15.1.2.4 Position indication and aural warning, § 25.729(e): It should be confirmed that the actual landing gear position agrees with the position indicated on the landing gear indicator. Landing gear aural warning should meet the intent of § 25.729(e)(2) through (e)(4). A combination of flight tests, ground tests, and analysis may be used to show compliance with these requirements.
15.2 Wheels—§ 25.731.
15.2.1 References.
TSO-C135a, Transport Airplane Wheels and Wheel and Brake Assemblies, dated July 1, 2009.
Paragraph 15.4.2.5 of this AC, Wheel Fuse Plugs.
Paragraph 15.4.10 of this AC, Wheel Fuse Plug Integrity.
AC 21-29D.
15.2.2 Explanation.
15.2.2.1 Original guidelines for wheels in § 4b.335 of the Civil Air Regulations (CAR) were superseded by TSO-C26 and subsequent revisions. Early versions of TSO-C26 referred to minimum standard requirements in versions of Society of Automotive Engineers (SAE) Aeronautical Standard (AS) 227. Minimum standards were subsequently specified in TSO-C26b and later revisions. For braked wheels, wheels and brakes must be approved under § 25.735(a) as an assembly in recognition of design and safety interdependencies associated with thermal control, vibration control, structural stresses, etc. Paragraphs 15.4.2.5 and 15.4.10 of this AC provide insight into the criticality of proper fuse function to support airworthiness. As demands increased for longer life wheels and more robust designs, changes were introduced such as the addition of combined vertical and side loads for a portion of roll testing; an increase in roll miles at maximum static load from 1,000 to 2,000 miles; and addition of a rollon-rim requirement to increase robustness in wheel flange areas.
15.2.2.2 In most cases, wheels are usually removed from service based upon condition. Typically, inspection frequency will increase as life on a particular wheel is accumulated in accordance with the wheel and brake supplier’s component maintenance manual (CMM). If wheel failures occur on the airplane, they typically occur when the airplane is on the ground with wheel and tire assembly loaded.
15.2.2.3 The trend in certain airplane manufacturer specifications is to place additional longevity and safety focused test requirements on wheel and brake suppliers. Added requirements, such as fail-safe design 15-2
verification(s), testing to failure of uncorroded and corroded wheels, and mandated use of over pressurization protection devices (in addition to fuses) have been incorporated. With the introduction of longer life tires, the demands on wheels and components, such as wheel bearings, have further intensified as landings between inspections at tire overhauls have increased. In addition, airplane manufacturers should be involved in wheel design, test, and manufacturer approvals to ensure that airplane specific needs have been addressed. For example, at least one airplane manufacturer specifies a missing wheel tie bolt requirement so that minimum equipment list (MEL) dispatch relief can be provided for a limited number of cycles. As a second example, individual airplane manufacturers may specify intensified wheel load and/or test requirements to account for various tire failure modes on multi-wheeled landing gear truck and other airplane landing gear configurations. Therefore, continued airworthiness of a particular wheel/tire or wheel/brake/tire assembly is usually demonstrated by compliance with airplane manufacturer requirements and not TSO minimum standards.
15.2.2.4 Separate wheel applicable TSO and (if applicable) airplane manufacturer tests are performed with radial and bias tires due to different tire-to-wheel interface loading and resultant wheel stress pattern and deflection/clearance differences. For braked wheels, separate wheel and brake assembly tests are performed with radial and bias tires due to differences in tire energy absorption that may be encountered. Some significant differences in wheel life have been reported by one wheel and brake supplier in one case using bias tires from different tire manufacturers. Typically, however, wheel/tire, or wheel/brake/tire assembly tests using different manufacturer bias tires have not been shown to be necessary.
15.2.2.5 Wheel bearings in transport category airplane wheels should be qualified as part of the wheel assembly. Industry experience indicates that qualification of a specific manufacturer’s bearing(s) in a given wheel assembly is required to assure proper performance and airworthiness.
Standard part bearing assemblies are not acceptable unless performance can be demonstrated during wheel qualification testing. It has been reported that roller end scoring is the most common mechanism leading to bearing failures on the airplane.
15.2.2.6 Improved wheel bearing grease and bearing preload retention means have also been introduced on some recent airplanes to increase wheel bearing longevity in the severe landing gear system environments and account for longer tire lives/ increased intervals between tire changes and inspections.
