65 Part 23, § 23.1301 (3.652) Func tion and installations Part 23, § 23.1309 Equipment, sy stems, and installations Part 23, Appendix D Wheel spin-up and spring back loads
Part 23, § 23.1529 and Instructions for Continued Airworthiness Appendix G to Part 23
Part 135, Appendix A Additional airworthiness standards for 10 or more passenger airplanes
Part 45, § 45.14 Identificatio n of critical components
Part 45, § 45.15 Replacement and modification parts
b. Advisory Circulars (AC's) AC 23-8C “Flight Test Guide for Certification of Part 23 Airplanes.”
c. Technical Standard Order (TSO) TSO-C26d “Aircraft Wheels, Brakes and Wheel/Brake Assemblies for Parts 23, 27 and 29 Aircraft, with Addendum 1,” October 14, 2004.
d. Industry Documents SAE ARP 597D “Wheels and Brak es, Supplementary Criteria for Design for Endurance-Civil Transport Aircraft,” February 7, 2008.
SAE ARP 813B “Maintainability Recommendations for Aircraft Wheels and Brake Design,” February 1, 1995.
SAE AIR 1064D “Braking System Dynamics,” September 26, 2007.
SAE AS 1145B “Aircraft Brake Temperature Monitor System (BTMS),” February 1, 1998.
SAE ARP 1619A “Replacement and Modified Brakes and Wheels,” March 1, 2001.
2. Background
A review of recent replacement and modification wheel/brake system and installation approvals on part 23 airplanes has resulted in the need to provide FAA guidelines that clearly describe the changes and associated substantiation procedures involved. As contained herein, these guidelines will reflect on issues that have been identified by industry under ARP 1619A, which, in part, concerns the variance in compliance provisions associated with original equipment manufacturers (OEM) and non-OEM applicants. The guidelines will include: 1) a description of replacement or modified wheel, 2) wheel/brake parts or assembly changes, 3) a description and examples of associated "major" and "minor" changes, and 4) a description of corresponding laboratory and airplane flight tests needed to ensure that requested changes will result in a continued level of airplane safety and performance.
3. Classification of replacement and Modified Wheel/Brake Changes
a. Replacement of Wheel, Wheel/Brake Parts, or Assembly Changes
A replacement wheel, wheel/brake part, or an assembly change is classified as one in which either the included parts or assemblies that are being changed are of equivalent design. This will result in an equivalent level of certified type performance and safety to that shown by either the originally approved parts or assemblies. The change may be approved under a PMA by the provisions of part 21. Under part 21, § 21.303, an applicant may be eligible for approval of either PMA replacement parts or assemblies, or both, by showing compliance in accordance with the following methods, as applicable:
(1) Licensing Agreement
Applicant should provide evidence of a licensing agreement or equivalent with the holder of a TSOA, TC, or an STC with the submission of any design data covered by the licensing agreement, as determined by the FAA. See Order 8120.2G for procedure.
(2) Identicality
Applicant should provide evidence the parts he produces will be identical to the corresponding parts of an approved 14 CFR type design, TSO, or PMA. Data submitted should include all applicable design, material, and process specifications that is, technical data that would specify all dimensions, tolerances, materials, processes, and specifications to the design of the corresponding part of an approved design.
(3) Airworthiness Requirements (Tests and Analyses)
Applicant should provide evidence in the form of drawings, test reports, computations, and other substantiating data showing the part meets either the applicable part 23 airworthiness requirements or the certification basis under which the airplane was approved (see the following NOTE). See Order 8110.42C.
Compliance to applicable part 23 airworthiness requirements may include:
(a) Part 23, § 23.55 and Accelerate-stop distance for Part 135, Appendix A commuter cat egory airplanes and other airplanes that have accelerate-stop distance requirements, includi ng airplanes that have published data such as stopping distances and brake energy/cooling charts in the AFM.
(b) Part 23, § 23.75 Landing.
(c) Part 23, § 23.143 Controllabi lity and maneuverability:
General.
(d) Part 23, § 23.231 Longitudinal stability and control.
(e) Part 23, § 23.233 Directional stability and control.
(f) Part 23, § 23.493 Braked roll conditions.
(g) Part 23, § 23.731 Wheels.
(h) Part 23, § 23.735 Brakes.
(i) Part 23, § 23.1301 Func tion and installation.
