1. TSO Minimum Standard Performance Demonstration. The wheel and brake assembly containing the applicant’s proposed steel rotor configuration should successfully demonstrate compliance with the braking and structural tests of the applicable TSO, and
2. Compliance with the airplane manufacturer’s specified requirements, or the alternate procedures specified in paragraph 15.4.8.9.
15.4.8.9 Alternate Procedures (Steel Rotors Only).
15.4.8.9.1 Energy and Torque Capacity Tests.
A series of tests (not only one) may be necessary to demonstrate, in backto-back tests, that brake energy absorption and torque and pressure vs.
time profiles are equivalent. All friction components and structures should be in the new condition to obtain credit for this test. If rebuilt or in-service components other than these fail during testing, it should be realized that the results of the test(s) may be questionable. Suspect tests will be carefully reviewed by the FAA and may require retesting. Prior to test, the applicant should carefully document wheel hardness and wheel drive, torque tube spline, piston/bushing assembly conditions to assure comparable test articles are being used. The same tire size and ply rating, manufacturer, tire condition, radial load, and rolling radius should be used in each test. Test machines and test conditions should be consistent from test to test, including test brake, wheel and tire break-in stop histories, brake pressure onset rates (pound-force per square inch gauge per second) (psig/sec), maximum pressures, initial brakes-on-speeds, flywheel inertias, etc., to assure consistent test control. Artificial cooling is not permitted during or subsequent to the test until wheel and piston housing temperatures have peaked.
15.4.8.9.2 The initial kinetic energy (KE) level for this series of tests will be at the discretion of the applicant. For each succeeding run, the KE will be increased by approximately 5 percent over the previous run, until the ultimate KE level is determined (i.e., points at which pistons are about to exit bores or flywheel deceleration falls below 3 ft/sec2 (one-half of the TSO RTO minimum average deceleration requirement). The deceleration reported by the applicant should be based upon distance (and not time) in accordance with the following formula:
1. A minimum of two runs at this ultimate energy level should be conducted on the original manufacturer’s wheel and brake assembly for baselines. These test runs should show similar results. Maximum braking force pressure should be applied during the tests. Fuse plug
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releases in any tests should demonstrate safe release of approved nitrogen-air mixtures.
2. A minimum of two test runs at the ultimate energy level should then be conducted on the applicant’s proposed wheel and brake assembly
(i.e., a back-to-back demonstration of the two manufacturers’ brakes).
Tests should show similar brake energy absorption, torque, and thermal performance capabilities, and torque and pressure versus time profiles, while demonstrating sealing and structural integrity comparable to the original manufacturer’s wheel and brake assembly.
15.4.8.9.3 Worn Brake RTO Capability.
Worn brake RTO capability for the proposed wheel and brake assembly with steel rotor replacement configuration(s), and at the wear pin limit(s) proposed by the applicant, should be established during dynamometer test(s). The test brake energy absorption criteria, torque performance, and pass/fail requirements should be requested of the airplane manufacturer to provide supporting evidence that the worn brake RTO capability is equivalent to that achieved with the original TSO holder’s wheel and brake assembly(ies). If unavailable, the applicant should propose a worn brake RTO test plan similar to that in paragraph 15.4.4 for new brakes.
The applicant should also propose to the FAA the method which will be followed by the applicant to verify that the worn brake RTO capability of in-service worn brakes with replacement rotors is equivalent to the capability established in initial dynamometer test(s) in accordance with paragraph 15.4.4.2.1 of this AC.
15.4.8.9.4 Intermixing of steel rotor assemblies produced by two manufacturers will not be allowed until it can be demonstrated that wear patterns of the intermixed assembly(ies), through a determined number of in-service tours, does not jeopardize the worn brake RTO capabilities of the original or the replacement wheel and brake assemblies. Since dynamometer testing is generally impractical, the applicant should forward to the FAA an in-service plan to survey wear and wear patterns from a sampling of worn in-service brakes containing steel rollers from the original manufacturer only, from the applicant only, and from an intermix brake(s).
Since the original manufacturer’s brake often contains second, and possibly third tour reground steel rotors, at least two tours of in-service evaluation with replacement steel rotors may be required to assess equivalence. This data will provide guidance for approved worn brake RTO wear limits for brakes containing replacement rotors.
15.4.8.9.5 Torque/Pressure Ratio Profiles.
A torque/pressure ratio test plan and tests are required to demonstrate equivalent gain performances over a range of test speeds and test pressures. The test article conditions, break-in conditions and procedures, test speed range, and test pressure matrix, used to evaluate both the 15-15
original and applicant wheel and brake assemblies, should be the same with tests conducted in the same order. The results of these tests will provide guidance for braking system control compatibility assessments.
15.4.8.9.6 As a minimum, the five functional landings described in paragraph 15.4.8.1 above are also a required part of this approval procedure.
