10 8 DETERMINATION OF LANDING DISTANCE FOR TIME-OF-ARRIVAL LANDING PERFORMANCE ASSESSMENTS.
8.1 Landing Distance.
8.1.1 The landing distance consists of three segments—an airborne segment, a transition segment, and a final stopping configuration (full braking) segment, as shown in figure 1 below.
Figure 1. Landing Distance Segments VTD VAPP Transition Distance 50 Ft.
Full Braking DistanceAir Distance
8.1.2 The landing distance for a time-of-arrival landing performance assessment may be determined analytically from the landing performance model developed to show compliance with § 25.125. For the purposes of determining landing distance for time-of-arrival assessments, the model should be modified as described in the following paragraphs.
8.1.3 Changes in the airplane’s configuration, speed, power, and thrust used to determine the landing distance for time-of-arrival landing performance assessments should be made using procedures established by the data provider for operation in service. These procedures should—
• Be able to be consistently executed in service by crews of average skill;
• Use methods or devices that are safe and reliable; and
• Include allowance for any time delays that may reasonably be expected in service.
(See paragraphs 8.3.2, 8.3.3, and 8.3.4 of this AC.)
8.1.4 The procedures and assumptions used to develop the operational landing distances should be documented in the appropriate reference material.
8.2 Air Distance.
8.2.1 As shown in figure 1 of this AC, the air distance is the distance from a height of 50 feet above the landing surface to the point of main gear touchdown. This definition of the air distance is unchanged from that used for compliance with § 25.125. However, the air distance determined under § 25.125 may not be appropriate for use in making time-of-arrival landing performance assessments. Especially for airplanes for which the parametric method of determining the air distance was used as described in AC 25-7C, the air distances determined under § 25.125 may be shorter than the distance that the average pilot is likely to achieve in normal operations.
Note: AC 25-7C states the air distance computed using the parametric method should only be used in conjunction with the factor as described in § 121.195(b) or (c);
§ 135.385(b), (c), or (f); or equivalent.
8.2.2 There are reasons why the air distance determined under § 25.125 might be shorter than the distance the average pilot is likely to achieve in normal operations. First, the parametric method of determining the air distance presented in AC 25-7C, used by some manufacturers to provide landing distance in their AFMs allows the air distance to be based on a steeper-than-normal approach angle of -3.5°, followed by a flare in which the touchdown rate of descent can be as high as 8 feet per second. Second, the § 25.125 air distance is based on beginning at a speed of VREF, whereas the operating procedures may recommend a higher speed, particularly when headwinds are present. Third, the philosophy followed by some manufacturers during the certification process is to determine the maximum capability of the airplane.
8.2.3 The air distance used for any individual landing at any specific runway is a function of the runway approach guidance, runway slope, use of any airplane features or equipment (for example, heads-up guidance, autoflight systems, etc.), pilot technique, and the inherent flare characteristics of the specific airplane.
8.2.4 Unless the air distance used for compliance with § 25.125 is representative of an average pilot who is flying in normal operations (see paragraph 8.2.5 below), the air distance used for time-of-arrival landing performance assessments should be determined analytically as the distance traversed over a time period of 7 seconds at a speed of 98 percent of the recommended speed over the landing threshold, also referred to as the final approach speed (VAPP). This represents a flare time of 7 seconds and a touchdown speed (VTD) of 96 percent of VAPP. VAPP should be consistent with the TC holder’s recommended procedures and training material, including any speed additives, such as may be used for winds or icing. The effect of higher speeds, to account for variations that occur in operations or through the operating procedures of individual operators, should also be provided.
8.2.5 If the air distance is determined directly from flight test data instead of the analytical method provided in paragraph 8.2.4 above, the flight test data should meet the following criteria:
8.2.5.1 Procedures should be used that are consistent with the TC holder’s recommended procedures and training for operations in service. These procedures should address the recommended final approach airspeed, flare initiation height, thrust/power reduction height and technique, and target pitch attitudes.
8.2.5.2 At a height of 50 feet above the runway surface, the airplane should be at an airspeed no slower than the recommended final approach airspeed.