(j) Part 23, § 23.1309 Equipment, systems, and installations.
(k) Part 23, § 23.1529 and Instru ctions for Continued Appendix G to Part 23 Airworthiness.
(l) TSO-C26d “Aircraft Wheels, Brakes and Wheel/Brake Assemblies for Parts 23, 27 and 29 Aircraft with Addendum 1,” October 14, 2004.
NOTE: A description of the certification basis in which an airplane was approved can be obtained from the FAA.
Change 1 AC 23-17C 7/16/2012
b. Identical Wheel, Wheel/Brake Parts, or Assembly
An identical wheel, wheel/brake part, or assembly is classified as a replacement in which either the included parts or assemblies being changed are of an identical design and will result in an equivalent level of demonstrated performance to that shown by either the originally approved parts or assemblies.
c. Modified Wheel, Wheel/Brake Parts, or Assemblies May Be Approved Under a Provision of Part 21 Under part 21, § 21.303, an applicant may be eligible for approval of modified wheel, wheel/brake parts, or assemblies by showing compliance to methods identified under paragraph 3.a.(3) above “Airworthiness Requirements (Tests and Analysis)”. If modified wheel, wheel/brake parts, or assemblies are not produced for sale, then § 21.8 is applicable.
d. Major Wheel, Wheel/Brake Parts, or Assembly Changes Since design changes appropriate to replacement and modified wheels, wheel/brake parts, or assemblies may involve changes to the original TSO wheel or wheel/brake assembly approval basis under an STC or TC in which the wheel or wheel/brake was installed, the applicant should also comply with applicable provisions for "major" design changes under part 21, § 21.93.
4. Substantiation Procedures
Replacement and modified wheels, wheel/brake parts or assembly changes should be substantiated by conducting the necessary analytical investigations, laboratory testing, or airplane testing, or all of these, to ensure the change can be made without adversely affecting aircraft safety and associated braking and rolling performance. A substantiation plan should first be proposed by the applicant for FAA approval followed by the applicant's implementation of the plan.
a. Substantiation Plan
A proposed substantiation plan may be presented to the FAA for approval that identifies the applicants requested change and intended approach in substantiating the change in accordance with the methods addressed under this section. The plan should include:
(1) A description of the replacement or modified part or assembly, or both.
(2) An assessment covering the applicable airworthiness requirements involved.
(3) A statement of change that is determined to be either "major" or "minor" and the basis for the classification about the applicable requirements of part 21.93.
(4) An assembly drawing reflecting the replacem ent or modified part or assembly, or both.
(5) Aircraft installation drawings/instructions.
(6) The substantiation method, which in cludes an analysis/test protocol.
(7) The method of identification and maintenance procedures that will be used.
(8) The quality management and quality a ssurance system under which either the part or assembly, or both, will be produced.
b. Substantiation Requirements The recommended substantiation requirements for replacement and modified wheels, wheel/brake parts or assemblies are based on changes for which approval is sought, and the impact a new part or assembly will have on prior certification. If the replacement and modified wheel, wheel/brake part or assembly meets the minimum applicable airworthiness requirements to the product (airplane) on which either the part or assembly, or both, is to be installed, but not the AFM performance data, then the applicant should provide the applicable performance data in an FAA approved AFM or Aircraft Flight Manual Supplement (AFMS). Depending on the type and extent of change (as defined under “Section 3, CLASSIFICATION OF REPLACEMENT AND MODIFIED WHEEL/BRAKE CHANGES”) and either engineering or pilot judgment, or both, FAA approval will be determined by compliance with the following substantiation requirements:
(1) Replacement Wheel, Wheel/B rake Parts or Assemblies
(a) Brake-Anti-skid Compatibility
Replacement part or assembly changes, or both, defined under paragraph 3(d)(2) above titled “Minor Design Changes,” are considered to be minor whether: 1) they are proposed by the original wheel and brake manufacturer who holds the TSO authorization or 2) by another manufacturer seeking to produce a replacement part or assembly. While such changes are not expected to affect braking performance, functional landings may be required as a minimum to verify airplane/pilot/brake/anti-skid combination compatibility (reference part 23, § 23.735(d)). Normally five noninstrument functional landings are necessary to verify this compatibility.