Bearing wheel grease recommendations are usually specified in wheel and brake supplier CMMs. Intermixing of bearing cups/rollers/cones from different bearing manufacturers is not recommended on some large 15-3
transport category airplane wheels due to different roller end scoring resistance capabilities and other often subtle differences.
15.2.3 Procedures/Method of Compliance.
Due to the unique and critical nature of wheel, and wheel and brake designs, and historical airplane and personnel safety problems that have been experienced, compliance should only be approved upon successful completion of all applicable tests.
We recommend guidance be solicited from the original wheel and brake supplier(s)
(e.g., technical standard order authorization (TSOA) or letter of design approval (LODA) holder) on any replacement part(s) to assure that continued airworthiness is not degraded.
15.3 Tires—§ 25.733.
[Reserved]
15.4 Brakes—§ 25.735.
15.4.1 References.
TSO-C135a, Transport Airplane Wheels and Wheel and Brake Assemblies, dated July 1, 2009.
AC 25-22.
AC 25.735-1.
15.4.2 Explanation.
15.4.2.1 Background.
15.4.2.1.1 The original objective of § 25.735 (formerly § 4b.337) developed from a study to define a reasonable brake life for operational landings. This element is still retained in current § 25.735(f)(1), which requires substantiation that the wheel, brake, and tire assembly have the ability to absorb the energy resulting from an operational landing stop at maximum landing weight. Compliance with this requirement is shown through dynamometer testing.
15.4.2.1.2 It later became evident that a rejected takeoff could be critical in determining overall brake capability, and the maximum RTO energy absorption capability by the brakes could limit the aircraft maximum allowable gross weight for dispatch.
15.4.2.1.3 Investigation of an RTO overrun accident, in which 80 percent of the brakes on the subject airplane were at or very near their completely worn state, brought about the need to consider the effect of brake wear state on energy absorption capability, and stopping capability. As a result, the FAA 15-4
issued a series of specific airworthiness directives for the existing fleet of transport category airplanes to establish brake wear limits such that the brakes would be capable of absorbing a maximum energy absorption RTO in the fully worn state. The FAA also initiated rulemaking to address energy absorption capability and stopping distance with fully worn brake for future airplane types. The resulting rule, amendment 25-92, added:
1. A requirement for the maximum rejected takeoff kinetic energy capacity rating of the aircraft brakes to be determined with the brakes at 100 percent of the allowable wear limit;
2. A new requirement for the maximum kinetic energy rejected takeoff flight test demonstration to be conducted using brakes that have not more than 10 percent of their allowable wear range remaining; and
3. A general performance requirement under § 25.101(i) that requires the accelerate-stop and landing distances of §§ 25.109 and 25.125, respectively, to be determined with all wheel brake assemblies at the fully worn limit of their allowable wear range.
15.4.2.1.4 ACs 25-22 and 25.735-1 provide guidance and policy on how to show compliance with § 25.735. Additional information is provided in the following paragraphs pertaining to flight test evaluations performed in connection with showing compliance.
15.4.2.2 Brake Controls—§ 25.735(c).
General brake control force and operation should be noted throughout the flight test program to determine that they are satisfactory.
15.4.2.3 Brake Control Valves.
The brake valves in the normal brake system should allow the pilots to modulate pressure to the brakes. The foregoing provision need not necessarily apply to an alternate or emergency brake system, although obviously such a provision would be desirable. Flight tests should be conducted to determine that the normal and alternate/emergency brake systems fulfill the requirements of § 25.231.
15.4.2.4 Parking Brake—§ 25.735(d).
A demonstration should be made to determine that sufficient braking is provided with the parking brake to prevent the airplane from rolling on a paved, dry, level runway (or any suitable level hard surface) while maximum takeoff power or thrust is applied on the most critical engine and up to maximum ground idle power or thrust is applied to all other engines. The airplane should be loaded to the maximum ramp weight at aft CG (or a weight-CG combination that prevents the wheels from sliding).
In the case of propeller-driven airplanes, the effects of propeller wash and engine/propeller torque should also be considered in determining the critical engine. Because the resultant thrust vector can be at an angle to a 15-5
propeller’s axis of rotation, one engine/propeller may be more critical than its counterpart on the opposite wing, particularly if all propellers turn in the same direction.
