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strength under reasonable service conditions. When a fabrication process requires close control to attain this objective, the process shall be performed in accordance with a process specification.

Protection. All members of the primary structure shall be suitably protected against deterioration or loss of strength in service due to weathering corrosion, abrasion, or other causes. In seaplanes special precautions shall be taken against corrosion from salt water, particularly where parts made from different metals are in close proximity. Adequate provisions for ventilation and drainage shall be made. Inspection Provisions. Adequate means shall be provided to permit the examination of such parts of the airplane as require periodic inspection.

Major Components

Wings

Proof of Strength. The strength of stressed-skin wings shall be substantiated by load tests or by combined structural analysis and tests.

External Bracing. When wires are used for external lift bracing, the structure shall be designed to develop at least one half the required load factor, with any one wire cut. Rigging loads shall be taken into account in a rational or conservative manner. When brace struts of large fineness ratio are used, the aerodynamic forces on such struts shall be taken into account.

Ribs. The strength of ribs shall be proved by test to at least 125 percent of the ultimate loads for the most severe loading conditions, unless a rational analysis and test procedure is employed. The load shall be suitably distributed between upper and lower wing surfaces unless a more severe distribution is used. The effects of ailerons and high-lift devices shall be properly accounted for. Rib tests shall simulate conditions in the airplane with respect to torsional rigidity of spars, fixity conditions, lateral support and attachment to spars.

Covering. Proof of strength of fabric covering is not required when standard grades of cloth and methods of attaching and doping are employed, provided however, that special tests may be required when it appears necessary to account for the effects of unusually high design airspeeds or slipstream velocities or similar factors.

Control Surfaces (Fixed and Movable)

Proof of Strength. Limit load tests are required to prove compliance with limit load requirements. Control surface tests shall include the horn or fitting to which the control system is attached. Analysis or individual load tests shall be conducted to demonstrate compliance with the multiplying factor of safety requirements for control surface hinges. Rigging loads due to wire bracing shall be taken into account in a rational or conservative manner.

Installation. Movable tail surfaces shall be so installed that there is no interference between the surfaces or their

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bracing when any one is held in its extreme position and any other is operated through its full angular movement.

Hinges Hinges of the strap type bearing directly on torque tubes are permissible only in the case of steel torque tubes which have a multiplying factor of safety at the hinge point of not less than 1.5. Control surface hinges, excepting ball and roller bearings, shall incorporate a multiplying factor of safety of not less than 6.67 with respect to the nitimate bearing strength of the softest material used as a bearing.

Hinges incorporating bal or roller bearings shall be designed to not exceed the manufacturer's non-Brinell rating at limit load.

Control SystemS

General. All controis shall operate with suficient ease. smoothness and positiveness to permit the proper performance of their function and shall be so located and identified as to provide the greatest possible convenience in operation and the least possibility of confusion and consequent inadvertent operation. Wherever possible, the sense of motion involved in the operation of the control shall correspond with the sense of the effect of the operation upon the airplace or the part operated, or failing this, shal suggest it. Primary Fight Controis. The primary fight controls shall consist of a control stick directly in front of each pilot or a column providing a grip or wheel in that position. and. when the rudder is independently controlled, à pair of foot pedals or a rudder bar for each pilot. The primary controls shail operate as follows:

a A rearward displacement of the top of the stick, grip, or wheel shall cause the airplane to pitch nose up.

b A displacement of the stick or grip toward the right or a right hand rotational displacement of the wheel shall be required to bank the airplane right wing down.

A forward displacement of the right hand rudder pedal shall be required to turn the airplane to the right.

Trimming Controis. The trimming controis shall be convenientiv grouped and each shall operate in the plane and with the sense of the motion of the airplane which their operation is intended to produce. Proper precautions shall be taken against the possibility of inadvertent or abrupt tab operation. Means shall be provided to indicate to the pilot the range of adjustment and the direction of motion. Tab controis shall be irreversible. nondexible and extremely

gged, unless the tab is properly balanced about its hinge ine. Trimming devices shall be capable of continued normai operation in spite of the failure of any one connecting or transmitting element in the primary fight control system.

Wing Flap Controls. Wing dap controis shall be so oriented and shall operate in such manner as to require an upward motion of the control to retract the daps. The controis shail maintain, without assistance from the crew.

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any desired flap position. Means shall be provided to indicate the flap position to the pilot.

The flap-operating mechanism shall be such as to prevent sudden inadvertent or automatic opening of the flap at speeds above the design speeds of the extended flap conditions. The time required to extend fully or to retract flaps shall not be less than 15 seconds unless it can be demonstrated that the operation of the flaps in a lesser time does not result in unsatisfactory flight characteristics.

For transport category airplanes. the flap control shall provide means for bringing the flaps from any position within the operating range to any one of three positions. designated hereinafter as landing, approach, and take-off positions, or to the fully retracted position. by placing the primary flap control in a single setting marked as corre sponding to each such flap position, the flaps thereupon moving directly to the desired position without requiring further attention. If any extension of the flaps beyond the landing position is possible, the flap control shall be clearly marked to identify such range of extension.

The landing position, approach position, and take-off position, or any of them, may be made variable with altitude or weight by means of a secondary flap control provided for that purpose. Such a secondary control, if provided, shall operate independently of the primary control and in such manner that when it has been adjusted (for the effect of weight or altitude), the necessary flap position can thereafter be obtained by placing the primary flap control in the desired position. The secondary control shall be so designed and marked as to be readily operable by the crew.