15.4.8.9.7 Continued Airworthiness.
Past history with friction material couples has indicated the necessity of ongoing monitoring (by dynamometer test) of RTO capability to assure that the AFM limitations are not exceeded over the life of airplane programs. For larger transport category commercial airplanes, it has been shown that these monitoring plans have complemented the detection and correction of unacceptable deviations. The applicant should provide the FAA with a quality plan to demonstrate that the RTO capability of the friction couple is maintained with replacement steel rotors over time.
15.4.9 Auto-Braking.
The following are required for auto-braking installations based on function, non-hazard, and non-interference on airplanes for which performance without auto-braking has been determined:
15.4.9.1 The system design should be evaluated for integrity and non-hazard, including the probability and consequence of insidious failure of critical components. No single failure may compromise non-automatic braking of the airplane.
15.4.9.2 Positive indication of whether the system is operative or inoperative should be provided.
15.4.9.3 For each auto-brake setting for which approval is desired, the ground roll distance from touchdown to stop should be determined for the landing weights and altitudes within the envelope for which approval is desired. In determining ground roll distance, the performance should be established without reverse thrust, and any adverse effect upon performance associated with the use of reverse thrust should be established and accounted for. Repeatability of initial application should be shown by comparing the onset of braking for each of the range of settings. Landing ground roll distance data determined as prescribed herein should be presented in the performance information section of the AFM.
15.4.9.4 If the auto-braking system is to be approved for wet runways, auto-brake compatibility on a wet runway should be demonstrated. These tests may be limited to the highest auto-brake setting, where anti-skid activity is expected to occur throughout the stop, and a single lower setting, where anti-skid activity is expected to occur for only a portion of the stop. AFM 15-16
stopping distances for other settings can be computed based on predicted wet-runway friction coefficients and do not require demonstrations on wet runways of all auto-brake settings. Landing ground roll distance data determined on a wet runway should also be presented in the AFM for all operating modes of the system. This information is considered necessary so that the pilot can readily compare the automatic brake stopping distance and the actual runway length available, to assess the effect of the use of the automatic braking system on the runway margin provided by the factored field length.
15.4.9.5 Automatic braking systems that are to be approved for use during rejected takeoff conditions should provide only a single brake setting that provides maximum braking. In the event that automatic brakes result in a longer rejected takeoff distance than manual brakes, the AFM should present the longer rejected takeoff distance.
15.4.9.6 Procedures describing how the automatic braking system was used during the FAA evaluation and in determining the landing ground roll distance of paragraph 15.4.9.3 should be presented in the AFM.
15.4.10 Wheel Fuse Plug Integrity.
15.4.10.1 Wheel fuse plug integrity should be substantiated during braking tests where the energy level simulates the maximum landing energy. It should be demonstrated that the wheel fuse plugs will remain intact, and that unwanted releases do not occur. One acceptable method to determine this is as follows:
1. Set engine idle power or thrust at the maximum value specified (if applicable).
2. Taxi at least three miles (normal braking, at least three intermediate stops, and all engines operating).
3. Conduct accelerate-stop test at maximum landing energy, maintaining the deceleration rate consistent with the values used to determine performance distance.
4. Taxi at least three miles (normal braking, at least three intermediate stops, and all engines operating).
5. Park in an area to minimize wind effects until it is assured that fuse plug temperatures have peaked and that no plugs have released.
15.4.10.2 In lieu of simulating the maximum kinetic energy landing during an accelerate-stop test, an actual landing and quick turn-around may be performed; however, caution should be exercised in order to prevent jeopardizing the safety of the flightcrew and airplane if the wheel plugs release right after liftoff, requiring a landing to be made with some flat tires. The following elements should be included in the tests:
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1. Set engine idle power or thrust at maximum value specified (if applicable).
2. Conduct a landing stop at maximum landing energy, maintaining the deceleration rate consistent with the values used to determine stopping performance distance.
3. Taxi to the ramp (three miles minimum with normal braking, at least three intermediate stops, and all engines operating).
4. Stop at the ramp. Proceed immediately to taxi for takeoff.
5. Taxi for takeoff (three miles minimum with normal braking, at least three intermediate stops, and all engines operating).
6. Park in an area to minimize wind effects until it is assured that fuse plug temperatures have peaked and that no plugs have released.
15.4.10.3 Fuse plug protection of wheels and tires should be demonstrated to show that the fuse plugs will release when excessive energies are absorbed.
Normally, this will occur during RTO performance tests.
15.5 Skis—§ 25.737. [Reserved] 15-18
CHAPTER 16. DESIGN AND CONSTRUCTION: FLOATS AND HULLS [RESERVED] 16-1
CHAPTER 17. DESIGN AND CONSTRUCTION: PERSONNEL AND CARGO
ACCOMMODATIONS
17.1 Pilot Compartment View—§ 25.773.
17.1.1 Explanation.
[Reserved.]