15.4.2.5 Wheel Fuse Plugs.
15.4.2.5.1 The hazardous condition of exploding tires and wheels associated with high energy emergency stopping conditions has been greatly alleviated by the installation of wheel fuse plugs. These plugs relieve the tire pressure when the wheel temperatures approach a dangerous limit. The effectiveness of these plugs in preventing hazardous tire blowouts should be demonstrated during an RTO test where the brake energy to be absorbed exceeds the maximum landing energy, but not the RTO energy, and the fuse plug releases, thereby deflating the tire(s) before blowout.
15.4.2.5.2 An improperly designed blowout plug that allows premature or unwanted release of tire pressure during takeoff or landing could also constitute a hazardous condition. Such a situation would most probably arise during a takeoff from a quick turn-around type of airline operation. Fuse plug integrity should be demonstrated by conducting a maximum landing brake energy test, which should not result in a fuse plug release.
15.4.2.5.3 Most turbojet transport airplanes have been able to demonstrate wheel blowout plug integrity at a maximum energy level in accordance with the procedures outlined in this section. More restrictive operational limitations
(e.g., runway slope and tailwind values) have been imposed to stay within this maximum energy level demonstrated for wheel blowout plug integrity. With the advent of requests to increase the maximum landing weights, and to eliminate these restrictive operational limits, it has been considered acceptable to remove the pertinent restrictions and operational limitations and substitute in their place a chase-around chart as a limitation in the AFM. This chart will permit determining whether or not a critical energy level has been exceeded for the operating conditions of altitude, temperature, runway slope, tailwind, and landing weight. When the critical value is exceeded, a statement should be placed in the limitations section of the AFM to require that following a landing under such operating conditions, the airplane must remain on the ground a certain length of time prior to taxiing out for takeoff. This length of time will be the time to reach peak wheel temperatures (appropriate to the blowout plug location), plus 15 minutes. In lieu of the AFM fuse plug limitation chart, an alternate method for determining limit operational landing energy, such as a brake temperature limit, can be considered for approval.
15.4.2.5.4 The wear level of the brakes used for the chase-around chart discussed in the preceding paragraph should be selected by the applicant. Service experience indicates that the conservatism contained in the method of 15-6
determining the turnaround time limits is adequate to allow these limits to be determined using new brakes.
15.4.2.5.5 In the case where it is possible to demonstrate wheel blowout plug integrity at a maximum energy level in accordance with the procedures in this section and without imposing certain restrictions on the operational limitations (e.g., runway slope and tailwind values), it is not considered necessary to incorporate the chase-around chart and pertinent statement in the limitations section of the AFM. Where restrictions are necessary, a pertinent statement and reference to the chase-around chart could be included in the limitations section of the AFM.
15.4.2.6 Replacement and Modified Brakes.
15.4.2.6.1 In order to establish aircraft landing and RTO certification performance levels for a replacement brake or a modified brake, measured acceleratestop tests, and functional flight tests (landing distance), may be required, depending upon an evaluation of the individual merits of each brake system change. The type and magnitude of flight tests required will depend on whether or not a requested change involves a corresponding change of heat sink and/or torque requirements of the original certificated brake. A review of the change by the cognizant aircraft certification office (ACO) for the type certificate holder is necessary, since original landing gear designs are based on structural analysis, which could be adversely affected by a brake system change. In addition, such tests will also depend on whether or not an improvement in the FAA certificated performance is desired by the applicant.
15.4.2.6.2 Changes to the friction couple elements (rotors and stators) are generally considered to be a major change, requiring the testing described in paragraph 15.4.4, unless it can be shown that the change cannot affect the airplane stopping performance, brake energy absorption characteristics, or continued airworthiness. Historically, continued airworthiness considerations include such items as landing gear system/airplane vibration control, braking feel, landing gear system compatibilities etc.
15.4.2.6.3 Changes to a brake by a manufacturer other than the original TSO holder might be considered to be a minor change, as long as the changes are not to the friction couple elements, and the proposed change(s) cannot affect the airplane stopping performance, brake energy absorption, vibration, and/or thermal control characteristics, and continued airworthiness of the airplane. In certain circumstances, the change to a steel rotor by a manufacturer other than the original TSO holder may be considered to be a minor change, as discussed in paragraph 15.4.8.2.