The rate of flap retraction shall be such as to permit compliance with 2.131 (b).

Operation Test. An operation test shall be conducted by operating the controls from the pilot's compartment with the entire system so loaded as to correspond to the minimum limit control force specified for the control system in question. In this test there shall be no jamming, excessive friction, or excessive deflection.

Installation. All control systems and operating devices shall be so designed and installed as to prevent jamming, chafing, interference by cargo, passengers or loose objects. and the slapping of cables or tubes against parts of the airplane. All pulleys shall be provided with satisfactory guards.

Stops. All control systems shall be provided with stops which positively limit the range of motion of the control surfaces. Stops shall be capable of withstanding the loads corresponding to the design conditions for the control system and shall minimize deflection of the surfaces or the controls beyond their design limits.

Power Operated Flight Controls. When a power device is used for operating the primary flight controls provisions shall be made for retaining sufficient control for steady flight and landing after failure of any single part of the system,

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excluding failures in mechanical parts of the system comparable to equivalent parts of manually operated systems. NOTE: One way of meeting this requirement would be to insure that the pilot has sufficient mantal control after failure of the power system. Another way would be to provide at least two entirely independent power systems. Provision shall be made for all foreseeable kinds of failure so as to insure that any control circuits rendered inoperative and or incperable by the falled power system can quickly be put into a position for safe high aŭ moderate speeds. These requirements shall be met under the conditions of fallure of all engines in single and twin-engined airplanes, and of any two engines in other multiengined airplanes.

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Control System Locks. When a device is provided for loesing a control surface while the airerait is on the ground or water, compliance with the following requirements shall be shown

a The locking device shall be so installed as to prevent taxing the strerait from taking of while the ces is engaged. b. Means shall be provided to precinde the possiblity of any lock becoming engaged during tights.

Landing Gear

Shock Absorption. Main, nose, and tail wheel zits shall incerperste shock seserving elements whose adequacy demonstrated by the tests specited in Section 22411." In sddition, the seces abserving ability of the landing gear in taxing wrist be demonstrated in the operational test of 2:43.

Retruring Mechanism and Supports. The stricture supporting the landing rear in its retracted position shall be designed for the maximum cad factors in the dient eccdtons. The retracting mechanism and supporting stricture shall be designed for the combination of fretien, inertia. brake torque, and air-irag cats occurring firing retraction at any sirspeed and cad faeter up to these specified for the faps extended condition. 2212 Means shall be provided for the purpose of maintaining the wheels in the extended

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2.31420 Emergency Gneration. When other than manual operszon of the landing rear is employed, an auxitary means of extending the landing gear shall be providei.

231421 Cheration Test. Proper functioning of the landing rear petrseting mechanism under the speeded imit retracting loads shall be lemonstrated by operation tests.

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Pisition Indictor and Wirniad Zeres. When react soie landing wheels are used, visual means shall be provided for indiesting to the pilot, at all times the position of each of the wheels. I semicon, andpianes shall be provided with an aurai warning levies vaien stad finetion continuJusty when the engines hottied preparatory to landing, unni extension is completed and the gear is locked. For Jiner than Tansport bategory sirvianes, any other eq tally

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effective warning device may be substituted in lieu of an aural device.

Retraction Control. The control provided for retractable gears shall be so oriented and shall operate in such a manner as to require an upward motion of the control to retract the gear.

Wheels. Main landing gear wheels (i. e. those nearest the airplane center of gravity) shall be of an approved type in accordance with Part 5.1. The rated static load of each main wheel shall not be less than the design weight for ground loads (2.240 and 2.240-T) divided by the number of main wheels. Nose wheels shall be approved in accordance with Part 5 for an ultimate radial load not less than the maximum nose wheel ultimate loads obtained in the ground loads requirement, 2.24, and for the corresponding side and burst loads specified in Part 5.1.

Tires. A landing gear wheel may be equipped with any type of tire constructed by a reputable maker provided that the rating of the maker is not exceeded. When specially constructed tires are used to support an airplane, the wheels shall be plainly and conspicuously marked to that effect. Such markings shall include the make, size, number of plies and identification marking of the proper tire.

Brakes. Transport category airplanes shall be equipped with brakes certificated in accordance with the provisions. of Part 5 for the maximum certificated landing weight at sea level and the power-off stalling speed. The brake system for such airplanes shall be so designed and constructed that in the event of a single failure in any connecting or transmitting element in the brake system, (exclusive of the brake operating handle or pedal and the primary braking elements such as the drum and shoe or their equivalent) or the loss of any single source of hydraulic or other brake operating energy supply, it shall be possible, as shown by suitable test or other data, to bring the airplane to rest under the conditions specified in 2.124-T with a mean negative acceleration during the landing roll of at least 50 percent of that obtained in determining the landing distance under that section.

Hulls and Floats

Buoyancy (Main Seaplane Floats). Main seaplane floats shall have a buoyancy in excess of that required to support the gross weight of the airplane in fresh water as follows:

(a) 80 percent in the case of single floats.
(b) 90 percent in the case of double floats.

Main seaplane floats for use on aircraft of 2,500 pounds (1,134 kg.) or more maximum authorized weight shall contain at least five water-tight compartments of approximately equal volume. Main seaplane floats for use on aircraft of less than 2,500 pounds (1,134 kg.) maximum authorized weight shall contain at least four such compartments.

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