(4) Amendment 25-52 (June 2, 1980) revoked part 37, § 37.167 Aircraft Tires - TSO- C62c. Subpart A of 14 CFR part 37 became Subpart O of 14 CFR part 21. Subpart B of 14 CFR part 37 was eliminated, and the technical performance standards were made available at FAA Headquarters.
(5) Amendment 25-72 (July 20, 1990) deleted the requirement to consider the effects of inertia, from § 25.733(a)(1) because such effects were determined to be negligible for constant speed taxi and takeoff conditions. In addition, § 25.733(c)(1) changed from a reference to § 25.733(a)(1) to a direct statement of the loading conditions for the sake of clarity.
(6) Amendment 25-78 (March 29, 1993) added paragraph § 25.733(e) to require that for airplanes with a maximum certified takeoff weight of more than 75,000 pounds, the tires mounted on braked wheels be inflated with dry nitrogen or other inert gases so that the tire does not contain oxygen in excess of 5 percent by volume to prevent tire explosions. The 75,000 pounds weight limit was based on a review of the service difficulty reports indicating that tire explosions, as opposed to tire bursts, tend to occur on the larger, heavier airplanes. The 5 percent by volume limit for oxygen content was based on a series of laboratory tests indicating that an abrupt auto-ignition could occur for oxygen concentrations of 10 percent or more.
(a) There had been several cases where tire explosions had occurred in transport category operations. A tire explosion differs from a tire burst, which can occur when an overheated or over inflated tire fails and releases the high pressure air contained therein.
Protection against tire burst is required under § 25.729(f). A tire explosion is the result of a chemical reaction occurring when gases released from overheated tire material mix with oxygen in the inflation air and ignite. In 1987, the FAA issued an airworthiness directive (AD 87-08-09) requiring use of nitrogen for tire inflation to ensure that the tires on braked wheels of airplanes do not contain more than 5 percent oxygen. Amendment 25-78 was intended to accomplish the same purpose for new airplanes.
d. Policy/Compliance Methods. For guidance on compliance with this requirement, refer to the preamble of this rule and the following information.
(1) Approval of Retreaded Tires by Similarity. The following is extracted from an FAA memorandum dated March 1, 1995, that addresses whether “qualification by similarity” basis could be used for approving the production of retreaded aircraft tires, using a modified tread compound, in various sizes.
(a) Background. A tire manufacturer had qualified several retreaded tires of different sizes in accordance with the stipulations of advisory circular (AC) 145-4, Inspection, Retread, Repair, and Alteration of Aircraft Tires (dynamometer testing). The manufacturer wished to produce other retreaded tires of different sizes and ratings, based on similarity. In the past, every tire size had to be tested for such an approval.
(b) Supportive Information. The following supportive information was provided:
1 Nature of the Change The formulation for the tread compound used to retread commercial aircraft tires had been modified as follows:
(aa) Polymer: A proprietary description of the change.
(bb) Filler: A proprietary description of the change.
2 Test Results. The change in tread compound had been proven by dynamic qualification testing on a sample of tire sizes. The various tire sizes were representative of the tire sizes listed for production approval in the applicant's letter. Qualification Test Reports (QTR’s) were submitted to the FAA. The QTR’s were approved by the cognizant Flight Standards District Office.
3 Physical Properties of the Tread Material. The physical properties measured in a laboratory showed that the new compound had a specific percent lower hysteresis value, an indicator of heat generation. This characteristic provided an indication of tread durability, and related to the qualification of tires that had been retreaded using the new compound. Also, this lower modulus and a lower hardness of the new compound indicated a better resistance to scuffing and tearing actions to which the tire is subjected in service.
4 Static Test Results per AC 145-4. Because the tire design remained the same, all static measurements (overall diameter, section width, static-loaded radius, skid depth, and static unbalance) were not affected by this change. Tread weight remained within the retread process capability.
5 In-Service Evaluation. Tires retreaded with this new material had been evaluated in service with several different airlines. No problems had been reported by the operators and no tires had been prematurely removed from service due to tread-related conditions, such as chunking or tread separation. Field inspection and examination of returned worn casings, performed by qualified personnel, had indicated good tread integrity and wear characteristics. Based on cycle data gathered (number of landings per retread), the length of the maintenance interval remained within a reasonable percentage of the baseline tire.