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15.4.3 Procedures.
The extent of the flight test requirements, except new airplane certification, may vary depending upon an evaluation of the individual merits of each airplane brake system change, and whether an increase in the FAA certificated performance level is desired by the applicant. Past experience has proven that dynamometer tests alone are not considered adequate in determining compliance with this requirement. Flight test procedures for new, replacement, and modified brakes are categorized as follows:
15.4.4 New Airplane Certification.
This is a completely new design where no airplane performance data exist.
15.4.4.1 Required Tests.
15.4.4.1.1 For complete analysis, at least six rejected takeoffs and six landings will normally be necessary.
1. Landings should be conducted on the same wheels, tires, and brakes.
2. All tests should be conducted with engines trimmed to the high side of the normal idle range (if applicable).
3. For airplanes whose certification basis includes amendment 25-92, § 25.101(i) requires the stopping distance portions of the accelerate-stop and landing distances to be determined with all the aircraft brake assemblies in the fully worn state. An acceptable means of compliance with this requirement is to accomplish the flight test braking tests with less than fully worn brakes, and then correct the test results using dynamometer test data determined with fully worn brakes. It should be substantiated that the dynamometer test methodology employed, and analytical modeling of the airplane/runway system, are representative of actual conditions.
15.4.4.1.2 Additional tests may be necessary for each airplane configuration change
(i.e., takeoff and/or landing flaps, nose wheel brakes, anti-skid devices inoperative, deactivation of wheel brakes, etc.).
15.4.4.1.3 Brake system response evaluation including braking during taxiing (see paragraph 9.2.2.1.)
15.4.4.1.4 Parking brake adequacy. (See paragraph 15.4.4.3.)
15.4.4.1.5 Alternate braking system stops.
15.4.4.1.6 Wheel fuse plug evaluation. (See paragraph 15.4.10.)
15.4.4.1.7 Anti-skid compatibility on a wet runway.
15.4.4.1.8 Automatic gear retraction braking system on airplanes so equipped.
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15.4.4.2 Maximum RTO energy will be established by conducting an RTO at the maximum brake energy level for which the airplane will be certified. Fires on or around the landing gear are acceptable if the fires can be allowed to burn during the first 5 minutes after the airplane comes to a stop, before extinguishers are required to maintain the safety of the airplane. The condition of the tires, wheels, and brakes can be such that the airplane would require maintenance prior to removal from the runway. A deceleration rate should be maintained during this test that is consistent with the values used by performance scheduling. Tire or wheel explosions are not acceptable. Tire fuse plug releases may occur late in the RTO run, provided directional control is not compromised. The resulting distance (with fuse plugs blown during the RTO run) is to be included in the data used to establish AFM performance, only if it is longer than the data obtained with normal full braking configuration.
15.4.4.2.1 For airplanes whose certification basis includes amendment 25-92, the maximum brake energy absorption level must be determined, according to § 25.101(i), for an airplane with all wheel brake assemblies in the fully worn state. In accordance with § 25.109(i), the flight test maximum energy RTO demonstration must be accomplished with all brake assemblies within 10 percent of their allowable wear limit (i.e., at least 90 percent worn). Dynamometer testing, when used to extend the flight test results to determine the maximum energy absorption capability of the brakes in the fully worn state (i.e., 100 percent worn), should be substantiated as being representative of actual airplane and runway conditions. The fully worn limit is defined as the amount of wear allowed before the brake needs 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.
15.4.4.2.2 The maximum energy RTO demonstration should be preceded by at least a three-mile taxi, with at least three intermediate full stops, using normal braking and with all engines operating.
15.4.4.2.3 Landings are not an acceptable means to conduct maximum energy RTO demonstrations. 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 were not able to account accurately for the associated energy increments.
15.4.4.3 The ability of the parking brake to prevent the airplane from rolling should be demonstrated on a paved, dry, level runway (or any suitable level hard surface) with takeoff power or thrust applied on the critical engine and up to maximum ground idle power or thrust is applied to all other engines using the following test procedure:
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15.4.4.3.1 The airplane should be loaded to its maximum takeoff weight (or a weight-CG combination that prevents the wheels from sliding) with the tires inflated to the normal pressure for that weight, the flaps should be retracted, the control surfaces centered, and the parking brake set.