8.2.5.3 The touchdown rate of descent should be in the range of 1 to 4 feet per second.
Note: The criterion of paragraph 8.2.5.3 above should not be construed to mean that all of the landing data used to determine the air distance may have a touchdown rate of descent of 4 feet per second. The flight test data should contain a range of touchdown rates ranging from 1 to 4 feet per second.
8.2.6 The air distance determined under paragraph 8.2.4 or 8.2.5 of this AC also applies to autoland or similar low visibility guidance systems as long as the demonstrated average flare time and VTD/VAPP from the autoland testing do not exceed the values of those parameters used in determining the manual landing distance. If they do exceed the values used in determining the manual landing distance, then the demonstrated average flare time and VTD/VAPP from the autoland and/or low visibility guidance system demonstrations should be used for computing the air distance when determining the autoland and/or low visibility guidance system landing distance. The autoland/low visibility guidance system test data used for this determination should be from a representative set of airports and not include extreme glide path intercept points or runway slopes.
8.2.7 If the air distance is based on a time of 7 seconds at a speed of 98 percent of the recommended speed over the runway threshold, this air distance is considered valid for downhill runway slopes up to 1 percent in magnitude. (No credit should be taken for an uphill runway slope.)
8.3 Transition Distance.
8.3.1 As shown in figure 1, the transition distance is the distance traveled from the point of main gear touchdown to the point where all deceleration devices used in determining the landing distance are operating. For airplanes for which the air distance is determined using the guidance in paragraph 8.2.4 of this AC, the speed at the start of the transition segment is 96 percent of the final approach speed.
8.3.2 The transition distance should be based on the recommended procedures for use of the approved means of deceleration, both in terms of sequencing and any cues for initiation.
Reasonably expected time delays should also be taken into account.
8.3.3 For procedures that call for initiation of deceleration devices beginning at nose gear touchdown, the minimum time for each pilot action taken to deploy or activate a deceleration means should be the demonstrated time, but no less than one second.
8.3.4 For procedures that call for initiation of deceleration devices beginning prior to nose gear touchdown, the minimum time for each pilot action taken to deploy or activate a deceleration means should be the demonstrated time plus one second.
8.3.5 For deceleration means that are automatically deployed or activated (for example, auto-speedbrakes or autobrakes), the demonstrated time may be used with no added delay time.
8.3.6 The distance for the transition segment, and the speed at the start of the final stopping configuration segment should include the expected evolution of the braking force achieved over the transition distance. The evolution of the braking force should take into account any differences that may occur for different runway surface conditions or pilot-reported braking actions as the airplane transitions to the full braking configuration. (See table 2 of this AC for the wheel braking coefficient for the full braking configuration of each runway surface condition and pilot-reported braking action.)
Note: The wheel braking coefficients in table 2 of this AC were determined by the TALPA ARC part 25 working group, based on their experience and accepted performance levels on different surfaces as defined by aircraft certification agencies (EASA). They were verified to the greatest degree possible by the latest industry flight testing as embodied by the Joint Winter Runway Friction Program, which was active from 1995 to 2004. This AC may be revised if future industry-level acceptance of new information becomes available.
14 Table 2. Runway Surface Condition—Pilot-Reported Braking Action— Wheel Braking Coefficient Correlation Matrix Runway Condition Code Runway Surface Condition Description Pilot-Reported Braking Action Wheel Braking Coefficient 6 • Dry — 90% of certified value used to comply with § 25.1251.
5 • Frost
• Wet (includes damp and ⅛″ (3 mm) depth or less or water) ⅛″ (3 mm) depth or less of:
• Slush
• Dry snow
• Wet snow Good Per method defined in § 25.109(c).
4 -15 °C and colder outside air temperature:
• Compacted snow Good to Medium2
0.203 3 • Wet (“Slippery When Wet” runway)
• Dry snow or wet snow (any depth) over compacted snow Greater than ⅛″ (3 mm) depth of:
• Dry snow
• Wet snow Warmer than -15 °C outside air temperature:
• Compacted snow Medium2 0.163 2 Greater than ⅛″ (3 mm) depth of:
• Water
• Slush Medium2 to Poor
(1) For speeds below 85% of the hydroplaning speed4: 50% of the wheel braking coefficient determined in accordance with § 25.109(c), but no greater than
0.163; and
(2) For speeds at 85% of the hydroplaning speed4 and above:
0.053.