6 Rationale Summary. The tire sizes selected to demonstrate the continuation of performance were representative of the tire sizes for which production approval was requested. At least one tire size was qualified in each of the tire design types presently in service. For each tire application (nose and main landing gear), at least one tire was dynamically qualified. With one tire size, the highest speed rating in the list of proposed tire sizes was successfully qualified. With another tire size, the tested sample included the highest rated pressure tire. With yet another tire size, the largest skid depth in the list of proposed sizes was 23
dynamically tested. Within their own class of tires, these were, historically, the most difficult sizes to meet the qualifications of the AC 145-4 requirements. They had often been used in the past to prove process or material changes.
7 In view of the substantiating factors detailed above, it was requested that all of the additional tire sizes listed in their letter be authorized for production on the basis of “qualification by similarity.”
(c) Approval. The FAA carefully considered the information provided above, and determined that there was sufficient merit to authorize production of the additional tire sizes for retreading, based on ”qualification by similarity.”
(2) Approval of Nonretreadable Tires - Qualification Testing. The following is extracted from an FAA memorandum dated August 18, 1988, which addresses the definition and application of "major and minor" changes as they relate to products with a TSO versus aircraft installation approval.
(a) TSO tire dynamometer testing, alone, is not considered acceptable for installation approval except for the most straightforward changes. This memorandum also addresses a potentially unsafe condition that may have resulted from retreading tires that were designed and approved as nonretreadable.
1 Based on evidence presented, including the adverse service history, it appears that the development of the lightweight and nonretreadable tires should have been classified as a "major change," which would have necessitated flight testing on the candidate airplane(s) prior to approval.
(b) It was noted that the TSO was granted based on dynamometer testing, and that the tire was presumably shown to meet the required load-speed-time curve, and other airplane weight and load parameters. However, FAA policy has been that dynamometer testing is not a suitable substitute for airplane tests for any but the most straightforward changes.
(c) The memorandum recommended that a suitable test program be implemented as soon as possible that would demonstrate that these tires are appropriate for their intended application. The test program that was established in January 1984, for the introduction of radial tires, presented later in paragraph (4)(b), is also appropriate in this case since the effect of these tires on airplane performance, landing gear dynamics and antiskid operation, wheel/fuse plug integrity, brake energy absorption, and wheel-well tire burst, is unknown. These lower weight, and therefore lower strength, tires may have a profound effect on the airplane performance, the wheel/brake integrity, or the life of the tires. The documentation that accompanies nonretreadable tires, once they are approved, must clearly show that the tires are not to be retreaded.
(d) There is concern that there have been many changes to wheels, tires, and brakes that have been considered to be "product improvements," and approved under the TSO 24
system as "minor changes," that should have been demonstrated on the airplane prior to their approval.
(3) Approval Method for Substitute Tires. The following is extracted from an FAA memorandum dated April 14, 1988, which addresses the certification considerations that should be taken into account when the installation approval of a new tire on a type certificated aircraft is requested.
(a) A substitute tire must be shown to be adequate for its intended use. In some cases, the proposed tire will be listed in the airframe manufacturer's specification documents, and can be installed without further investigation. The airframe manufacturer should be contacted to determine if data exist regarding the acceptability of the proposed tire to be substituted on the airplane.
(b) If the replacement tires are of the same basic type and construction as the currently approved tires, but they have not been previously approved on the airplane, the following items should be considered. This list is not meant to imply that flight tests would be mandatory; rather, that the items should be discussed with the applicant and any discrepancy or concerns addressed.
1 The TSO load-speed-time curves should be compared to the airplane envelope to establish the suitability of the proposed tire for installation on the airplane. If the tire is not TSO authorized, it would be the applicant's responsibility to demonstrate that the tire meets all TSO requirements.
2 The physical dimensions of the mounted tire should allow adequate clearance to the wheel well and its contents, landing gear structure, gear doors, etc.
Consideration should be given to new tires as well as retreads and possible growth effects of retreading.
3 If the weight of the proposed tire is significantly different from the original, or from other tires approved on the airplane, landing gear retraction times or emergency gear extension operation may be affected. A flight test should be conducted if there is a concern that any weight difference would be large enough to affect gear actuation times.
4 The spring rates for the proposed tire should be compared to other tires approved for the specific airplane at the expected load and deflection, to determine any adverse effect on the loads on the landing gear or any adverse dynamic coupling between the landing gear and tires.
5 The tire rolling radius, tire pressure, tire deflection, and tire footprint should be compared to other tires approved on the airplane, to determine the effect on water spray patterns or tire heating. If the tire pressure is adjusted to obtain a certain deflection, the effect on tire load carrying capability should be investigated.
