the takeoff surface.
j. Section 25.111(d) - Takeoff Path Construction .
(1) Explanation. This regulation should not be construed to mean that the takeoff path be constructed entirely from a continuous demonstration or entirely from segments. To take advantage of ground effect, typical AFM takeoff paths utilize a continuous takeoff path from V LOF to the gear up point, covering the range of thrust-toweight ratios. From that point free air performance, in accordance with § 25.111(d)(2), is added segmentally. This methodology may yield an AFM flight path that is steeper with the gear down than up.
(2) Procedures . The AFM should include the procedures necessary to achieve this performance.
k. Section 25.111(d)(1) - Takeoff Path Segment Definition .
(1) Explanation. None.
(2) Procedures . None.
l. Section 25.111(d)(2) - Takeoff Path Segment Conditions .
(1) Explanation. The subject paragraph states “The weight of the airplane, the configuration, and the power or thrust setting must be constant throughout each segment and must correspond to the most critical condition prevailing in the segment.” The intent is that, for simplified analysis, the performance must be based on that value available at the most critical point in time during the segment, not that the individual variables (weight, approximate thrust setting, etc.) should each be picked at their most critical value and then combined to produce the performance for the segment.
(2) Procedures . The performance during the takeoff path segments should be obtained using one of the following methods:
(i) The critical level of performance as explained in paragraph (1);
(ii) The average performance during the segment; or
(iii) The actual performance variation during the segment.
m. Section 25.111(d)(3) - Segmented Takeoff Path Ground Effect .
(1) Explanation. This requirement does not intend the entire flight path to necessarily be based upon out-of-ground-effect performance simply because the continuous takeoff demonstrations have been broken into sections for data reduction expediency. For example, if the engine inoperative acceleration from V EF to VR is separated into a thrust decay portion and a windmilling drag portion, the climb from 35 ft. to gear up does not necessarily need to be based upon out-of-ground-effect performance. (Also see explanation under § 25.111(d) in paragraph 12j(1) of this AC.)
(2) Procedures . None
n. Section 25.111(d)(4) - Segmented Takeoff Path Check .
(1) Explanation. None.
(2) Procedures . If the construction of the takeoff path from brake release to out-of-ground-effect contains any portions that have been segmented (e.g., airplane acceleration segments with all-engines-operating and one-engine-inoperative), the path should be checked by continuous demonstrated takeoffs. A sufficient number of these, employing the AFM established takeoff procedures and speeds and covering the range of thrust-to-weight ratios, should be made to ensure the validity of the segmented takeoff path. The continuous takeoff data should be compared to takeoff data calculated by AFM data procedures but using test engine thrusts and test speeds.
o. Section 25.111(e) - Flight Path with Standby Power Rocket Engines . (RESERVED).
*13. TAKEOFF DISTANCE AND TAKEOFF RUN - § 25.113 .
a. Takeoff Distance on a Dry Runway - § 25.113(a) .
(1) The takeoff distance on a dry runway is the greater of the two distances depicted in (i) or (ii) below.
The distances indicated below are measured horizontally from the main landing gears at initial brake release to that same point on the airplane when the lowest part of the departing airplane is 35 ft. above the surface of the runway.
(i) The distance measured to 35 ft. with a critical engine failure occurring at V EF as shown in Figure
13-1. *
* FIGURE 13-1. TAKEOFF DISTANCE ON A DRY RUNWAY Critical Engine Fails at V EF *
(ii) One hundred fifteen (115) percent of the distance measured to the 35 ft. height above the takeoff surface with all-engines-operating as shown in Figure 13-2. In establishing the all-engines-operating takeoff distance, § 25.113(a)(2) requires the distance to be “...determined by a procedure consistent with § 25.111” (Takeoff Path). The interpretation of this statement is that the all-engines-operating takeoff distance should:
(A) Be based on the airplane reaching a speed of V 2 before it is 35 feet above the takeoff surface; and (B) Be consistent with the achievement of a smooth transition to the steady initial climb speed at a height of 400 feet above the takeoff surface.
(2) The takeoff procedure adopted should be re flected in the takeoff distance.
* b. Takeoff Distance on a Wet Runway - § 25.113(b) .
(1) The takeoff distance on a wet runway is the greater of the takeoff distance on a dry runway (using the dry runway V 1 speed), determined in accordance with paragraphs 13a(1)(i) and (ii) of this AC, or the distance on a wet runway using a reduced screen height (and the wet runway V 1 speed) as described in paragraph (2), below.