(b) Brake Rotors/Stators In general, changes to the friction surfaces of the aircraft brake, including the stator and rotor, are considered to represent a major change by 3.d.(1), titled “Major Design Changes,” unless it can be shown the change cannot affect: 1) the airplane stopping performance, 2) brake energy absorption
70 characteristics, or 3) continued airworthiness (reference part 23, § 23.735(a)/(e)). In addition, if changes in heat sink friction components are proposed, certain provisions of 4.b.(2), titled “Modified Wheel, Wheel/Brake Parts, or Assemblies,” may also be applicable. Changes to continuing airworthiness, such as thermal control, and vibration control, should also be considered for the major/minor determination. The original manufacturer of the wheel or wheel/brake assembly who holds the TSO authorization may possess sufficient data to show that such changes could be considered minor (for example, airplane performance would not be affected). On the other hand, a manufacturer other than the original manufacturer who may wish to produce replacement rotors and stators may not have enough data to show that performance would not be affected. In this case, the major/minor status would be determined by applicable dynamometer tests by TSO-C26d and some functional airplane tests as a minimum.
(c) Brake Performance Equivalency It may be difficult to determine identicality but a finding of equivalency can be shown by additional design, analysis, and dynamometer tests as applicable. A change to an approved part that is determined to be minor can be validated on the dynamometer by: 1) a controlled test at the maximum certified kinetic energy capacity of the original brake assemblies from TSOA, or 2) the dynamometer testing may be done to the design landing and accelerate-stop kinetic energy levels appropriate to the aircraft [Reference part 23, § 23.735 (a) through (e)]. The following dynamometer test protocol is acceptable to validate replacement rotors/stators proposed by an applicant other than the original TSO holder:
1. Use of new stator or rotor parts in the replacement manufacturers’ brakes for each dynamometer test will be required to minimize test configuration variables. If rebuilt or in-service components other than these fail during testing, it should be realized the results may be questionable. Suspect tests would be inspected by the FAA, and retesting may then be necessary. Test methods, test hardware (including the tire size, ply and condition), and test procedures should be the same to ensure proper comparative evaluations. If brake friction materials are being compared, the heat sinks to be used for maximum certified Kinetic Energy (KE) testing should not have been subjected to test energies higher than design landing energy.
2. The maximum certified KEs approved under TSOA for the original manufacturer are proprietary data. Therefore, a PMA applicant that wants to maintain the TSOA status of a modified assembly will have to do the testing in this paragraph without knowing the kinetic energy levels the OEM tested for the TSOA. A series of tests may be necessary for a replacement manufacturer to reach the maximum
71 certified level of the original manufacturers brake. For each succeeding run, the KE will be increased by at least five percent over the previous run until the maximum certified KE level is reached. The initial KE level for this series of tests will be at the discretion of the applicant. If maintaining the TSOA is not desired, the PMA applicant may perform dynamometer tests at the airplane derived kinetic energy levels.
3. Maximum braking force pressure, de rived from the airplane maximum brake pressure capability, is to be applied during the tests.
4. Fuse plugs may be released or the tire deflated after each test run to reduce the risk to test personnel.
5. A minimum of five functional landings for anti-skid equipped airplanes and a minimum of three functional landings for non-anti-skid equipped airplanes, are needed.
(d) Worn Brakes [optional]
While there are no provisions under part 23 to require evaluating brake performance using worn brakes, there have been rejected takeoff accidents in which the brakes on subject airplanes were at or near their worn state of energy absorption capability and stopping capability. Therefore, as an optional test to a replacement brake performance evaluation (when there is question about variances in worn brake performance), it is recommended that such an assessment on the dynamometer be undertaken to support compliance with maximum Rejected Takeoff (RTO) performance in the AFM.
Dynamometer tests simulating a maximum energy RTO should be performed on the replacement brake assemblies with individual brakes within 10 percent of their wear limit (for example, at least 90 percent worn). The tests, used to verify the safety of a replacement brake system and to determine the maximum energy absorption capability of brakes in their fully worn state, should be substantiated as being representative of airplane and runway conditions.
(2) Modified Wheel, Wheel/Brake Parts, or Assemblies
(a) Modified Brake Design This laboratory and airplane test requirement applies to adding a major change brake design to an existing airplane for which FAA approved braking performance test data exists. Testing may be performed either for performance credit or to the existing performance level of the aircraft. As provided under examples of 3.d.(1), a modified brake is one that contains new or modified parts that may cause a significant variance in the kinetic energy absorption characteristics, AFM stopping distances and continuing airworthiness of the brake [reference 14 CFR, § 23.735 (a) through (e)].