1 • Ice Poor 0.083 0 • Wet ice
• Water on top of compacted snow
• Dry snow or wet snow over ice Nil Not applicable. (No operations in Nil conditions.)
1 100% of the wheel braking coefficient used to comply with § 25.125 may be used if the testing from which that braking coefficient was derived was conducted on portions of runways containing operationally representative amounts of rubber contamination and paint stripes.
2 The braking action term “FAIR” is in the process of being changed to “MEDIUM” throughout the FAA. Until an official change is published, the term “FAIR” may be used.
3 These wheel braking coefficients assume a fully modulating anti-skid system. For quasi-modulating systems, multiply the listed braking coefficient by 0.625. For on-off systems, multiply the listed braking coefficient by 0.375.
(See AC 25-7C to determine the classification of an anti-skid system.) Airplanes without anti-skid systems will need to be addressed separately on a case-by-case basis.
4 The hydroplaning speed, VP, may be estimated by the equation VP = 9√𝑃, where VP is the ground speed in knots and P is the tire pressure in lb/in2.
8.4 Final Stopping Configuration Distance (Full Braking Distance).
8.4.1 As shown in figure 1, the final stopping configuration (full braking) segment begins at the end of the transition segment, which is the point where all deceleration devices used in determining the landing distance are operating. It ends at the nose gear position when the airplane comes to a stop.
8.4.2 The calculation of the final stopping configuration distance should be based on the braking coefficient associated with the runway surface condition or pilot-reported braking action, including the effect of hydroplaning, if applicable. Credit may be taken for the use of thrust reversers as described in section 10. See section 9 for information about taking into account contaminant drag from loose contaminants.
9 ACCOUNTING FOR DRAG OF LOOSE CONTAMINANTS.
9.1 Loose contaminants (see paragraph 7.1.1 of this AC for contaminant classification) result in additional contaminant drag due to the combination of displacement of the contaminant by the airplane tires and impingement of the contaminant spray on the airframe. This contaminant drag provides an additional force helping to decelerate the airplane, which reduces the distance needed to stop the airplane. Because contaminant drag increases with contaminant depth, the deeper the contaminant is, the shorter the stopping distance will be. However, the actual contaminant depth is likely to be less than the reported depth for the following reasons:
9.1.1 Contaminant depths are reported in field condition reports using specific depth increments as specified in FAA Order JO 7930.2Q (or later revision).
9.1.2 The procedure for reporting contaminant depths is to report the highest depth of the contaminant along the reported portion of the runway surface. Contaminant depths are unlikely to be uniform over the runway surface (or reported portion of the runway surface), so it is likely there will be areas of lesser contaminant depth.
9.1.3 In a stable weather environment (that is, no replenishment of the contaminant on the runway), the contaminant depth is likely to decrease as successive airplanes traverse through it and displace the contaminant.
9.2 If the actual contaminant depth is less than the reported value, using the reported value to determine contaminant drag will result in a higher drag level than actually exists, leading to an optimistic stopping distance prediction. Therefore, the FAA recommends not including the effect of contaminant drag in the calculation of landing distances for time-of-arrival landing performance assessments. If the effect of contaminant drag is included, it should be limited to no more than the drag resulting from 50 percent of the reported depth.
9.3 If the effect of contaminant depth is included in the landing distance data, then data should be provided for the reportable contaminant depths identified in FAA Order JO 7930.2Q (or later revision) up to the maximum contaminant depth for each contaminant for which landing operations are permitted.
Note: Due to issues of potential structural damage from spray impingement and engine ingestion, the maximum recommended depths for landing operations for loose contaminants of slush and water are ½ inch (13 mm) unless greater depths are demonstrated to be free of structural damage and engine ingestion issues.
