for substantiating replacement or modified brake installations and may be applied to approved brakes of any manufacturer. The replacement brake does not have to be manufactured by the maker of the original brake.

(2) Brakes which have been approved under TSO or preceding approval standards (whichever is pertinent) may be approved as a replacement brake on an existing airplane type upon the presentation of test reports and other pertinent computations showing:

(i) That, insofar as deceleration performance is concerned, the replacement or modified brakes are equal to or better than the original brake installation on the basis of dynamometer tests contained in this section, and

(ii) That, the replacement or modified brakes, when installed on the airplane, comply with the ground handling requirements of § 4b.170.

(b) Brake modifications. Modifications to a previously approved wheelbrake installation involving changes to component parts which will involve variations in kinetic energy absorption characteristics should be subjected to the dynamometer tests contained in subparagraph (1) of this paragraph in addition to the dynamometer tests specified in paragraphs (e) and (f) of this section for the accelerate-stop and landing conditions and should also include a check of operating and ground handling characteristics. Typical modifications which vary the kinetic energy absorption characteristics are as follows: changes of brake lining material, changes in brake discs or brake drum material, reductions in friction surface plan dimensions (area), etc.

(1) The minimum reliability standards for brakes referenced in TSO-C26 and contained in Specification AS227A should be used as a guide for modified brakes. However, section 5.4.3 of AS227A may be applied as follows for evaluating such modifications:

(1) Thirty tests simulating the stopping of an airplane at 100 percent kinetic energy.

(ii) One test simulating the stopping of an airplane at 125 percent kinetic energy.

(c) Determination of kinetic energy requirements. (1) In the case of replacement brakes (that is, those brakes

K. E.= the maximum kinetic energy as deWV termined from the most critical combination of weight and speed (in terms of ground speed). In determining the maximum speed, the effects of tailwind, altitude and flap setting should be taken into account.

K. E.= the kinetic energy absorbed by AD aerodynamic drag of the airplane during the deceleration portion of the accelerate-stop and landing runs. This kinetic energy should be determined from available test data of the airplane or by other reliable calculations based on the basic parameters for the type of airplane involved.

(2) In the case of brakes modified as described in paragraph (b) of this section, the kinetic energy to be absorbed on the dynamometer should be determined in accordance with the following formula:

(3) Brake lining should not be run-in to a degree which would be greater than the run-in for new lining when installed on an airplane prior to being put in regular airline service.

(4) Due to wing-lift acting on the airplane, the dynamometer tests should account for tire rolling friction due to the differential in braking effect resulting from the varying rolling radius of the tire on the runway as compared to the constant tire radius at constant tire deflection which occurs throughout the entire dynamometer run.

(5) The dynamometer mass should be corrected so that the selected inertia equivalent (I. E.) will result in a correct or conservative kinetic energy test value.

(6) During dynamometer testing a variable brake pressure, which does not exceed that pressure which is available from the airplane brake system intended for use with the replacement brake, should be used in duplicating as nearly as practicable the original torque-speed and velocity-time flight test data corrected for aerodynamic drag and tire rolling friction.

airplane

test.

(e) Accelerate-stop distance This condition is normally the most critical from a kinetic energy standpoint. The original flight test accelerate-stop deceleration camera data obtained during the type certification tests of the airplane should be obtained and corrected for aerodynamic drag and tire rolling friction.

(1) Continuous records of dynamometer torque-speed or velocity-time data for at least three of the runs, when absorbing the required kinetic energy for the critical combination of take-off weight and V1 speed, should duplicate, as nearly as practical, the original airplane brake deceleration data. These dynamometer records should be converted to corrected and faired velocity versus distance values and be plotted and superimposed on the curve for the original airplane velocity-distance data, and

(2) The average of the above three corrected dynamometer velocity-distance curves should be superimposed on the curve for the original airplane velocity-distance data.

(3) The curves plotted in subparagraphs (1) and (2) of this paragraph should compare favorably with the original corrected flight data over the entire speed range and should indicate that,

from any given speed, the airplane stopping distance would be equal to or less than the distance resulting from the original brake installation at the required kinetic energy level corresponding to the actual accelerate-stop conditions which prevailed during the airplane type certification tests.

(4) If, in compliance with subparagraph (1) of this paragraph, velocitytime data are submitted in lieu of torquespeed data, then sufficient spot-check calculations of the velocity-time data should be made to insure an accuracy comparable to the accuracy of torquespeed data. Inasmuch as torque-speed data are useful for airplane modification and design purposes, it is desirable that comparable and complete torque-speed data be included in the data submitted.

(5) Dynamometer time history recordings of brake pressure, torque, speed, and calculations for aerodynamic drag, tire rolling friction, and dynamometer mass correction, and all pertinent airplane data, should be submitted, together with an analysis showing the detailed calculations and charts necessary to establish the speed-distance relationship and comparison with the original airplane deceleration test data.