6 Uninstrumented functional landings should be conducted. If antiskid is installed, these functional landings should be conducted on both wet and dry runways to determine if any adverse effects on the system have been introduced by the proposed tire.
7 If comparison of the proposed tire to other tires approved on the airplane reveals any significant differences in the factors noted above, or if there is evidence of significantly increased or decreased tire rolling resistance or tire µ, performance landings should be conducted. Increased tire rolling resistance could impact takeoff performance, decreased rolling resistance could affect fuse plug integrity, and a different tire µ could affect stopping performance.
(4) Replacement of Bias Ply Tires with Radial Ply Tires. The following is extracted from an FAA memorandum dated February 7, 1984.
(a) This memorandum provided certification criteria for installation of radial tires on type certificated aircraft which only had bias tire approval. The radial tire had obtained TSO approval and this memorandum outlined the installation considerations.
(b) Certification Program for Replacing Bias Tires with Radial Tires, part 25 Transports; All weight Categories, dated Jan. 12, 1984. A bias ply to radial ply tire change is not considered minor. The following certification program is designed for a TSO approved radial tire that is to replace a bias tire of equivalent rating.
1 The tire must be TSO-C62c approved, or equivalent as stated in § 25.733(c), and rated for the speed and gross weight under consideration. The radial tire must have been tested to the equivalent of the TSO, i.e., loads, speeds, and energies, etc.
2 The vertical spring rate for the radial tire should be determined and compared to the original bias tire in order to assess the difference in energy absorption characteristics. The airplane vertical load factors should not exceed the original design values with the radial tire installed. Also, spin-up and spring-back loads should be evaluated if there are significant differences in the weight and moments of inertia of the two tire and wheel assemblies.
(For guidance on compliance refer to §§ 25.479, 25.723, and 25.725.)
3 The protection of the equipment in the wheel wells should be reassessed as the radial tire will have different failure burst characteristics than the bias tire. This assessment should cover tire air blast, as well as loose tread. (For guidance on compliance refer to § 25.729(f).)
4 Emergency gear extension should be reviewed and, if necessary, reassessed if tire size or weight changes are involved. (For guidance on compliance refer to § 25.729(c).)
5 A maximum Rejected Takeoff (RTO) energy stop using the 3 mile taxi, 3 full stops criteria of AC 25-7A, Flight Test Guide for Transport Category Airplanes, chapter 4, section 4, paragraph 55, should be conducted.
(aa) The tire pressure is to be set to the highest value appropriate for the maximum takeoff weight for which approval is being sought. Pressure should be set before taxi and with cold tires. This test is specified to confirm (at maximum takeoff weight) acceptable tire structural integrity, tire anti-skid dynamics, airplane braking performance, effectiveness of the fuse plugs, and to assess the directional control compatibility of the airplane if the fuse plugs melt late in the RTO run. In addition, the fire limitations of AC 25-7A, paragraph 55c(ii), or latest revision, are to be observed.
6 A sufficient number of RTO's and landings should be conducted to substantiate that the aircraft performance with radial tires is as good as, or better than, originally demonstrated with bias tires. Tests should be conducted in accordance with AC 25-7A, paragraph (2)(ii)(c), or latest revision.
7 The fuse plug integrity no-melt tests should be conducted in accordance with AC 25-7A, paragraph 55c(7), unless the applicant demonstrates the energies absorbed by the brake with a radial tire are no greater than the energies absorbed in the same brake when using the bias tire when comparing equivalent flywheel energies on the dynamometer. The fuse plug integrity test should also be run if the brake or tire temperatures of the radial tire/wheel/brake assembly are greater than the brake or tire temperatures of the bias tire/wheel/brake assembly when comparing equivalent flywheel energies on the dynamometer.
8 A sufficient number of flight tests should be conducted on wet and dry runways to establish that the anti-skid and/or autobrakes will function compatibly and acceptably with the radial tires.
9 A high speed takeoff at the highest speed for which approval is being sought, and sufficient taxi and turn tests to assess dynamic stability should be conducted.
1 0 If the airplane is approved for unimproved runways, additional evaluations should be conducted if there is an appreciable change in the tire footprint.
1 1 Water spray characteristics should be reviewed and, if necessary, reassessed.
1 2 Tire intermix, radial/bias, should be considered based on an evaluation on a case by case basis. For example, some of these items (1-11) may not apply for a nose tire 27
intermix. Any additional considerations deemed necessary by the cognizant ACO should be addressed.