(2) The takeoff distance on a wet runway is determined as the horizontal distance the main landing gear travels from brake release to the point where the lowest part of the airplane is 15 ft. above the takeoff surface. The airplane must attain a height of 15 ft. above the takeoff surface before reaching the end of the runway in a manner that will allow V2 to be achieved before reaching a height of 35 ft. above the takeoff surface as shown in Figure 13-
3.
FIGURE 13-3. TAKEOFF DISTANCE ON A WET RUNWAY Critical Engine Fails at V EF
c. Takeoff Run - § 25.113(c) .
(1) Takeoff run is a term used for the runway length when the takeoff distance includes a clearway (i.e., where the accelerate-go distance does not remain entirely over the runway), and the takeoff run is either of the two distances depicted in (i) or (ii) below, whichever is greater. These distances are measured as described in § 25.113(a). When using a clearway to determine the takeoff run, no more than one half of the air distance from VLOF to V35 may be flown over the clearway.
(i) The distan ce from the start of the takeoff roll to the mid-point between liftoff and the point at which the airplane attains a height of 35 ft. above the takeoff surface, with a critical engine failure occurring at V EF, as shown in Figure 13-4. For takeoff on a wet runway, the takeoff run is equal to the takeoff distance (i.e., there is no clearway credit allowed on a wet runway *
* FIGURE 13-4. TAKEOFF RUN Critical Engine Fails at V EF *
(ii) One hundred fifteen (115) percent of the distance from the start of the takeoff roll to the midpoint between liftoff and the point at which the airplane attains a height of 35 ft. above the takeoff surface, with all engines operating, as shown in Figure 13-5. In establishing the all-engines-operating takeoff run, § 25.113(c)(2) requires the distance to be “...determined by a procedure consistent with § 25.111” (Takeoff Path). The interpretation of that statement is that the all-engines-operating takeoff run should:
(A) Be based on the airplane reaching a speed of V 2 before it is 35 feet above the takeoff surface; and (B) Be consistent with the achievement of a smooth transition to the steady initial climb speed at a height of 400 feet above the takeoff surface.
(2) There may be situations in which the one-engine-inoperative condition (paragraph 13c(1)(i)) would dictate one of the distance criteria, takeoff run (required runway) or takeoff distance (required runway plus clearway), while the all-engines-operating condition (paragraph 13c(1)(ii)) would dictate the other. Therefore, both conditions should always be considered.
(3) Clearway is defined in 14 CFR part 1 as a plane extending from the end of the runway with an upward slope not exceeding 1.25 percent, above which no object nor any terrain protrudes. For the purpose of establishing takeoff distances and the length of takeoff runs, the clearway is considered to be part of the takeoff surface extending with the same slope as the runway, and the 35 ft. height should be measured from that surface.
(4) The profile shows no fixed obstacle projecting above the clearway plane. However, the airport authorities must have control of the movable obstacles in this area to ensure that no flight will be initiated using a clearway unless it is determined with certainty that no movable obstacles will exist within the clearway when the airplane flies over.
14. TAKEOFF FLIGHT PATH - § 25.115 .
* a. Takeoff Flight Path - § 25.115(a) .
(1) Explanation. The takeoff flight path begins at the end of the takeoff distance and at a height of 35 ft.
above the takeoff surface, and ends when the airplane’s actual height is the higher of 1,500 ft. above the takeoff surface or at an altitude at which the configuration and speed have been achieved where the requirements of §
25.121(c) can be met. (See paragraph 12 of this AC (§ 25.111) for additional discussion.) Section 25.115(a) states that the takeoff shall be considered to begin at a height of 35 feet, recognizing that in the case of a wet runway the * *airplane will only be at a height of 15 feet. For takeoffs from wet runways, the actual airplane height will be 20 feet lower than the takeoff flight path determined under § 25.115. Therefore, the airplane will be 20 feet closer vertically to obstacles after taking off from a wet runway compared to taking off from a dry runway.
*
(2) Procedures .