(f) Landing distance test. In order to substantiate landing distances, at least three dynamometer runs, using the critical combinations of landing weight and contact speed, should be conducted on the same brake unit. Landing distance data, compiled in accordance with the method described in paragraph (e) of this section for accelerate-stop evaluation, should be submitted. The landing distance data, which are comparable to those of paragraph (e) of this section for the accelerate-stop data, should compare favorably with the corrected airplane flight test results obtained with the original brakes in order to substantiate the adequacy of the replacement brakes, insofar as landing distances are concerned.

(g) Aircraft functional tests. The brakes should be tested on the airplane to determine their functional characteristics as indicated in paragraph (a) (2) of this section. Functioning characteristics should be observed during taxi and engine runup conditions and at least three normal take-offs and landings, at the maximum landing weight, should be conducted. During these tests, the

brakes should be checked for any undesirable characteristics such as "grabbing," "fading," etc., and should at least be visually inspected, without dismantling, at the completion of the test in order to determine any evidence of malfunction or failure. If no malfunctioning has occurred, this visual inspection is adequate, but if malfunctioning does occur, a thorough inspection should be conducted. If any characteristics arise which indicate that stopping distances would exceed the original values in the FAA Approved Airplane Flight Manual, then the Administrator may require actual camera recorded airplane deceleration tests or any other tests deemed necessary to establish the adequacy of the brakes.

[Supp. 24, 19 F. R. 4461, July 20, 1954]

§ 4b.337-4 Antiskid devices and installations (FAA policies which apply to § 4b.337).

(a) Eligibility. Antiskid devices meeting the airworthiness portions of Military Specification MIL-B-8075 (ASG) and any amendments' thereto, are acceptable for installation on civil aircraft. Requests for deviations from these specifications should be submitted to the FAA Regional Office, Aircraft Engineering Division. The installation of the antiskid device should comply with the requirements specified in paragraph (b) of this section. The antiskid device and its installation will be approved for use on civil aircraft when the tests specified in paragraph (c) of this section have been satisfactorily demonstrated.

(b) Installation-(1) Data required. An engineering evaluation of the antiskid installation as installed on the airplane, including all necessary components, should be conducted. This analysis and complete descriptive data should be submitted to the FAA. The data should include hydraulic and electric schematic diagrams of the installation, assembly drawings of antiskid system units, test results or stress analysis substantiating structural strength of attachments and modification of the axle or other structural members, installation drawings, recommended instructions pertaining to installation, maintenance and operation and analysis of flight test data and results. Schematic drawings

Proposed amendments may be obtained from the Federal Aviation Agency, Washington 25, D.C.

should refer to all units in the normal and emergency brake systems. The engineering evaluation should also assure that the antiskid system does not cause undesirable and adverse yaw characteristics.

(i) Engineering evaluation should account for a bounce condition wherein the wheels may leave the runway after the brakes have been applied; for a condition wherein the wheels stay on the runway but the oleos are extended (if the system utilizes landing gear oleo compression in its operation) and for a condition in which the wheels of one main gear may not be in contact with the runway for a considerable time while the wheels of the other main gear are firmly on the runway. If the antiskid installation incorporates the "landing with brake pedals depressed" feature, then this type of operation should also be considered.

(ii) It should be shown that the brake cycling frequency imposed by the antiskid installation will not result in excessive loads on the landing gear because of proximity to resonant landing gear frequencies.

(2) Systems. The entire brake system (including both the basic brake system and the antiskid system) should conform to § 4b.337. The single failure criterion of § 4b.337 should be extended to include the antiskid system.

(i) In the event of a probable malfunction within the antiskid system which would result in loss of the antiskid feature in one or more brake units, those brake units affected should automatically revert to normal braking.

(ii) [Reserved]

(iii) A means should be provided so that the pilot or copilot can readily deactivate the antiskid system. For simple mechanical type antiskid installations wherein any single probable malfunction is considered remote and which will render only one braked wheel inoperative insofar as antiskid operation is concerned, the deactivating means need not be located in the cockpit.

(iv) Antiskid installations should not cause surge pressures in the brake hydraulic system which would be detrimental to either the normal or emergency brake system and components.

(v) The antiskid equipment should insure satisfactory operation on slippery runways as well as on dry hard surfaced

runways without additional antiskid adjustment.

(c) Tests and analyses. (1) When an antiskid system is included as original equipment on an airplane, it is not required that field length data,' with antiskid inoperative, be determined.

(2) Tests and analyses for the approval of an antiskid system to be used with a previously approved brake installation, without consideration for reduction of runway distances, should be conducted in accordance with this paragraph. When equivalent alternate procedures are developed and approved, they may be used in lieu of the method specified in this paragraph. If credit for shorter field lengths is requested on the basis of an antiskid installation, then complete flight tests should be conducted in accordance with §§ 4b.115, 4b.122, 4b.123, 4b.170 and 4b.171.