17.1.2 Procedures.
For detailed guidance on complying with pilot compartment view requirements, see AC 25.773-1.
17.2 [Reserved.] 17-1
CHAPTER 18. DESIGN AND CONSTRUCTION: EMERGENCY PROVISIONS
18.1 Ditching—§ 25.801.
18.1.1 Explanation.
If certification with ditching provisions is requested, § 25.801 requires investigation of the probable behavior of the airplane in a water landing. As stated in the regulation, this investigation can be accomplished by model testing or by comparison with airplanes of similar configuration for which the ditching characteristics are known. Applicants should also demonstrate that their ditching parameters used to show compliance with §
25.801 can be attained without the use of exceptional piloting skill, alertness, or strength.
18.1.2 Procedures.
None.
18.2 Emergency Egress Assist Means and Escape Routes—§ 25.810.
18.2.1 Explanation.
18.2.1.1 Installation of slip-resistant escape route. (See §25.810(c), formerly § 25.803(e).) See AC 25-17A, § 25.803(e), for guidance regarding slip resistant material.
18.2.1.2 The effect of the slip-resistant surfaces on airplane performance, flight characteristics, and buffet should be evaluated. If there is a significant effect, this effect should be accounted for.
18.2.2 Procedures.
None.
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CHAPTER 19. DESIGN AND CONSTRUCTION: VENTILATION AND HEATING.
19.1 Ventilation—§ 25.831.
19.1.1 Explanation.
19.1.1.1 This requirement deals with minimum ventilation requirements for each occupant of the airplane, control of the ventilating air, accumulation and evacuation of smoke and harmful or hazardous concentrations of gases or vapors, and failure conditions of the ventilation system. Specific quantities of fresh air along with carbon monoxide and carbon dioxide concentration limits are specified in the rule. AC 25-20 provides guidance for methods of showing compliance with the ventilation requirements. Reference should also be made to paragraphs 29.1 and 31.2 of this AC dealing with § 25.1121, Exhaust systems, and § 25.1197, Fire extinguishing agents, respectively.
19.1.1.2 The objective of the inflight smoke evacuation test is to confirm that the flightcrew emergency procedures and the ventilation system are capable of handling heavy smoke, and to show that when using the emergency procedures, the smoke will dissipate at a reasonable rate. This is a quantitative and qualitative evaluation.
19.1.2 Procedures.
19.1.2.1 Flight testing should be conducted to ensure the amount of ventilation air provided meets the requirements specified and the flightcrew is able to accomplish their duties without undue fatigue and discomfort. Ventilation system controls in the flight deck should be demonstrated to perform their intended function.
19.1.2.2 The passenger and crew compartment should be monitored for the presence of carbon monoxide. Various flight and equipment configurations should be tested. A carbon monoxide test kit is normally used for this evaluation.
19.1.2.3 Inflight smoke evacuation testing should be conducted in accordance with AC 25-9A.
19.2 Cabin Ozone Concentration—§ 25.832. [Reserved]
19.3 Combustion Heating Systems—§ 25.833. [Reserved] 19-1
CHAPTER 20. DESIGN AND CONSTRUCTION: PRESSURIZATION
20.1 Pressurized Cabins—§ 25.841.
20.1.1 Explanation.
20.1.1.1 Section 25.841(a) specifies cabin pressure altitude limits, as a function of the external pressure altitude, for cabins and compartments intended to be occupied. AC 25-20 provides additional guidance for pressurized cabins.
These cabin pressure altitude limits, to be demonstrated by flight testing, are:
20.1.1.1.1 Not more than 8,000 feet, at the maximum operating altitude of the airplane, for normal operation of the pressurization system.
20.1.1.1.2 For airplanes to be operated above 25,000 feet, the airplane must be able to maintain a cabin pressure altitude of not more than 15,000 feet in the event of any reasonably probable failure or malfunction in the pressurization system.
20.1.1.2 The 8,000-foot limit on cabin pressure altitude applies during normal operations at all altitudes, up to the maximum operating altitude of the airplane. For airplanes operating at airports with altitudes higher than 8,000 feet (see paragraph 20.1.1.3), an equivalent level of safety finding must be made in accordance with § 21.21(b)(1) to allow the higher than 8,000-foot cabin pressure altitude needed for these operations.
20.1.1.3 Though not addressed by § 25.841, airplanes may incorporate a “high altitude mode” to permit takeoff and landing at airports above 8,000 feet.
For takeoff and landing altitudes above 8,000 feet, the cabin pressure limits to be demonstrated by flight testing are:
20.1.1.3.1 Prior to beginning a descent into a high-altitude airport, not more than 8,000 feet.
20.1.1.3.2 During a descent into or climb out of a high-altitude airport, not more than 15,000 feet.
20.1.1.3.3 After a takeoff from a high-altitude airport and after the cabin pressure altitude decreases to 8,000 feet, not more than 8,000 feet.
