axes. The propulsion is independent of the rotor system and usually consists of conventional propellers.

(c) General design—(1) Standard atmosphere. The standard atmosphere is an atmosphere (see NACA Technical Report 1235) defined as follows:

(i) The air is a dry, perfect gas,

(ii) The temperature at sea level is 59° F.,

(iii) The pressure at sea level is 29.92 inches Hg,

(iv) The temperature gradient from sea level to the altitude at which the temperature equals -69.7° F. is -0.003566° F./ft. and zero thereabove, and

(v) The density Po at sea level under the above conditions is 0.002377 pound sec2/ft'.

(2) Maximum anticipated air temperature. The maximum anticipated air temperature is a temperature specified for the purpose of compliance with the standards. (See powerplant cooling § 6.451.)

(3) Aerodynamic coefficients. Aerodynamic coefficients are nondimensional coefficients for forces and moments. They correspond with those adopted by the National Aeronautics and Space Administration (formerly the National Advisory Committee for Aeronautics).

(4) Autorotation. Autorotation is a rotorcraft flight condition in which the lifting rotor is driven entirely by the action of the air when the rotorcraft is in motion.

(5) Autorotative landing. An autorotative landing is any landing of a rotorcraft in which the entire maneuver is accomplished without the application of power to the rotor.

(6) Ground resonance. Ground resonance is the mechanical instability encountered when the rotorcraft is in contact with the ground.

(7) Mechanical instability. Mechanical instability is an unstable resonant condition due to the interaction between the rotor blades and the rotorcraft structure while the rotorcraft is on the ground or airborne.

(d) Weights-(1) Maximum weight. The maximum weight of the rotorcraft is that maximum at which compliance with the requirements of this part is demonstrated. (See 6.101.)

(2) Minimum weight. The minimum weight of the rotorcraft is that minimum at which compliance with the requirements of this part is demonstrated. (See § 6.101.)

(3) Empty weight. The empty weight of the rotorcraft is a readily reproducible weight which is used in the determination of the operating weights. (See

§ 6.104.)

(4) Design maximum weight. The design maximum weight is the maximum weight of the rotorcraft at which compliance is shown with the structural loading conditions. (See § 6.101.)

(5) Design minimum weight. The design minimum weight is the minimum weight of the rotorcraft at which compliance is shown with the structural loading conditions. (See § 6.101.)

(6) Design unit weight. The design unit weight is a representative weight used to show compliance with the structural design requirements:

(i) Gasoline 6 pounds per U. S. gallon. (ii) Lubricating oil 7.5 pounds per U. S. gallon.

(iii) Crew and passengers 170 pounds per person.

(e) Speeds-(1) IAS. Indicated air speed is equal to the pitot static airspeed indicator reading as installed in the rotorcraft without correction for air-speed indicator system errors but including the sea level standard adiabatic compressible flow correction. (This latter correction is included in the calibration of the air-speed instrument dials.) (See §§ 6.612 and 6.732.)

(2) CAS. Calibrated air speed is equal to the air-speed indicator reading corrected for position and instrument error. (As a result of the sea level adiabatic compressible flow correction to the air-speed instrument dial, CAS is equal to the true air speed TAS in standard atmosphere at sea level.)

(3) EAS. Equivalent air speed is equal to the air-speed indicator reading corrected for position error, instrument error, and for adiabatic compressible flow for the particular altitude. (EAS is equal to CAS at sea level in standard atmosphere.)

(4) TAS. True air speed of the rotorcraft relative to undisturbed air. (TAS EAS (po/p) 1/2)

(5) VH. The maximum speed obtainable in level flight with rated rpm and power.

(7) Vx. The speed for best angle of climb.

(8) Vr. The speed for best rate of climb.

(f) Structural—(1) Limit load. A limit load is the maximum load anticipated in normal conditions of operation. (See § 6.200.)

(2) Ultimate load. An ultimate load is a limit load multiplied by the appropriate factor of safety. (See §6.200.)

(3) Factor of safety. The factor of safety is a design factor used to provide for the possibility of loads greater than those anticipated in normal conditions of operation and for uncertainties in design. (See § 6.200.)

(4) Load factor. The load factor is the ratio of a specified load to the total weight of the rotorcraft; the specified load may be expressed in terms of any of the following: aerodynamic forces, inertia forces, or ground or water reactions.

(5) Limit load factor. The limit load factor is the load factor corresponding with limit loads.

(6) Ultimate load factor. The ultimate load factor is the load factor corresponding with ultimate loads.

(7) Fitting. A fitting is a part or terminal used to join one structural member to another. (See § 6.307 (d).)

(g) Powerplant installation 1 — (1) Brake horsepower. Brake horsepower is the power delivered at the propeller shaft of the engine.

(2) Take-off power or thrust. (i) Take-off power for reciprocating engines is the brake horsepower developed under standard sea level conditions, under the maximum conditions of crankshaft rotational speed and engine manifold pressure approved for the normal takeoff, and limited in use to a maximum continuous period as indicated in the approved engine specification.