Substantiating laboratory and airplane flight testing required for approval of a major changed brake will include:
1. For improved performance (see the following NOTE) (aa) Applicable dynamometer tests under TSO-C26d.
(bb) Instrument flight tests to include six takeoffs and six landings.
The six landings are to be conducted on the same wheels, tires, and brakes. All tests should be conducted with engines trimmed to the high side of the normal idle range, if applicable. The engine idle schedule may include a flight-idle schedule that may be applicable to the test.
(cc) Additional tests may be necessary for each airplane configuration change (for example, takeoff flaps, landing flaps, nose wheel brakes, anti-skid devices inoperative, and deactivation of wheel/brakes).
(dd) Brake system response evaluation.
(ee) Parking brake adequacy. Tires are allowed to skid during maximum power engine checks. Alternate braking system stops.
(ff) Fuse plug evaluation.
(gg) Anti-skid compatibility on wet runway.
(hh) Taxi tests, to ensure that ground handling, maneuvering, and brake sensitivity are satisfactory, should be conducted.
(ii) At least two braking stops, one at maximum takeoff weight and one at minimum landing weight, should be conducted on a wet runway to verify brake and anti-skid compatibility.
NOTE: Improved performance implies an increase in the friction coefficient (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.
2. For equivalent performance (see the following NOTE) (aa) Applicable dynamometer tests under TSO-C26d.
(bb) A sufficient number of conditions to verify the existing approved performance levels (RTO and landing for either TSOA levels or AFM levels). Consideration should be given to verification of fuse plugs, performance verification at appropriate energy levels, and configuration differences, including anti-skid on and off.
73 (cc) Taxi tests, to ensure that ground handling, maneuvering, and brake sensitivity are satisfactory, should be conducted.
(dd) At least two braking stops, one at maximum takeoff weight and one at minimum landing weight, should be conducted on a wet runway to verify brake and anti-skid compatibility.
NOTE: Equivalent performance implies that enough data will be obtained to verify the performance level for the change is equal to or better than the existing performance levels. The change may be to change the CG envelope, or for airplane configuration changes (such as flap angles), and may apply to specific operations (such as landings).
3. For extended performance (see the following NOTE) (aa) Applicable dynamometer tests under TSO-C26d. Consideration should be given to the items in section 4b(2)(a)(2).
(bb) A sufficient number of conditions to define the extended life and determine equivalency to the existing performance levels.
Consideration should be given to the items in section 4b(2)(a)(2).
NOTE: Extended performance implies the existing certification μ versus energy line will extend to establish the braking force level for a proposed change, such as gross weight or the desired maximum energy level, and may be applied to a specific operation (such as landing only).
(b) Modified Anti-skid System
This airplane test requirement applies to adding a new anti-skid system or changes to an existing anti-skid system that may affect airplane performance (for example, new anti-skid system, or a change from couple to individual wheel control). A sufficient number of either airplane performance tests or functional tests, or both, should be conducted to verify existing approved performance anti-skid "on" levels. If an increase of braking performance is desired, full airplane performance testing will be required [reference part 23, § 23.735 (d)].
(c) Modified Fuse Plugs/Wheels This item covers adding a significant modification to any portion of the existing wheel design on an airplane (change of wheel design, redesign, or relocation of fuse plugs). The following airplane tests can be performed when such changes are made:
1. One airplane-braking test should be conducted to show the fuse plugs would release when excessive energies are absorbed.
2. One airplane-braking test should be conducted to verify the maximum kinetic energy at which fuse plugs will not release (fuse plug substantiation). Dynamometer tests are not acceptable for this test.
NOTE: Wheel fuse plug integrity should be confirmed during braking tests where the energy level simulates the maximum landing energy. It should be shown the wheel fuse plugs will remain intact and that unwanted releases do not occur. One acceptable method to determine this is as follows:
(aa) Set engine idle thrust at the maximum value specified (if applicable). The engine idle schedule may include a flight-idle schedule that may be applicable to the test.
(bb) Set tire pressures to the minimum value appropriate for the airplane test weight.
(cc) Taxi at least three miles (normal braking, at least three intermediate stops, and all engines operating).