20.1.1.4 Section 25.841(b)(6) requires an aural or visual warning to the flightcrew when the cabin pressure altitude exceeds 10,000 feet. The intent of this requirement is to warn the crew when a safe or preset cabin pressure altitude limit is exceeded. However, complying with this regulation when operating at airports with altitudes higher than 10,000 feet (see paragraph 20.1.1.3) would result in nuisance cabin pressure warnings. For 20-1
systems that set the cabin pressure altitude warning limit above 10,000 feet for operations at high altitude airports, an equivalent level of safety finding must be made in accordance with § 21.21(b)(1).
20.1.2 Procedures.
It is recommended that the test airplane have the maximum allowable leakage rate permitted by the type design specifications. If an airplane does not meet this criterion, it will be necessary to substantiate compliance by additional testing or analysis for the maximum leakage rate allowed by the type design.
20.1.2.1 Normal Operating Conditions—8,000-Foot Cabin Pressure Altitude.
20.1.2.1.1 With the pressurization system operating in its normal mode, verify that the cabin pressure altitude does not exceed 8,000 feet during climb, cruise, or descent at any altitude up to and including the maximum operating altitude for which the airplane is to be certificated.
20.1.2.1.2 A stable condition should be held long enough to record any cyclic fluctuations in cabin pressure due to relief valve operation.
20.1.2.2 Failure Conditions—15,000-Foot Cabin Pressure Altitude.
20.1.2.2.1 The critical probable system failure condition should be identified. The cabin pressure altitude warning system should be set to the high-altitude side of its tolerance band or additional testing or analysis may be necessary for compliance. If more than one system failure mode is determined to meet the “probable failure condition” criterion, the flight test should be conducted for each failure mode identified.
20.1.2.2.2 The airplane should be stabilized in the cruise configuration at the maximum operating altitude it is to be certificated to, with the pressurization system operating in its normal mode.
20.1.2.2.3 After initiating the critical failure to allow the cabin pressure altitude to increase, the flight test crew should immediately don their oxygen masks but take no further corrective action until 17 seconds after the 10,000-foot cabin pressure altitude warning activates. Emergency descent procedures should then be initiated and the descent continued to an altitude below 15,000 feet.
20.1.2.2.4 The cabin pressure altitude should not exceed 15,000 feet at any time during the test.
20.1.2.3 High Altitude Takeoff Conditions (Greater than 8,000 Feet).
20.1.2.3.1 The pressurization system should be placed in its high-altitude mode. It may be necessary to configure the oxygen system to prevent deployment of the oxygen masks at 10,000 feet, if the system is so designed. AFM 20-2
procedures may need to be developed. The same applies to high altitude landings above 10,000 feet.
20.1.2.3.2 The cabin pressure altitude should not exceed the maximum allowable takeoff and landing altitude (within an acceptable tolerance) during an actual climb-out from a high-altitude airport to the maximum operating altitude the airplane is to be certificated for, or during an inflight simulation of such a climb-out. The simulation should commence the climb, from a starting altitude of 8,000 feet or more, with the airplane unpressurized.
20.1.2.3.3 The cabin pressure altitude should eventually decrease to 8,000 feet and then not exceed 8,000 feet for the duration of the test.
20.1.2.4 High Altitude Landing Conditions (Greater than 8,000 Feet).
20.1.2.4.1 The airplane should be stabilized in the cruise configuration prior to beginning a descent.
20.1.2.4.2 The pressurization system should be placed in its high-altitude mode.
20.1.2.4.3 The cabin pressure altitude should not exceed the maximum allowable takeoff and landing altitude (within an acceptable tolerance) during the descent to an actual, or simulated, landing at a high-altitude airport.
20.2 Tests for Pressurized Cabins—§ 25.843.
20.2.1 Explanation.
20.2.1.1 Section 25.843(b)(3) requires flight testing to evaluate the performance of the pressurization system and all related sub-systems at maximum altitude and under the dynamic conditions of climbing and descending flight. This testing substantiates the ability of the pressurization system to function correctly in stable and dynamic external pressure conditions.
20.2.1.2 Section 25.843(b)(4) requires an investigation of the functionality of all doors and emergency exits after the flight test required by § 25.843(b)(3).
The concern is the potential for jamming caused by the variable relative positions of doors and fuselage structure during the pressurization/depressurization cycle.
20.2.2 Procedures.
The following tests may be initiated from an airport at any altitude within the airplane’s proposed takeoff limitations. The pressurization system should be operated in its normal mode. MMEL dispatch may be taken into consideration and additional testing required to verify MMEL configuration.
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