9.4 If the effect of contaminant depth is included in the landing distance data, then data should be provided for the specific gravities in the table 3 below.
Table 3. Loose Contaminant Specific Gravity Runway Description Specific Gravity Dry Snow 0.2 Wet Snow 0.5 Slush 0.85 Water 1.0
9.5 The FAA finds acceptable the methods for calculating contaminant drag described in EASA AMC 25.1591. Data providers may also use a method that was previously accepted by EASA or has been validated by suitable analysis or test data.
10 CREDIT FOR REVERSE THRUST.
10.1 Landing distances used for time-of-arrival landing performance assessments may include credit for the stopping force provided by reverse thrust, consistent with the procedures established for its use and subject to meeting the following criteria:
10.1.1 Procedures used to calculate the landing distance should be consistent with normal procedures for use of reverse thrust during landing. The procedures should include all of the pilot actions necessary to obtain the recommended level of reverse thrust, maintain directional control and safe engine operating characteristics, and return the reverser(s), as applicable, to either the idle or the stowed position.
10.1.2 Using reverse thrust during a landing should comply with the engine operating characteristics requirements of § 25.939. The engine should not exhibit any of the adverse engine operating characteristics described in AC 25.939-1 (or later revision).
The reverse thrust procedures may specify a speed at which the reverse thrust is to be reduced to idle in order to maintain safe engine operating characteristics.
10.1.3 The time sequence for the actions necessary for the pilot to select the recommended level of reverse thrust should be achievable by the average pilot. If the procedure is to deploy reverse thrust at nose gear touchdown, the time for the first action to select reverse thrust may not be less than one second. If the procedure is to deploy reverse thrust before nose gear touchdown, the time for the first action to select reverse thrust should be the demonstrated time plus one second.
10.1.4 The response times of the affected airplane systems to pilot inputs should be taken into account. For example, delays in system operation, such as thrust reverser interlocks that prevent the pilot from applying reverse thrust until the reverser is deployed, should be taken into account. The effects of transient response characteristics, such as reverse thrust engine spin-up, should also be included.
10.1.5 To enable a pilot of average skill to consistently obtain the recommended level of reverse thrust under typical in-service conditions, a lever position that incorporates tactile feedback (for example, a detent or stop) should be provided. If tactile feedback is not provided, a conservative level of reverse thrust should be assumed.
10.1.6 If the data provider chooses to develop data using the process described in this AC, the effects of crosswinds on directional controllability should be assessed and particular attention paid to the possibility of reverse thrust affecting airflow over the rudder and vertical tail surface. Thrust reverser use may even reduce directional controllability in combinations of crosswinds and low friction conditions. Recommendations or guidelines associated with crosswind landings, including maximum recommended crosswinds, should be provided to operators for the runway surface conditions/reported braking actions for which landing distance data are provided. A suitable simulation may be used to develop these guidelines for operation on contaminated runways.
10.1.7 If the data provider, in using the process described in this AC, applies credit for less than all thrust reversers, then controllability should be accounted for in that configuration. The reverse thrust procedures may specify a speed at which the reverse thrust is reduced to idle in order to maintain directional controllability.
10.1.8 The failure of the thrust reverser to function should be on the order of 10-4 or less per landing. This specific reliability requirement applies to both single and combinations of failures and takes into account interlock features intended to prevent inadvertent in-flight deployment.
10.1.9 For dispatch with one or more inoperative thrust reverser(s), or for an in-flight failure that affects thrust reverser operation, the effect on the landing performance data for time-of-arrival landing performance assessments should be provided.
10.1.10 The effective stopping force provided by reverse thrust in each, or at the option of the data provider, the most critical landing configuration, should be accounted for by flight test. (One method of determining the reverse thrust stopping force would be to compare unbraked runs with and without the use of thrust reversers.) Regardless of the method used to calculate the effective stopping force provided by reverse thrust, flight tests
18 should be conducted using all of the stopping means on which the landing distances are based in order to calculate the landing distances and ensure that no adverse combination effects are overlooked. These tests may be conducted on a dry runway.