1 3 If there is a significant tire tread change from one radial tire to another radial tire, the airplane performance should be considered and if necessary reassessed.
1 4 Additional testing may be required if certification for an increase in airplane weight or kinetic energy is requested.
(5) Certification of Radial Tire Installation. The following is extracted from an FAA memorandum dated March 28, 1984, which addresses as to why is it necessary to consider items
(4)(b)1. through (4)(b)14. addressed in the preceding paragraph, and provides historical information on the reasons for certain items contained in the radial tire certification program. It also explains some of the reasons why dynamometer testing alone is not considered adequate for installation approval of replacement tires.
(a) The "Certification Program for Replacing Bias Tires with Radial Tires" dated January 12, 1984, is still the FAA recommended program. A bias ply tire to radial ply tire change is not considered minor. Dynamometer tests are not an acceptable substitute for airplane tests for tires, wheels, and brakes. This position, which is supported by FAA certification experience, is taken in AC 25-7A, chapter 4, section 4, paragraph 55.
1 For example, the FAA was requested to certificate a medium transport with three sets of tire/wheel/brake combinations for an increased gross weight. The manufacturer wished to certificate these combinations based on extrapolated data from existing lower energy data of one set, and to the higher TSO authorized energy levels of all three sets;
however, the FAA insisted a full testing program be done. All three sets failed to achieve the projected braking coefficient of friction (µ). In addition, the set that was supposed to have the greatest margin, the set designated for future growth potential, almost failed due to shearing of the brake rotor lugs. The wheels, tires and fuseplugs functioned properly.
(b) Another example was the certification of a new model large transport. The tires had received TSO authorization, but were failing at the high speed takeoffs within the TSO performance envelope. Going further back, the FAA has had similar experiences relative to fuseplugs, anti-skid brake lock-up, and so forth. These experiences confirm that the dynamometer is not a satisfactory tool in predicting performance, compatibility, fuseplug melt/no-melt, etc., for tires, wheels, and brakes. The dynamometer is even questionable when it is used for trend data, as demonstrated by the medium transport example above. It is, however, useful as background information.
(c) That the dynamometer does not accurately simulate actual conditions may be due to its inherent inability to adequately simulate the following:
1 Actual runway conditions (i.e., round versus the flat surface of the runway, surface conditions and so forth).
2 Thermodynamic interaction (i.e., conduction. radiation, and convection between adjacent tires, wheels, and brakes, between the tire and the runway surface, and the effects of the air).
3 Airplane/System dynamics (i.e., the interaction between the airplane and supporting gear and systems, control systems and so forth).
(d) Adequate means of simulation could probably be developed with new test criteria (if comparisons are to be made) and new techniques. The end result would most likely be a test fixture on a track with a complete landing system including supporting structure, systems duplicating the number of landing gear, and so on, which would be capable of intricate simulations of takeoff, landing and braking dynamics. However, it would probably be less expensive to test the airplane as is currently the practice.
(e) Another problem is establishing the adequacy of the tire relative to the TSO data and to additional tests. The airframe manufacturer may request that the tire, wheel, and brake manufacturers conduct specific tests beyond the scope of the TSO. Side loading and overloading are good examples of additional tests. We can never be sure after completing the airplane tests that the tire (wheel or brake also) reliability is dependent totally on the TSO tests or on the TSO test and the additional tests specified. We are aware of at least one case where two tires manufactured by two different companies were installed on the same airplane and operated within the same TSO envelopes, yet one tire type failed while the other passed. The successful tire type had additional side loads specified which were not part of the TSO testing. As a repetitive statement, the FAA position is that TSO data is not a satisfactory substitute for tire wheel or brake tests on the airplane.
(f) If the radial ply tire is heavier than the bias tire, it must be determined whether that is significant. Lighter tire weight can affect some emergency extension systems as some of these systems use the landing gear weight to overcome the unlocking residual forces to provide enough inertia to extend the gear down, over center, and to lock the gear in place. Heavier weight may have an effect on retraction times. Radial tires may weigh as much as 1/4 less than the bias tires they would replace.
(g) Rejected takeoff tests are not only to prove the capability of the brakes, but also to prove the landing gear system and its interaction with associated components as well.