(ii) Take-off power for turbine engines is the brake horsepower developed under static conditions at specified altitudes and atmospheric temperatures, under the maximum conditions of engine rotor shaft rotational speed and gas temperature approved for normal take

1 For engine airworthiness requirements see Part 13 of this subchapter.

off, and limited in use to a maximum continuous period as indicated in the approved engine specification.

(iii) Take-off thrust for turbine engines is the jet thrust developed under static conditions at specified altitudes and atmospheric temperatures, under the maximum conditions of engine rotor shaft rotational speed and gas temperature approved for the normal take-off, and limited in use to a maximum continuous period as indicated in the approved engine specification.

(3) Maximum continuous power or thrust. (i) Maximum continuous power for reciprocating engines is the brake horsepower developed in standard atmosphere at a specified altitude, under the maximum conditions of crankshaft rotational speed and engine manifold pressure, and approved for use during periods of unrestricted duration.

(ii) Maximum continuous power for turbine engines is the brake horsepower developed at specified altitudes, atmospheric temperatures, and flight speeds, under the maximum conditions of engine rotor shaft rotational speed and gas temperature, and approved for use during periods of unrestricted duration.

(iii) Maximum continuous thrust for turbine engines is the jet thrust developed at specified altitudes, atmospheric temperatures, and flight speeds, under the maximum conditions of engine rotor shaft rotational speed and gas temperature, and approved for use during periods of unrestricted duration.

(4) Gas temperature. Gas temperature for turbine engines is the temperature of the gas stream obtained as indicated in the approved engine specification.

(5) Manifold pressure. Manifold pressure is the absolute pressure measured at the appropriate point in the induction system, usually in inches of mercury.

(6) Critical altitude. The critical altitude is the maximum altitude at which in standard atmosphere it is possible to maintain, at a specified rotational speed, a specified power or a specified manifold pressure. Unless otherwise stated, the critical altitude is the maximum altitude at which it is possible to maintain, at the maximum continuous rotational speed, one of the following:

(i) The maximum continuous power, in the case of engines for which this

power rating is the same at sea level and at the rated altitude,

(ii) The maximum continuous rated manifold pressure, in the case of engines the maximum continuous power of which is governed by a constant manifold pres

sure.

(h) Propellers and rotors (1) Rotor. Rotor is a system of rotating airfoils. (2) Main rotor. The main rotor is the main system of rotating airfoils providing sustentation for the rotorcraft.

(3) Auxiliary rotor. An auxiliary rotor is one which serves either to counteract the effect of the main rotor torque on the rotorcraft, or to maneuver the rotorcraft about one or more of its three principal axes.

(4) Axis of no feathering. The axis of no feathering is the axis about which there is no first harmonic feathering or cyclic pitch variation."

(5) Plane of rotor disc. The plane of rotor disc is a reference plane at right angles to the axis of no feathering.

(6) Tip speed ratio. The tip speed ratio is the ratio of the rotorplane flight velocity component in the plane of rotor disc to the rotational tip speed of the rotor blades expressed as follows:

(i) Fire protection · (1) Fireproof. Fireproof material means a material which will withstand heat at least as well as steel in dimensions appropriate for the purpose for which it is to be used. When applied to material and parts used to confine fires in designated fire zones, fireproof means that the material or part will perform this function under the most severe conditions of fire and duration likely to occur in such zones.

(2) Fire-resistant. When applied to sheet or structural members, fire-resistant material means a material which

For propeller airworthiness requirements see Part 14 of this subchapter.

a See NACA Technical Note No. 1604.

will withstand heat at least as well as aluminum alloy in dimensions appropriate for the purpose for which it is to be used. When applied to fluid-carrying lines, other flammable fluid system components, wiring, air ducts, fittings, and powerplant controls, this term refers to a line and fitting assembly, component, wiring or duct, or controls which will perform the intended functions under the heat and other conditions likely to occur at the particular location.

(3) Flame-resistant. Flame-resistant material means material which will not support combustion to the point of propagating, beyond safe limits, a flame after the removal of the ignition source.

(4) Flash-resistant. Flash-resistant material means material which will not burn violently when ignited.

(5) Flammable. Flammable pertains to those fluids or gases which will ignite readily or explode.

[21 F.R. 10291, Dec. 22, 1956, as amended by Amdt. 6-3, 23 F.R. 2592, Apr. 19, 1958; 24 F.R. 5, Jan. 1, 1959; Amdt. 6-4, 24 F.R. 7073. Sept. 1, 1959]

The provisions of this section shall apply to all rotorcraft types certificated under this part irrespective of the date of application for type certificate.

(a) Unless otherwise established by the Administrator, the rotorcraft shall comply with the provisions of this part together with all amendments thereto effective on the date of application for type certificate, except that compliance with later effective amendments may be elected or required pursuant to paragraphs (c), (d), and (e) of this section.

(b) If the interval between the date of application for type certificate and the issuance of the corresponding type certificate exceeds three years, a new appli

cation for type certificate shall be required, except that for applications pending on May 1, 1954, such three-year period shall commence on that date. At the option of the applicant, a new application may be filed prior to the expiration of the three-year period. In either instance the applicable regulations shall be those effective on the date of the new application in accordance with paragraph (a) of this section.