10.2 For turbopropeller powered airplanes, the guidance in paragraphs 10.1 through 10.1.10 above remains generally applicable. Additionally, the propeller of the inoperative engine should be in the position it would normally assume when an engine fails and the power lever is closed. Reverse thrust may be selected on the remaining engine(s).
Unless this selection is achieved by a single action to retard the power lever(s) from the takeoff setting without encountering a stop or lockout, it should be regarded as an additional pilot action for the purposes of assessing delay times.
11 GUIDANCE FOR EXISTING TYPE DESIGNS.
The guidance in this section applies to data already produced to support airplane models already in service.
11.1 The following information is intended to facilitate the use of existing data to the maximum extent possible, in order to limit the burden associated with developing and producing new data packages.
11.2 The data may be presented in terms of runway surface conditions, pilot-reported braking actions, or both.
11.2.1 If data are provided in terms of only one of these parameters, instructions should be provided on how to use the data in terms of the other parameter. For example, when data are provided only in terms of pilot-reported braking actions, instructions should be provided on how to use the data to perform a time-of-arrival landing performance assessment in terms of a runway surface condition description.
11.2.2 Table 2 of this AC can be used to relate runway surface condition descriptions to reported braking actions. If data providers have landing performance data in terms of runway surface condition descriptions and credit is taken for drag from loose contaminants, there will not be a one-to-one correspondence between runway surface condition descriptions and pilot-reported braking actions.4 In this case, a conservative correction should be applied to the data to remove the effect of contaminant drag. For example, using data based on greater than ⅛-inch depth of water or slush for a pilot-reported braking action of medium to poor.
11.3 Contaminated runway landing performance data approved by either the Joint Aviation Authorities or EASA in compliance with either their contaminated runway type
4 Pilot-reported braking actions consider only the friction effects of the contaminants on wheel braking and directional controllability and, therefore, will not include the effects of any contaminant drag.
19 certification or operating requirements are acceptable when using the optional process identified in this AC, with the following caveats:
11.3.1 The data provider should develop data that accounts for all of the runway surface condition descriptions identified in table 2 of this AC (unless operating limitations prohibit operations on runway surface conditions for which data are not provided).
11.3.2 The effects of runway slope, temperature, and speed over the threshold should be included.
11.3.3 Definitions of the runway surface conditions should be consistent with the definitions provided in this AC. In particular, a damp runway is to be considered wet for airplane performance purposes.
11.3.4 It is recognized that such data may not conform to the guidance provided in this AC in terms of air distance, transition time assumptions, use of deceleration devices, braking coefficients associated with each runway surface condition description, and the amount of contaminant drag for loose contaminants.
11.4 Reverse thrust credit may be included without specifically accounting for reliability or controllability. However, reverse thrust credit should not be used if service history for a particular airplane model indicates unresolved reliability or controllability issues.
12 DOCUMENTATION.
12.1 Data Location.
The data provider may furnish the time-of-arrival landing performance data in the airplane flight manual, flightcrew operating manual, quick reference handbook, electronic flight bag, and/or other appropriate locations.
12.2 Data Label.
Wherever the data is provided, label the data as “Advisory Data Only” or use similar wording.
12.3 Other Information.
If a data provider develops the landing performance data described in this AC, the following information should also be provided:
12.3.1 Instructions for use.
12.3.2 Definitions of runway surface condition and how to correlate runway surface condition descriptions, runway condition codes, and braking actions.
12.3.3 Recommendations prohibiting landing on runways with contaminants and depths beyond those covered in the performance data.
12.3.4 Any other recommendation associated with use of the landing performance data.
12.3.5 Statements that the data are based on a uniform depth (for loose contaminants) and uniform coverage of a layer of contaminant with uniform properties throughout.
12.3.6 The procedures and assumptions used to develop the operational landing distances.
Advisory Circular Feedback If you find an error in this AC, have recommendations for improving it, or have suggestions for new items/subjects to be added, you may let us know by (1) emailing this form to 9-AWA-AVS- AIR500-Coord@faa.gov or (2) faxing it to the attention of the Aircraft Certification Service Directives Management Officer at (202) 267-3983.
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