15.4.4.3.2 Apply takeoff power or thrust to the critical engine with the other engine(s) at maximum ground idle power or thrust.
15.4.4.3.3 Compliance with the requirements of § 25.735(d) is shown if the wheels do not rotate; this is best observed by painting a white radial stripe(s) on the wheels. The airplane may skip, tire tread may shear, or the tire may slip on the wheel, but the parking brake must prevent the wheels from rotating. Skidding of the tires is acceptable.
15.4.5 Addition of New or Modified Brake Design.
15.4.5.1 This item concerns the addition of a new or highly modified brake design to an existing type-certificated airplane for which FAA-approved braking performance test data exists, either for performance credit, or to the existing performance level. A highly modified brake is defined as one that contains new or modified parts that may cause a significant variance in brake kinetic energy absorption characteristics, airplane stopping performance, or continued airworthiness of the airplane. Examples are:
significant change in rotor and/or stator lining compound or area, number of stages, piston area, reduction in heat sink weight, changes in total number of friction faces and elements, change in brake geometry (friction, radius, friction area), fuse plug relocation or change in release temperature, heat shield changes that would affect the temperature profile of the wheel and/or fuse plugs, or seal changes.
15.4.5.2 Required Tests.
15.4.5.2.1 For improved performance, all applicable portions of paragraph 15.4.4.
15.4.5.2.2 For equivalent performance, a sufficient number of conditions to verify the existing approved performance levels (RTO and landing).
Consideration should be given to verification of fuse plugs, performance verification at appropriate energy levels, and configuration differences, including antis-kid on and off. Taxi tests to ensure that ground handling, maneuvering, and brake sensitivity are satisfactory should be conducted.
At least two braking stops, one at heavy weight and one at light weight, should be conducted on a wet runway to verify brake and anti-skid system compatibility.
15.4.5.2.3 For extended performance, a sufficient number of conditions to define the extended line and determine equivalency to the existing performance levels. Consideration should be given to the items in paragraph 15.4.5.2.2 above.
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15.4.5.3 Definitions.
15.4.5.3.1 Improved performance implies an increase in the mu versus energy level for the desired operation(s) and may be requested for landing, RTOs, or a specific configuration such as anti-skid “on” only.
15.4.5.3.2 Equivalent performance implies that sufficient data will be obtained to verify that the performance level for the desired change is equal to or better than the existing performance levels. The change may be for the purpose of changing the CG envelope, or for airplane configuration changes (such as flap angles) and may apply to specific operations (such as landings).
15.4.5.3.3 Extended performance implies that the existing certification mu versus energy line will be extended to establish the braking force level for a proposed change, such as gross weight or the maximum desired energy level and may be applied to a specific operation (such as landing only).
15.4.6 Addition of New, or Changes to, Anti-skid Systems that may Affect Airplane Performance.
(For example, new anti-skid system, or a change from coupled to individual wheel control.) A sufficient number of airplane performance tests and/or functional tests should be conducted to verify existing approved performance anti-skid “on” levels. In the event an increase of braking performance is desired, full airplane performance testing is required.
15.4.7 Fuse Plug Modification.
15.4.7.1 Airplane tests for changes to the fuse plugs should be evaluated on a case-by-case basis. While airplane tests are required to establish the initial fuse-plug-no-melt energy, minor changes to fuse plugs or wheel designs may be validated by a back-to-back dynamometer comparison of old versus new designs, provided it is acceptable to the cognizant FAA ACO.
15.4.7.2 Airplane tests should be conducted when a significant change of wheel design and/or redesign or relocation of thermal or pressure fuse plugs is made. One airplane test should be conducted to show that the fuse plugs will release when excessive energies are absorbed. Another airplane test should be conducted to verify the maximum kinetic energy at which fuse plugs will not release (fuse plug substantiation). Dynamometer tests are not considered adequate for this test.