FIGURE 14-1. TAKEOFF SEGMENTS & NOMENCLATURE
TAKEOFF FLIGHI PATH
• ACTUAL HITCHT ≥ 1500 FEET 1500 FEET PATH 2 TAKEOFF DISTANCE (LONGER ACTUAL HEIGHI ≥ 400 FEET + OF 1 ENG INOP TAKEOFF OR —
1.15 ALL ENG TAKEOFF) PATH I
ACTUAL HEICHTS ARE VEr VLOF GEAR RETRACTION COMPLETE RUNWAY ELEVATION REFERENCED TO AT END OF TAKEOFF
DISTANCE SECMENT* LANDING GEAR GROUND ROLL DOWN RETRACHON IST 2ND →4 ACCELFRATION RETRACTED FINAL
ENROUTE
FLAPS TAKEOFF RETRACTING (SEE NOTE) POSITION POWER TAKEOFF "ABOVE 400 FTTARUST CAN BE REDUCED THE REQUIREMENTS OF 25. 111(CY) CAN BE MET WITH LESS THAN TAKEOFF THRUST SEE NOTE CONTINUOUS MAXIUM AIRSPEED ACCELERATING ACCELERATING, 21.25 V;
ENGINES ALL OPERATINC ONE INOPERATTVE
PROPELLER TAKEOFF ONE AUTOFRATHERED OR WINDMILANG ONE FEATHERED UP TO 400 FEET 400 FEET OR CREATER Note: The final takeoff segment will usually begin with the airplane in the en route configuration and with maximum continuous thrust, but it is not required that these conditions exist until the end of the takeoff path when compliance with § 25.121(c) is shown. The time limit on takeoff thrust cannot be exceeded.
* Segments as defined by § 25.121.
b. Net Takeoff Flight Path - §§ 25.115(b) and (c).
(1) Explanation.
(1) The net takeoff flight path is the actual flight path diminished by a gradient of 0.8 percent for two-engine airplanes, 0.9 percent for three-engine airplanes, and 1.0 percent for four-engine airplanes.
(ii) For the level flight acceleration segment, these prescribed gradient reductions may be applied as an equivalent reduction in acceleration in lieu of reduction in net flight path. (See paragraph 12 (ref. § 25.111) of this AC for additional discussion.)
(iii) SR-422B, and § 121.189(d), require that no airplane may take off at a weight in excess of that shown in the AFM to correspond with a net takeoff flight path that clears all obstacles either by at least a height of 35 ft. vertically, or by at least 200 ft. horizontally within the airport boundaries, and by at least 300 ft. horizontally after passing beyond the boundaries.
(iv) With turns in the net takeoff flight path, obstacle clearance determination requires consideration of both radius of turn and climb gradient decrement. Radius of turn, for use in obstacle lateral separation, is not airplane dependent and is readily calculated from speed and bank angle. Climb gradient decrements, however, are airplane dependent. Climb gradient decrements for bank angles up to at least 15 degrees should be contained in the AFM.
(2) Procedures .
15. CLIMB: GENERAL - § 25.117.
a. Explanation. This section states the climb requirements of §§ 25.119 and 25.121 must be complied with at each weight, altitude, and ambient temperature within the operational limits established for the airplane and with the most unfavorable center of gravity for each configuration. When approval of an airplane for operation in known icing conditions is requested, compliance with the approach climb requirements of § 25.121(d), and landing climb requirements of § 25.119, should be demonstrated with residual ice accretions on unprotected areas of the airframe.
For further guidance on this subject see paragraph 231, “Performance Requirements for Flight in Icing Conditions,” in Chapter 8 of this AC.
b. Procedures . None.
16. LANDING CLIMB: ALL-ENGINES-OPERATING - § 25.119 .
a. Explanation. Section 25.119(a) states that the engines are to be set at the power or thrust that is available 8 seconds after initiating movement of the power or thrust controls from the minimum flight idle position to the goaround power or thrust setting. The procedures given below are for the determination of this maximum thrust for showing compliance with the climb requirements of § 25.119.
b. Procedures .
(1) The engines should be trimmed to the low side of the idle trim band, if applicable, as defined in the airplane maintenance manual. The effect of any variation in the idle fuel flow schedule for engines with electronic fuel controllers is typically negligible (but any such claim should be adequately substantiated).
(2) At the most adverse test altitude , not to exceed the maximum field elevation for which certification is sought plus 1,500 ft., and with the most adverse bleed configuration expected in normal operations, stabilize the airplane in level flight with symmetrical power on all engines, landing gear down, flaps in the landing position, at a speed of 1.3 VS0. Retard the throttle(s) of the test engine(s) to flight idle and determine the time needed to reach a stabilized r.p.m., as defined below, for the test engine(s) while maintaining level flight or the minimum rate of descent obtainable with the thrust of the remaining engine(s) not greater than maximum continuous thrust (MCT).
Engine flight idle r.p.m. is considered to be stabilized when the initial rapid deceleration of all rotors is completed.
This has usually been 8-20 seconds. This can be determined in the cockpit as the point where rapid movement of the tachometer ceases. For some airplanes it may be desirable to determine the deceleration time from plots of
r.p.m. versus time.