(3) When an antiskid system is installed, the braking performance and airplane stopping distances should be at least equivalent to those obtained during the accelerate-stop and landing type certification tests. The tests to be conducted are based on the high speed condition as being critical, both for airplane braking as controlled by the antiskid system, and for the functional integrity of an acceptable antiskid device. However, should it become necessary for a particular type of installation, these tests may be modified as warranted.

(i) Conduct at least one acceleratestop test at each of the following speeds: 80, 90, and 100 percent of the highest V1 speed for which the airplane is certificated. The maximum landing weight, or the lowest weight above maximum landing weight necessary to keep the airplane from leaving the runway at the highest V1 speed, should be used in the above three tests. When appropriate, the decelerate portions of the acceleratestop tests may be demonstrated by landings with wing flaps in takeoff position in lieu of accelerating the airplane to V1 speed on the runway. (See also § 4b.115-1.)

(ii) Conduct at least one landing deceleration test at each of the following weights: maximum landing weight, an

It is desirable to determine field length data with the antiskid inoperative in order that airplane operation may be conducted with antiskid inoperative if so desired by the operator.

intermediate landing weight and normal minimum landing weight. All landings should be made from the highest corresponding contact speeds used in determining FAA Approved Airplane Flight Manual field lengths.

(4) Conduct controllability tests in accordance with §§ 4b.170 and 4b.171 (except for the emergency braking condition) after the occurrence of any single malfunction within the antiskid system (excluding the device and those components which were determined to be satisfactory based on laboratory tests). Single probable malfunctions, which analysis indicates may be likely to occur, should be simulated during landing or simulated landing deceleration tests. If analysis shows clearly that a particular malfunction would not adversely affect controllability, that malfunction need not be simulated in flight tests.

(5) Conduct taxi tests to demonstrate that repeated rapid full brake pedal application and release does not result in excessive delay in brake reapplications and that ground handling maneuvering characteristics and sensitivity of braking effect are satisfactory.

(6) Conduct tests and analyses to determine the effect of automatic cyclic brake action on the emergency brake system fluid supply. The fluid volume (reserved for emergency use in the reservoir or emergency accumulators of the basic brake system) may be adequate for manual braking but may be adversely affected by an antiskid installation. Hence, an engineering evaluation should be conducted to show that the antiskid

In order to assure stopping distances equivalent to those shown in the Airplane Flight Manual, camera recording, or equivalent recordation methods should be used. To ascertain that the measured stopping distances are equivalent to those in the Airplane Flight Manual it will be necessary to compare the measured antiskid data with the data obtained during the manufacturer's original certification tests for the weight used in the antiskid tests at the highest speed for that weight shown in the Airplane Flight Manual.

If it can be shown by the accelerate-stop distance tests conducted and the data obtained in subdivision (1) of this subparagraph that the landing distances when using normal landing braking techniques, would not exceed the landing distances approved without antiskid devices, then the landing distance tests specified in subdivision (ii) of this subparagraph need not be conducted.

system will not have an adverse effect on braking when the airplane is stopped by means of the emergency brake system, or to show that the antiskid system is automatically made inoperative when emergency braking is used.

(7) If, during the tests specified in this paragraph, adjustments or modifications to the antiskid device or its installation proved necessary and indicated the possibility of encountering unreliable operation due to maintenance difficulties or the need for frequent adjustments, then accelerated service functioning and reliability tests should be conducted as deemed necessary.

[Supp. 28, 21 F.R. 2558, Apr. 19, 1956, as amended by Supp. 37, 23 F.R. 2789, Apr. 26, 1958]

(and wheel tires, if used) will provide a sufficient margin of positive stability to minimize capsizing in rough fresh water.

(b) For the purpose of communication between compartments, bulkheads with watertight doors shall be allowed. [15 F. R. 3543, June 8, 1950, as amended by Amdt. 4b-6, 17 F. R. 1093, Feb. 5, 1952] PERSONNEL AND CARGO ACCOMMODATIONS § 4b.350 Pilot compartment; general.

All references to flight crew in this section and §§ 4b.351 through 4b.353 shall mean the minimum flight crew established in accordance with § 4b.720.

(a) The arrangement of the pilot compartment and its appurtenances shall provide safety and assurance that the flight crew will be able to perform all of their duties and operate the controls in the correct manner without unreasonable concentration and fatigue.

(b) The primary flight controls listed on figure 4b-16, excluding cables and control rods, shall be so located with respect to the propellers that no portion of the flight crew or the controls lies in the region between the plane of rotation of any inboard propeller and the surface generated by a line passing through the center of the propeller hub and making an angle of 5° forward or aft of the plane of rotation of the propeller.