These tests are to evaluate performance, dynamics, and system adequacy. As stated earlier, the dynamometer tests of the TSO are not an acceptable equivalent or substitute for the airplane tests. We also note that an applicant has stated that: "The radial tire exhibits less drag, and would therefore result in a slightly longer stopping distance at the same brake pressure (i.e., brake torque)." The maximum RTO is conducted at the maximum brake pressure, therefore, the braking distance would appear to be longer, based on an applicant's comment. In addition to other considerations, the maximum RTO and other performance tests should help establish how much longer the braking distance is going to be.
(h) Note that for the same bias tire dynamometer test energy, the brake energy increases with a decrease in energy absorbed by the radial tire; therefore, the heat being delivered to the fuseplug through the wheel will probably increase. It is not known how much or how significant that increase will be. How the fuseplugs are going to act (no-melt/melt) should be established on the airplane prior to certification.
(i) A sufficient number of flight tests should be conducted on wet and dry runways to establish that the anti-skid and the landing gear system will function compatibly and acceptably with the radial tires.
(j) It should be established prior to certification that the airplane tire will behave structurally and dynamically on the airplane as well as it did on the dynamometer at high speed conditions. Because dynamic stability may be more of a function of gear dynamics coupled to the tire dynamics, airplane tests should be conducted, as the dynamometer is insufficient in simulating airplane and landing gear system dynamics.
(6) Critical Conditions & Maximum Ramp Weight Definitions. The following is extracted from an FAA telegraphic message dated January 26, 1981, which addresses definitions of "critical conditions" and "maximum ramp weight" as they relate to § 25.733.
(a) Section 25.733(a) Critical Conditions. The critical conditions are those conditions where the takeoff or landing speed extremes that have been established by evaluating takeoff or landing performance for temperature, altitude, aircraft weight, aircraft configuration, runway conditions, engine performance, etc., may approach the tire speed rating. The critical conditions in this case are the takeoff or landing performance conditions that establish maximum tire speed.
(b) Section 25.733(a)(1); (b)(1); (b)(3);Maximum ramp weight. The maximum ramp weight is the maximum weight allowed on the airplane (includes airplane weight, fuel, oil, baggage, etc.). This definition is used interchangeably with maximum taxi weight.
e. References. The addresses for ordering the latest revision of advisory circulars, technical standard orders, and other referenced documents listed below can be found in the Appendix to this AC.
AC 20-97A, High-Speed Tire Maintenance and Operational Practices.
AC 43.13-1A, Acceptable Methods, Techniques and Practices - Aircraft Inspection and Repair, chap. 8, L. G. Equipment.
AC 145-4, Inspection, Retread, Repair and Alterations of Tires.
FAA Order 8000.54, Process Specifications for Retreading Tires and Inspection Procedures Manuals for Tire Retreaders.
FAA Order 8000.64, Qualification of Aircraft Radial Tires for Use on Aircraft and for Retreading.
FAA's Tire Approval Process Video, MTS 422/422.1, 42:15 Minutes.
TSO-C62c, of § 37.167 14 CFR. This TSO was removed from regulations (§ 37.167, Amendment 25-52, 1980), and became a voluntary standard.
TSO-C62c, With Addendum I. This TSO was removed from regulations (§ 37.167, Amendment 25-52, 1980), and became a voluntary standard.
TSO-C62d, Tires.
SAE AIR-1904 - Tire Spray Suppression - Airplane, Design Consideration and Testing.
SAE ARP-1322 - Overpressurization Release Devices.
SAE ARP-4834 - Recommended Practice for Retreaded Aircraft Tires - Radial and Bias.
SAE AS-707B - Thermal Sensitive Inflation Pressure Release Devices for Tubeless Aircraft Wheels.
SAE-AS 1188 - Aircraft Tire Inflation-Deflation Equipment.
SAE AS-4833 - Aircraft New Tire Standard- Bias and Radial.
14. SECTION 25.735 - BRAKES.
a. Rule Text.
(a) Each brake must be approved.
(b) The brake system and associated systems must be designed and constructed so that if any electrical, pneumatic, hydraulic, or mechanical connecting or transmitting element (excluding the operating pedal or handle) fails, or if any single source of hydraulic or other brake operating energy supply is lost, it is possible to bring the airplane to rest under conditions specified in 25.125, with a mean deceleration during the landing roll of at least 50 percent of that obtained in determining the landing distance prescribed in that section. Subcomponents within the brake assembly, such as brake drum, shoes, and actuators (or their equivalents), shall be considered as connecting or transmitting elements, unless it is shown that leakage of hydraulic fluid resulting from failure of the sealing elements in these subcomponents within the brake assembly would not reduce the braking effectiveness below that specified in this paragraph.