(3) For the critical air bleed configuration , stabilize the airplane in level flight with symmetric power on all engines, landing gear down, flaps in the landing position, at a speed of 1.3 V S0, simulating the estimated minimum climb-limited landing weights (goal is low airspeed for low idle r.p.m.) at an altitude sufficiently above the selected test altitude so that time to descend to the test altitude with the throttles closed equals the appropriate engine r.p.m. stabilization time determined in paragraph (2) above. Retard the throttles to the flight idle position and descend at 1.3 VS0 to approximately the test altitude. When the appropriate time has elapsed, rapidly advance the power or thrust controls to the go-around power or thrust setting. The power or thrust controls may first be advanced to the forward stop and then retarded to the go-around power or thrust setting. At the applicant’s option, additional less critical bleed configurations may be tested.
(4) The thrust that is available 8 seconds after the initiation of movement of the power or thrust controls from the minimum flight idle position, in accordance with paragraph (3) above, will be the maximum permitted for showing compliance with the landing climb requirements of § 25.119(a), and Section 4T. 119(a) of SR-422B (see Appendix 1) for each of the bleed combinations tested in accordance with paragraph (3) above. If AFM performance is presented such that there is no accountability for various bleed conditions, the thrust obtained with the most critical airbleed shall be used for landing climb performance for all operations. The effects of anti-ice bleed must be accounted for.
17. CLIMB: ONE-ENGINE-INOPERATIVE - § 25.121 .
a. Explanation. None.
b. Procedures .
(1) Two methods for establishing one-engine-inoperative climb performance follow:
(i) Reciprocal heading climbs are conducted at several thrust-to-weight conditions from which the performance for the AFM is extracted. These climbs are flown with the wings nominally level. Reciprocal climbs may not be necessary if inertial corrections (or another equivalent means) are applied to account for wind gradients.
(ii) Drag polars and one-engine-inoperative yaw drag data are obtained for expansion into AFM climb performance. These data are obtained with the wings nominally level. Reciprocal heading check climbs are conducted to verify the predicted climb performance. These check climbs may be flown with the wings maintained
in a near level attitude. Reciprocal climbs may not be necessary if inertial corrections (or another equivalent means) are applied to account for wind gradients.
(2) If full rudder with wings level cannot maintain constant heading, small bank angles into the operating engine(s), with full rudder, should be used to maintain constant heading. Unless the landing lights automatically retract with engine failure, testing should be conducted with the lights extended for § 25.121(a) Takeoff; landing gear extended, § 25.121(b) Takeoff; landing gear retracted, and § 25.121(d) Approach.
(3) The climb performance tests with landing gear extended, in accordance with § 25.121(a), may be conducted with the landing gear and gear doors in the position they finally achieve after “gear down” selection. The critical configuration for the landing gear extended climb is considered to be that which presents the largest frontal area to the local airflow. This would normally be with no weight on the landing gear (full strut extension and trucks tilted) and all gear doors open. However, since the takeoff path will be determined by measurement of continuous takeoffs, or checked by continuous takeoffs if constructed by the segmental method (Ref. § 25.111(d)), any nonconservatism arising from the gear doors “closed” climb data will be evident. Also, some measure of conservatism is added to the landing gear extended climb performance by the requirement of § 25.111(d)(3) for the takeoff path data to be based on the airplane’s performance without ground effect.
(4) If means, such as variable intake doors , are provided to control powerplant cooling air supply during takeoff, climb, and en route flight, they should be set in a position that will maintain the temperature of major powerplant components, engine fluids, etc., within the established limits. The effect of these procedures should be included in the climb performance of the airplane. These provisions apply for all ambient temperatures up to the highest operational temperature limit for which approval is desired. (Reference: § 25.1043)
(5) The latter parts of §§ 25.121(a)(1) and (b)(1) , which state “...unless there is a more critical power operating condition existing later along the flight path...” are intended to cover those cases similar to where a wet engine depletes its water and reverts to dry engine operation. This is not intended to cover normal altitude thrust lapse rates above the point where the landing gear is fully retracted. (Reference: Preamble to SR-422A)
(6) Section 25.121(d) requires that the stalling speed for the approach configuration, landing gear retracted, not exceed 110 percent of the stalling speed for the related landing configuration, landing gear extended.
This stall speed ratio requirement is to ensure that an adequate margin above the stall speed in the selected approach configuration is maintained during flap retraction. To achieve this stall speed spread requirement, it is permissible to arbitrarily increase the landing flap stalling speed, V S0, to show compliance. The AFM must, however, base the landing speed on the increased stalling speed, and the landing distance demonstrations and the AFM landing field length requirements must also be predicated on the increased speed. The stall warning requirements of § 25.207 must be established for the adjusted stalling speed. However, the § 25.203 stall characteristics requirements must still be met at the normal stall speed. (An alternative to raising the landing flap stall speed, V S0, is to simply increase the landing speed stall ratio to a value greater than 1.3.)