(c) During the interval between filing the application and the issuance of a type certificate, the applicant may elect to show compliance with any amendment of this part which becomes effective during that interval, in which case all other amendments found by the Administrator to be directly related shall be complied with.

(d) Except as otherwise provided by the Administrator pursuant to § 1.24 of this subchapter, a change to the type certificate (see § 6.13(b)) may be accomplished, at the option of the holder of the type certificate, either in accordance with the regulations incorporated by reference in the type certificate pursuant to § 6.13(c), or in accordance with subsequent amendments to such regulations in effect on the date of application for approval of the change, subject to the following provisions:

(1) When the applicant elects to show compliance with an amendment to the regulations in effect on the date of application for approval of a change, he shall show compliance with all amendments which the Administrator finds are directly related to the particular amendment selected by the applicant.

(2) When the change consists of a new design or a substantially complete redesign of a component, equipment installation, or system installation of the rotorcraft, and the Administrator finds that the regulations incorporated by reference in the type certificate pursuant to § 6.13 (c) do not provide complete standards with respect to such change, he shall require compliance with such provisions of the regulations in effect on the date of application for approval of the change as he finds will provide a level of safety equal to that established by the regulations incorporated by reference at the time of issuance of the type certificate.

NOTE: Examples of new or redesigned components and installations which might re

quire compliance with regulations in effect on the date of application for approval, are: New powerplant installation which is likely to introduce additional fire or operational hazards unless additional protective measures are incorporated; the installation of a new rotor system or a new electric power system.

(e) If changes listed in subparagraphs (1) through (3) of this paragraph are made, the rotorcraft shall be considered as a new type, in which case a new application for type certificate shall be required and the regulations together with all amendments thereto effective on the date of the new application shall be made applicable in accordance with paragraphs (a), (b), (c), and (d) of this section.

(1) A change in the number of engines or rotors;

(2) A change to engines or rotors employing different principles of operation or propulsion;

(3) A change in design, configuration, power, or weight which the Administrator finds is so extensive as to require a substantially complete investigation of compliance with the regulations.

[21 F.R. 10291, Dec. 22, 1956, as amended, 24 F.R. 5, Jan. 1, 1959]

(a) The applicant for a type certificate shall submit to the Administrator such descriptive data, test reports, and computations as are necessary to demonstrate that the rotorcraft complies with the requirements of this part.

(b) The descriptive data required in paragraph (a) of this section shall be known as the type design and shall consist of such drawings and specifications as are necessary to disclose the configuration of the rotorcraft and all the design features covered in the requirements of this part, such information on dimensions, materials, and processes as is necessary to define the structural strength of the rotorcraft, and such other data as are necessary to permit by comparison the determination of the airworthiness of subsequent rotorcraft of the same type.

After proof of compliance with the structural requirements contained in this part, and upon completion of all necessary inspections and testing on the ground, and proof of the conformity of the rotorcraft with the type design, and upon receipt from the applicant of a report of flight tests performed by him, the following shall be conducted:

(a) Such official flight tests as the Administrator finds necessary to determine compliance with the requirements of this part.

(b) After the conclusion of flight tests specified in paragraph (a) of this sec

tion, such additional flight tests as the Administrator finds necessary to ascertain whether there is reasonable assurance that the rotorcraft, its components, and equipment are reliable and function properly. The extent of such additional flight tests shall depend upon the complexity of the rotorcraft, the number and nature of new design features, and the record of previous tests and experience for the particular rotorcraft type, its components, and equipment. If prac

ticable, these flight tests shall be conducted on the same rotorcraft used in the flight tests specified in paragraph (a) of this section and in the rotor drive endurance tests specified in § 6.412.

§ 6.17 Airworthiness, experimental, and

production certificates.

(For requirements with regard to these certificates see Part 1 of this subchapter.)

§ 6.18 Approval of materials, parts, processes, and appliances.

(a) Materials, parts, processes, and appliances shall be approved upon a basis and in a manner found necessary by the Administrator to implement the pertinent provisions of the regulations in this subchapter. The Administrator may adopt and publish such specifications as he finds necessary to administer this regulation, and shall incorporate therein such portions of the aviation industry, Federal and military specifications respecting such materials, parts processes, and appliances as he finds appropriate.

NOTE: The provisions of this paragraph are intended to allow approval of materials. parts, processes, and appliances under the system of Technical Standard Orders, or in conjunction with type certification procedures for a rotorcraft, or by any other form of approval by the Administrator.

(b) Any material, part, process, or appliance shall be deemed to have met the requirements for approval when it meets the pertinent specifications adopted by the Administrator, and the manufacturer so certifies in a manner prescribed by the Administrator.

§ 6.18-1' Approval of aircraft components (FAA rules which apply to § 6.18).

Aircraft components made the subject of technical standards orders shall be

'Appears at 16 F. R. 672 as § 6.6-1.