(c) Brake controls may not require excessive control force in their operation.
(d) The airplane must have a parking control that, when set by the pilot, will without further attention, prevent the airplane from rolling on a paved, level runway with takeoff power on the critical engine.
(e) If antiskid devices are installed, the devices and associated systems must be designed so that no single probable malfunction will result in a hazardous loss of braking ability or directional control of the airplane.
(f) The design landing brake kinetic energy capacity rating of each main wheelbrake assembly shall be used during qualification testing of the brake to the applicable Technical Standard Order (TSO) or an acceptable equivalent. This kinetic energy rating may not be less than the kinetic energy absorption requirements determined under either of the following methods:
(1) The brake kinetic energy absorption requirements must be based on a rational analysis of the sequence of events expected during operational landings at maximum landing weight. This analysis must include conservative values of airplane speed at which the brakes are applied, braking coefficient of friction between tires and runway, aerodynamic drag, propeller drag or power-plant forward thrust, and (if more critical) the most adverse single engine or propeller malfunction.
(2) Instead of a rational analysis, the kinetic energy absorption requirements for each main wheel-brake assembly may be derived from the following formula, which must be modified in cases of designed unequal braking distributions.
KE = 0.0443 WV2 N where- KE = Kinetic energy per wheel (ft.-lb.);
W = Design landing weight (lb.);
V = Airplane speed in knots. V must be not less than VS0 , the power off stalling speed of the airplane at sea level, at the design landing weight, and in the landing configuration; and N = Number of main wheels with brakes.
(g) The minimum stalling speed rating of each main wheel-brake assembly (that is, the initial speed used in the dynamometer tests) may not be more than the V used in the determination of kinetic energy in accordance with paragraph (f) of this section, assuming that the test procedures for wheel-brake assemblies involve a specified rate of deceleration, and, therefore, for the same amount of kinetic energy, the rate of energy absorption (the power absorbing ability of the brake) varies inversely with the initial speed.
(h) The rejected takeoff brake kinetic energy capacity rating of each main wheelbrake assembly that is at the fully worn limit of its allowable wear range shall be used during qualification testing of the brake to the applicable Technical Standard Order (TSO) or an acceptable equivalent. This kinetic energy rating may not be less than the kinetic energy absorption requirements determined under either of the following methods:
(1) The brake kinetic energy absorption requirements must be based on a rational analysis of the sequence of events expected during an accelerate-stop maneuver.
This analysis must include conservative values of airplane speed at which the brakes are applied, braking coefficient of friction between tires and runway, aerodynamic drag, propeller drag or powerplant forward thrust, and (if more critical) the most adverse single engine or propeller malfunction.
(2) Instead of a rational analysis, the kinetic energy absorption requirements for each main wheel brake assembly may be derived from the following formula, which must be modified in cases of designed unequal braking distributions:
KE = 0.0443 WV2 N where- KE = Kinetic energy per wheel (ft.-lb.);
W = Design landing weight (lb.);
V = Airplane speed (knots);
N = Number of main wheels with brakes; and W and V are the most critical combination of takeoff weight and ground speed obtained in a rejected takeoff.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25-23, 35 FR 5676, Apr. 8, 1970; Amdt. 25-48, 44 FR 68742, Nov. 29, 1979; Amdt. 25- 72, 55 FR 29777, Jul. 20, 1990, as amended by Amdt. 25-78, 58 FR 11781, Feb. 26, 1993; Amdt. 25-92, 63 FR 8320, Feb. 18, 1998]
b. Intent of Rule.
(1) This rule requires use of approved brakes and wheel assemblies, either approved under an applicable technical standard order (TSO) e.g., TSO-C26c, or approved under the type certificate for the airplane. The existence of TSO approval with the article displaying required markings does not automatically constitute the authority to install and use the article on an airplane.
(2) It is the responsibility of those desiring to install this article to determine that the aircraft operating conditions are within the TSO standards. Additional requirements may be imposed based on airplane specifications, wheel and brake design, and quality control specifications. The airframe manufacturer/user must conduct the applicable airplane certification tests and receive FAA approval.
(3) In addition to brake performance and safety requirements, the rule provides standards for systems and equipment associated with brakes, e.g., control mechanisms and antiskid systems. The brake and wheel assembly must have proper energy and load ratings for taxi, takeoff, refused takeoff, and landing. The braking system must have acceptable pilot-control forces, adequate parking brake capability, emergency braking capacity and directional control, and protection against overpressure, overtemperature, and fire.