(dd) Conduct accelerate-stop test at maximum landing energy, keeping the deceleration rate consistent with the values used to determine performance distance.
(ee) Taxi at least three miles (normal braking, at least three intermediate stops, and all engines operating).
(ff) Park in an area to minimize wind e ffects until it is assured that fuse plug temperatures have peaked and that no plugs have released.
Instead of simulating the maximum kinetic energy landing during an accelerate-stop test, a landing and quick turnaround may be performed. Caution should be exercised to prevent jeopardizing the safety of the flight crew and airplane if the wheel plugs release after liftoff, requiring a landing to be made with some flat tires. The following elements should be included in the tests:
1. Set engine idle thrust at maximum value specified (if applicable).
2. Set tire pressures to the minimum value appropriate to the airplane test weight.
3. Conduct a landing stop at maximum landing energy, keeping the acceleration rate consistent with the values used to determine performance distance.
4. Taxi to ramp (three miles minimum with normal braking, at least three intermediate stops, and all engines operating).
5. Stop at the ramp. Go immediately to taxi for takeoff.
6. Taxi for takeoff (three miles minimum with normal braking, at least three intermediate stops, and all engines operating).
7. Park in an area to minimize wind effects until it is assured that fuse plug temperatures have peaked and that no plugs have released. Fuse plug protection of wheels and tires should show the fuse plugs would release when excessive energies are absorbed. Normally, this will occur during RTO performance tests.
(d) Accelerate Stop Tests
Accelerate-stop tests for commuter category airplanes and other airplanes are defined under part 23, §§ 23.55 and 23.735 (e). Accelerate-stop tests should be conducted for all modified wheel, wheel/brake parts or assemblies involving a major design change when this testing was performed to certify the original brake assembly. Such tests should include substantiation of the critical maximum brake energy stop (highest ground speed based on the V1 speed applicable to the maximum altitude and temperature the airplane is certified for according to the FAA approved AFM). On airplanes with wheel fuse plugs, a satisfactory demonstration of fuse plug compatibility should be conducted as stated under item (2)(c) titled, “Modified Fuse Plugs/Wheels.”
(e) Other Substantial Airplane Tests
Depending on the extent of wheel, wheel/brake part, or assembly modifications that may be involved, there will be several airplane tests that should be considered as well as those above. As applicable to specific changes and to the type of part 23 airplane involved, the following are tests that may be appropriate and required by the FAA for approval:
1. Brake Kinetic Energy (K E) Absorption Tests Verify the brake KE absorption test determined by the laboratory test meets the TSO requirements and the airplane manufacturers requirements (to be identified by the FAA) [reference part 23, § 23.735(a) through (e)]. The engine idle schedule may include a flight-idle schedule that may be applicable to the test.
2. Brake Pressure Test Verify brake pressure tests conducted under the TSO are satisfactory for the brake system pressure on the airplane, as determined by the manufacturer's brake system pressure data. Conduct a brake pressure
76 test on the airplane if manufacturers brake system data is not available to verify the adequacy of the TSO test [reference part 23, § 23.735(c)].
3. Taxi Ground Handling Tests
Perform taxi tests to assure that ground handling, controllability, maneuverability, and brake sensitivity are satisfactory. Use normal braking, intermediate stops, with all engines operative [see 4b(2)(a), Modified Brake Design].
4. Wet Running Tests
Perform brake stops on a wet runway to verify brake and, if applicable, anti-skid system compatibility [see 4b(2)(a), Modified Brake Design].
5. Function Reliability Tests Perform function reliability landing stops. Normally six maximum brake landings should be satisfactorily conducted on the same set of wheels, tires, and brakes [see 4b(2)(a), Modified Brake Design].
6. Landing Performance Tests Determine the landing performance is adequate to the previously approved performance data shown in the AFM. If the AFM performance data is not available because it is not required by the airplane certification basis, the manufacturers data (if available) provided to the pilot should be used as a basis for comparison [see 4b
(2)(a) Modified Brake Design].
7. Static Torque Tests Determine whether there is enough static torque when parked and during appropriate engine run up conditions [reference part 23, § 23.735(b)].
8. Brake Response Tests During the tests, brake response characteristics should be monitored for unacceptable vibrations, squeal, fade, grabbing, and chatter. These characteristics may have a destructive effect on the brake assembly components and may be relevant to endurance of landing gear system components.