15.4.8 Minor/Major Changes.
15.4.8.1 Minor brake changes that do not affect airplane braking performance may require functional landings. This may be required to verify airplane-pilot-brake-anti-skid combination compatibility. Normally, five 15-11
non-instrumented, functional landings are considered sufficient to verify this compatibility. Examples of minor changes might include structural improvements (increased fatigue life), adjuster/retractor modifications, material and process specifications changes for structural components, and modified heat-sink relief slots (steel brakes). Examples of other minor changes that do not require functional landings are paint/corrosion changes, changes to bleed ports or lube fittings, revised over inflation devices, metal repair, and salvage procedure.
15.4.8.2 Changes to heat sink friction couple elements are to be considered major changes, unless the applicant can provide evidence that changes are minor.
Based upon experience, thicker friction material or heavier heatsink elements are usually acceptable as minor changes in steel brakes. Thicker or heavier heat sink elements in carbon brakes may require additional laboratory and/or airplane testing to assess brake performances and continued airworthiness. Major changes are subject to extensive airplane testing, unless it can be shown that the change cannot affect the airplane stopping performance, brake energy absorption characteristics, and continued airworthiness. In this regard, the original manufacturer of the wheel/brake assembly, who holds the TSO authorization and the type certificate holder, who is knowledgeable with respect to such items as landing gear design assumptions and airplane braking system history, may possess data sufficient to show that such changes could be considered to be minor (i.e., performance would not be affected). In contrast, an applicant other than the original manufacturer who wishes to produce replacement rotors or stators may not have access to or have established developmental or other test data required to show that performance, braking energy capacities, braking system compatibilities, or overall continued airworthiness safeguards have been addressed. Due to the complex nature of the friction surfaces and airplane braking system interfaces, proposed replacement stators/rotors by an applicant other than the original manufacturer(s) should always be considered a major change.
15.4.8.3 It is considered very difficult to determine 100 percent identicality. This is particularly true for brake friction rubbing components (e.g., linings in cups, linings sintered to plates, steels used in steel brakes, and carbon discs in carbon brakes). A finding of equivalence based upon physical documentation and dynamometer testing may not be possible or practical due to friction material complexities and/or the extent of dynamometer testing required.
15.4.8.4 Due to the complexities associated with aircraft brake friction couples, industry and authorities have generally discouraged mixing of friction components from various suppliers within the same brake or mixing wheel and brake assemblies from different manufacturers on the same airplane.
Typically, the manufacturers of large transport category airplanes have confined the use of specific wheel and brake supplier’s assemblies to 15-12
specific airplanes through approved equipment lists. While multiple wheel and brake suppliers (e.g., multiple original TSO holders) are often selected to provide wheel and brake assemblies on a specific airplane model, intermixing of wheel and brake assemblies has been discouraged to avoid potential problems such as unequal energy sharing; unfavorable dynamic cross coupling between brakes, landing gear, and the airplane; degradation of vibration and/or thermal controls; unique brake control system tuning requirements for each wheel and brake assembly, etc.
15.4.8.5 The FAA has, however, approved the use of replacement steel rotors. The following protocol for steel rotor equivalency findings has been updated to include brake wear and wear pattern assessments to assure that the worn brake capability of the original manufacturer’s wheel and brake assembly is not degraded by a replacement steel rotor(s). The following criteria and evaluations represent protocol for replacement steel rotors to be considered as a minor change:
1. A very close correlation between the original part and the proposed replacement part;
2. Considerable and satisfactory prior manufacturing and in-service experience with a similar replacement part;
3. A reasonable plan of test for completion of the dynamometer portion of the test program;
4. Successful completion of the dynamometer testing; and
5. As a minimum, successful completion of a series of functional landings on the airplane.
15.4.8.6 The necessity of conducting maximum energy RTO testing and other brake system tests on the airplane will depend upon the outcome of the above evaluations and worn brake RTO airplane test experiences (if applicable).
15.4.8.7 If intermixing of replacement steel rotors with the original manufacturer’s steel rotors is proposed, the applicant should propose an airplane test evaluation plan to the FAA that provides data to guide a worn brake rejected-takeoff equivalency assessment. If the applicant cannot provide evidence on similar overall wear and wear patterns from the new to worn condition for the proposed mixing configuration(s), intermixing will not be permitted in order to assure that the worn brake rejected-takeoff rating and approved wear limit of the original TSO holders wheel and brake assembly is not jeopardized.
15.4.8.8 The dynamometer test plan, and, if applicable, the overall wear and wear pattern test plan, should include:
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