of deceleration and, therefore, for the same amount of kinetic energy, a higher initial brakes-on speed would result in a lower rate of energy absorption. Such a situation is recognized and is similarly stated in TSO-C135, which provides an acceptable means for brake approval under § 25.735(a).
(c) For certification purposes, a brake having a higher initial brakes-on speed is acceptable if the dynamometer test showed that both the energy absorbed and the energy absorption rates required by § 25.735(f) had been achieved.
(d) Brake qualification tests are not intended as a means of determining expected airplane stopping performance, but may be used as an indicator for the most critical brake wear state for airplane braking performance measurements.
g. Brake condition after high kinetic energy dynamometer stop(s). (Reference § 25.735(g)).
(1) Following the high kinetic energy stop(s), the parking brake should be capable of restraining further movement of the airplane and should maintain this capability for the period during which the need for an evacuation of the airplane can be determined and then fully accomplished. It should be demonstrated that, with a parking brake application within a period not exceeding 20 seconds of achieving a full stop, or within 20 seconds from the time that the speed is retarded to 20 knots (or lower), in the event that the brakes are released prior to achieving a full stop (as permitted by TSO-C135), the parking brake can be applied normally and that it remains functional for at least 3 minutes.
(2) Practical difficulties associated with dynamometer design may preclude directly demonstrating the effectiveness of the parking brake in the period immediately following the high energy dynamometer stop(s). Where such difficulties prevail, it should be shown that, for the 3-minute period, no structural failure or other condition of the brake components occurs that would significantly impair the parking brake function.
(3) Regarding the initiation of a fire, it should be demonstrated that no continuous or sustained fire, extending above the level of the highest point of the tire, occurs before the 5-minute period has elapsed. Neither should any other condition arise during this same period or during the stop, either separately or in conjunction with a fire, that could be reasonably judged to prejudice the safe and complete airplane evacuation.
Fire of a limited extent and of a temporary nature (e.g., those involving wheel bearing lubricant or minor oil spillage) is acceptable. For this demonstration, neither firefighting means nor coolants may be applied.
h. Stored energy systems.
(1) Stored energy systems use a self-contained source of power, such as a pressurized hydraulic accumulator or a charged battery (refer to § 25.735(h)). This requirement is not applicable for those airplanes that provide a number of independent 13
braking systems, including a stored energy system, but are not "reliant" on the stored energy system for the demonstration of compliance with § 25.735(b).
(2) The indication of usable stored energy should show:
(a) The minimum energy level necessary to meet the requirements of §§ 25.735 (b)(1) and (h) (i.e., the acceptable level for dispatch of the airplane);
(b) The remaining energy level; and
(c) The energy level below which further brake application may not be possible.
(3) If a gas pressurized hydraulic accumulator is to be used as the energy storage means, indication of accumulator pressure alone is not considered adequate means to indicate available stored energy, unless verification can be made of the correct precharge pressure with the hydraulic system pressure off and the correct fluid volume with the hydraulic system pressure on. Furthermore, additional safeguards may be necessary to ensure that sufficient energy will be available at the end of the flight.
Similar considerations should be made if other stored energy systems are used.
(4) A full brake application cycle is defined as an application from brakes fully released to brakes fully applied, and back to fully released.
i. Brake wear indicators. The indication means should be located such that no special tool or illumination (except in darkness) is required. Expert interpretation of the indication should not be necessary (refer to § 25.735(i)).
j. Overtemperature and overpressure burst prevention. Generally, two separate types of protection should be provided: one specifically to release the tire pressure should the wheel temperature increase to an unacceptable level, and the other to release the tire pressure should the pressure become unacceptably high, particularly during the inflation process. The temperature sensitive devices are required in braked wheels only, but the pressure sensitive devices are required in all wheels (refer to §§ 25.735(j) and
25.731(d)).
(1) The temperature sensitive devices (e.g., fuse or fusible plugs) should be sufficient in number and appropriately located to reduce the tire pressure to a safe level before any part of the wheel becomes unacceptably hot, irrespective of the wheel orientation. The devices should be designed and installed so that once operated (or triggered) their continued operation is not impaired by the releasing gas. The effectiveness of these devices in preventing hazardous tire blowout or wheel failure should be demonstrated. It should also be demonstrated that the devices will not release the tire pressure prematurely during takeoff and landing, including during “quick turnaround” types of operation.
(2) It should be shown that the overpressurization devices, or the devices in conjunction with the tire inflation means permanently installed in the wheel, would not permit the tire pressure to reach an unsafe level regardless of the capacity of the inflation source.
(3) Both types of devices should normally be located within the structure of the wheel in positions that minimize the risk of damage or tampering during normal maintenance.
k. Compatibility. Compliance with § 25.735(k) may be achieved by the following:
(1) As part of the overall substantiation of safe and anomaly free operation, it is necessary to show that no unsafe conditions arise from incompatibilities between the brakes and brake system with other airplane systems and structures. Areas that should be explored include antiskid tuning, landing gear dynamics, tire type and size, brake combinations, brake characteristics, brake and landing gear vibrations, etc. Similarly, wheel and tire compatibility should be addressed. These issues should be readdressed when the equipment is modified.
(2) During brake qualification testing, sufficient dynamometer testing over the ranges of permissible brake wear states, energy levels, brake pressures, brake temperatures, and speeds should be undertaken to provide information necessary for systems integration.
/s/ Ali Bahrami Ali Bahrami Acting Manager Transport Airplane Directorate Aircraft Certification Service 15