18. EN ROUTE FLIGHT PATHS - § 25.123 .
a. Explanation. This guidance is intended for showing compliance with the requirements of § 25.123 and application to the operating requirements of §§ 121.191 and 121.193, which specify the clearances over terrain and obstructions required of the net en route flight paths subsequent to the failure of one or two engines.
b. Procedures .
(1) Sufficient en route climb performance data should be presented in the AFM to permit the determination of the net climb gradient and the net flight path in accordance with §§ 25.123(b) and (c) for all gross weights, altitudes, and ambient temperatures within the operating limits of the airplane. This en route climb performance data should be presented for altitudes up to the all-engines-operating ceiling to permit the calculation of drift-down data in the event of an en route engine failure.
(2) Fuel Consumption Accountability . The effect of the variation of the airplane’s weight along the flight path due to the progressive consumption of fuel may be taken into account using fuel flow rates obtained from airplane manufacturers’ test data. If measured fuel flow data is unavailable, a conservative fuel flow rate not greater than 80 percent of the engine specification flow rate at maximum continuous thrust (MCT) may be used.
(3) The procedures and flight conditions upon which the en route flight path data are based should be provided to the flightcrew. Credit for fuel dumping, if available and included in the flightcrew procedures, may be used to achieve the performance capability presented in the AFM. A conservative analysis should be used in taking into account the ambient conditions of temperature and wind existing along the flight path. All performance should be based on the net flight path and with MCT on the operating engine(s).
19. LANDING - § 25.125 .
a. Explanation.
(1) The landing distance is the horizontal distance from the point at which the main gear of the airplane is 50 ft. above the landing surface (treated as a horizontal plane through the touchdown point) to the point at which the airplane is brought to a stop. (For water landings, a speed of approximately 3 knots is considered “stopped.”) In this AC, the distance is treated in two parts: the airborne distance from 50 ft. to touchdown, and the ground distance from touchdown to stop. The latter may be further subdivided into a transition phase and a full braking phase if the applicant prefers this method of analysis.
(2) The term VREF used in this AC means the landing threshold speed (i.e., speed at 50 ft. height) scheduled in the AFM for normal operations. The minimum value of V REF is specified in § 25.125(a)(2) as 1.3V S, which provides an adequate margin above the stall speed to allow for likely speed variations during an approach in low turbulence. If the landing demonstrations are unable to show the acceptability of the minimum approach speed, and the tests are predicated on the use of a V REF greater than the minimum 1.3 V S, the landing distance data presented in the AFM must be based upon the higher approach speed.
(3) The engines should be set to the high side of the flight idle trim band, if applicable, for the landing flight tests. The effect of any variation in the idle fuel flow schedule for engines with electronic fuel controllers is typically negligible (but any such claim should be adequately substantiated).
b. Procedures for Determination of the Airborne Distance . Three acceptable means of compliance are described in paragraphs (1), (2), and (3) below. These differ from the “traditional” method in which steep approaches and high touchdown sink rates were permitted. Such a demonstration of maximum performance is no longer considered acceptable. However, the distances obtained using that method have resulted in a satisfactory operational safety record. The methods given here allow credit for the amount of testing an applicant is prepared to conduct, such that if the method described in paragraph 19b(3) (the most complex) is chosen, distances typical of those from the “traditional” method should be obtained, but without incurring the associated risks during testing.
NOTE. If it is determined that the constraints on approach angle and touchdown rate-of-sink described in paragraphs (2) and (3), below, are not appropriate due to novel or unusual features of future transport category airplane design, new criteria may be established. Such a change would be acceptable only if it is determined that an equivalent level of safety to existing performance standards and operational procedures is maintained.
(1) Experience shows an upper bound to the Part 25 zero-wind airborne distances achieved in past certifications and, similarly, a minimum speed loss. These are approximated by the following:
Air Distance (feet) = 1.55 (V REF-80)1.35 +800 where VREF is in knots TAS Touchdown Speed = V REF-3 knots An applicant may choose to use these relationships to establish landing distance in lieu of measuring airborne distance and speed loss. If an applicant chooses to use these relationships, it must be shown by test or analysis that they do not result in air distances or touchdown speeds that are nonconservative.
(2) If an applicant chooses to measure airborne distance or time, at least six tests covering the landing weight range are required for each airplane configuration for which certification is desired. These tests should meet the following criteria: