components shall be provided for each heater to automatically shut off and hold off the ignition and fuel supply to the heater at a point remote from the heater when the heat exchanger temperature or ventilating air temperature exceeds safe limits or when either the combustion airflow or the ventilating airflow becomes inadequate for safe operation. [21 F.R. 3999, May 22, 1956, as amended by Amdt. 3-2, 22 F.R. 5561, July 16, 1957] § 3.388-1 Heater isolation (FAA policies which apply to § 3.388 (b)).

(a) Under §§ 3.388(b) and 3.623, heaters should be isolated from the remainder of the airplane by means of a fire

proof shield. However, this need not necessarily mean a complete shield around the entire heater unit (although this would be satisfactory) since in many heater designs, a fireproof air jacket largely surrounds the flame chamber. Thus, the heater design itself practically provides a steel shield between the combustion unit and the remainder of the airplane. In such cases, it should suffice to provide isolation for the fuel system components mounted on the heater and for the heater exhaust and combustion chamber drains.

(b) The following schematic sketch shows an example of an installation which should be satisfactory:

SHUT-OFF VALVE

The shut-off valve shown in the sketch should be provided if there are fuel system components within the ventilating air shroud which may be subject to leakage or failure. In such cases, that portion of the ventilating air duct up to the valve, as well as the valve itself, should be of fire resistant construction and the valve should provide as flame tight a seal as possible. If the fuel system is so arranged that there are no fittings or connections within the ventilating air shroud, the downstream air shut-off valve and fire resistant duct between the heater and the valve may be dispensed with.

(c) As regards shrouds for the combustion chamber drain lines, the necessity for these will generally depend upon the location of the drain in the heater. If the drain outlet from the combustion chamber is so located that products of combustion can issue through the drain line, it will no doubt become hot and require isolation. However, drains are

sometimes connected in such a manner that they do not carry exhaust gases and remain relatively cool. In such cases, shrouds are not necessary.

[Supp. 10, 16 F. R. 3290, Apr. 14, 1951]

§ 3.388-2 Fire-detector and extinguisher equipment (FAA policies which apply to § 3.388 (b)).

(a) For nontransport category airplanes equipment of this type is not required. If such equipment is installed and it is shown to provide equivalent safety to the use of fireproof isolation, it may be considered a suitable alternative for fireproof isolation provisions discussed in § 3.388-1(b). In such cases, the detection and extinguishing provisions should comply with the requirements for transport category airplanes; that is, detectors and extinguishers should be provided wherever potential sources of fuel leakage and sources of ignition are in close proximity.

(b) In the sketch in § 3.388-1 (b) the space within the shield would require such protection. In addition, detectors - and extinguisher nozzles should be installed in the ventilating air passages of the heater if this chamber contains fuel system fittings or connections that may be subject to leakage.

(c) Hand fire extinguishers should be - considered equivalent to a fixed fire extinguisher installation only when the heater is located in such a manner that it is readily accessible to the crew and when all fire zones in the installation can easily be reached with a hand extinguisher.

(d) All extinguishers may also be dispensed with when the heater is so shielded and located that a fire could be permitted to burn itself out without danger of damage to any important structural members or otherwise endangering the safety of the airplane.

(e) Detectors may be dispensed with as an alternative to fireproof isolation, only when the heater is so located that the occurrence of fire would immediately be noted by the crew.

[Supp. 10, 16 F. R. 3290, Apr. 14, 1951] § 3.388-3 Heater fuel system

(FAA policies which apply to § 3.388(b). (a) The heater fuel system should comply with airworthiness standards for the engine fuel system as regards fuel lines, fittings and accessories.

(b) Valves should be provided for shutting off in flight the flow of fuel at its source, unless equivalent provisions in the form of a separate heater fuel pump are available.

(c) All pressure lines should comply with the provisions of § 3.432 regarding pressure cross feed arrangements. [Supp. 10, 16 F. R. 3291, Apr. 14, 1951] § 3.388-4 Combustion heaters (FAA rules which apply to § 3.388(b)). The minimum safety requirements for combustion heaters which are intended for use in civil aircraft have been established by the Administrator in Technical Standard Order No. TSO-C20, effective June 15, 1949, "Combustion Heaters" (§ 514.20 of this title).

[Supp. 10, 16 F. R. 3291, Apr. 14, 1951]

✰ PERSONNEL AND CARGO ACCOMMODATIONS

§ 3.389 Doors.

Closed cabins on all airplanes carrying passengers shall be provided with at

least one adequate and easily accessible external door. No passenger door shall be so located with respect to the propeller discs as to endanger persons using the door.

§ 3.390 Seats and berths.

All seats and berths shall be of an approved type. They and their supporting structures shall be designed for an occupant weighing at least 170 pounds (190 pounds with parachute for seats intended for the acrobatic and utility categories) and for the maximum load factors corresponding with all specified flight and ground load conditions including the emergency landing conditions prescribed in § 3.386. The provisions of paragraphs (a) through (d) of this section shall also apply:

(a) Pilot seats shall be designed for the reactions resulting from the application of pilot forces to the primary flight controls as prescribed in § 3.231.

(b) All seats in the U and A categories shall be designed to accommodate passengers wearing parachutes, unless placarded in accordance with § 3.74 (b).

(c) Berths shall be so designed that the forward portion is provided with a padded end board, a canvas diaphragm, or other equivalent means, capable of withstanding the static load reaction of the occupant when subjected to the forward accelerations prescribed in § 3.386. Berths shall be provided with an approved safety belt and shall be free from corners or protuberances likely to cause serious injury to a person occupying the berth during emergency conditions. Berth safety belt attachments shall withstand the critical loads resulting from all relevant flight and ground load conditions and from the emergency landing conditions of § 3.386 with the exception of the forward load.

(d) In determining the strength of the attachment of the seat and berth to the structure, the accelerations prescribed in § 3.386 shall be multiplied by a factor of 1.33.

§ 3.390-1 Approved seats and berths (FAA interpretations which apply to § 3.390).

An approved seat or berth is one which complies with the pertinent requirements in the regulations in this subchapter as implemented by TSO-C25 "Aircraft Seats and Berths" (§ 514.25 of this title).

[Supp. 14, 17 F. R. 9066, Oct. 11, 1952]

§ 3.390-2 Proof of strength for seats and berths and their installations (FAA policies which apply to § 3.390).

(a) Proof of compliance with strength and deformation requirements for seats and berths, approved as a part of the type design, and for all seat and berth installations, may be shown by one of the following methods:

(1) Structural analysis alone when the structure conforms with conventional types for which existing methods of analysis are known to be reliable.

(2) A combination of structural analysis and static load tests to limit loads. (3) Static load tests alone when such tests are carried to ultimate loads. [Supp. 14, 17 F. R. 9066, Oct. 11, 1952] § 3.390-3 Application of loads (FAA policies which apply to § 3.390).

The actual forces acting on seats, berths, and supporting structure in the various flight, ground and emergency landing conditions will consist of many possible combinations of forward, sideward, downward, upward, and aft loads. However, in order to simplify the structural analysis and testing of these structures, it will be permissible to assume that the critical load in each of these directions, as determined from the prescribed flight, ground, and emergency landing conditions, acts separately. If the applicant desires, selected combinations of loads may be used, provided the required strength in all specified directions is substantiated (TSO C-25, Aircraft Seats and Berths, § 514.25 of this title, outlines acceptable methods for testing seats and berths).

[Supp. 17, 18 F. R. 5563, Sept. 17, 1953]

§ 3.392 Cargo compartments.

Each cargo compartment shall be designed for the placarded maximum weight of contents and critical load distributions at the appropriate maximum load factors corresponding to all specified flight and ground load conditions. Suitable provisions shalle be made to prevent the contents of cargo compartments from becoming a hazard by shifting. Such provisions shall be adequate to protect the passengers from injury by the contents of any cargo compartment when the ultimate forward acting accelerating force is 4.5g.

§ 3.392-1

Load factors for design of cargo compartments located in the fuselage (FAA interpretations which apply to § 3.392).

(a) It would seem on examination of §§ 3.392 and 3.386 that there is a conflict between the load factors required for the design of cargo compartments which are located in the fuselage. The following explanation should clarify this possible misconception:

(1) Section 3.392 was specially promulgated to overcome objections to the excessively heavy cargo compartment structure that would be required to meet the crash conditions of § 3.386. In past cases of crashes, injuries to passengers caused by shifting cargo or baggage have not been prevalent despite the fact that in many cases the lower design factors of Bulletin 7a and Part 4a of this subchapter were in effect. Because of this. § 3.392 was incorporated in the requirements, to apply specifically to cargo compartments. It should therefore not be necessary to consider the strength requirements of § 3.386 in their design. [Supp. 10, 16 F. R. 3291, Apr. 14, 1951] § 3.393

Ventilation.

All passenger and crew compartments shall be suitably ventilated. Carbon monoxide concentration shall not exceed 1 part in 20,000 parts of air.

§ 3.394 Pressurized cabins ; general.

The design of pressurized cabins shall comply with the requirements of §§ 3.395 and 3.396. (See also §§ 3.197, 3.270, and 3.383.)

[Amdt. 3-2, 22 F. R. 5561, July 16, 1957]

§ 3.395 Pressure control.

Pressurized cabins shall be provided with at least the following valves, controls, and indicators for controlling cabin pressure:

(a) Two pressure relief valves, at least one of which is the normal regulating valve, shall be installed to limit automatically the positive pressure differential to a predetermined value at the maximum rate of flow delivered by the pressure source. The combined capacity of the relief valves shall be such that the failure of any one valve would not cause an appreciable rise in the pressure differential. The pressure differential shall be considered positive when the internal pressure is greater than the external.

3

(b) To reverse pressure differential e relief valves (or equivalent) shall be d installed to prevent automatically a at negative pressure differential which

would damage the structure, except that one such valve shall be considered sufficient if it is of a design which reasonably precludes its malfunctioning.

(c) Means shall be provided by which the pressure differential can be rapidly equalized.

(d) An automatic or manual regulator for controlling the intake and/or exhaust air flow shall be installed so that the required internal pressures and air flow rates can be maintained.

(e) Instruments shall be provided for the pilot to show the pressure differential, the absolute pressure in the cabin, and the rate of change of the absolute pressure.

(f) Warning indication shall be provided for the pilot to indicate when the safe or preset limits on pressure differential and on absolute cabin pressure are exceeded.

(g) If the structure is not designed for pressure differentials up to the maximum relief valve setting in combination with landing loads (see §3.197 (b)), a warning placard shall be provided for the pilot.

(h) If continued rotation of an engine-driven cabin compressor or if continued flow of any compressor bleed air will constitute a hazard in case malfunction occurs, means shall be provided to stop rotation of the compressor or to divert air flow from the cabin. [Amdt. 3-2, 22 F. R. 5561, July 16, 1957] § 3.396 Tests.

(a) Strength test. The complete pressurized cabin, including doors, windows, canopy, and all valves shall be tested $ as a pressure vessel for the pressure differential specified in § 3.197(c).

(b) Functional tests. The following functional tests shall be performed:

(1) To simulate the condition of regulator valves closed, the functioning and the capacity shall be tested of the positive and negative pressure differential valves and of the emergency release valve.

(2) All parts of the pressurization system shall be tested to show proper functioning under all possible conditions of

pressure, temperature, and moisture up to the maximum altitude selected for certification.

(3) Flight tests shall be conducted to demonstrate the performance of the pressure supply, pressure and flow regulators, indicators, and warning signals in steady and stepped climbs and descents at rates corresponding with the maximum attainable without exceeding the operating limitations of the airplane up to the maximum altitude selected for certification.

(4) All doors and emergency exits shall be tested to ascertain that they operate properly after being subjected to the flight tests prescribed in subparagraph (3) of this paragraph.

[Amdt. 3-2, 22 F. R. 5562, July 16, 1957] MISCELLANEOUS

§ 3.401 Leveling marks.

Leveling marks shall be provided for leveling the airplane on the ground. Subpart E-Powerplant Installations; Reciprocating Engines

GENERAL

§ 3.411 Components.

(a) The powerplant installation shall be considered to include all components of the airplane which are necessary for its propulsion. It shall also be considered to include all components which affect the control of the major propulsive units or which affect their continued safety of operation.

(b) All components of the power-plant installation shall be constructed, arranged, and installed in a manner which will assure the continued safe operation of the airplane and power plant. Accessibility shall be provided to permit such inspection and maintenance as is necessary to assure continued airworthiness. § 3.411-1 Powerplant installation components (FAA interpretations which apply to § 3.411).

The term "all components" includes engines and propellers and their parts, appurtenances, and accessories which are furnished by the engine or propeller manufacturer and all other components of the powerplant installation which are furnished by the airplane manufacturer. For example: Fuel pumps, lines, valves,

and other components of the fuel system which are integral parts of the type certificated engine are also components of the airplane powerplant installation. [Supp. 33, 23 F. R. 9018, Nov. 20, 1958]

ENGINES AND PROPELLERS

§3.415 Engines.

Engines installed in certificated airplanes shall be of a type which has been certificated in accordance with the provisions of Part 13 of this subchapter.

§ 3.416 Propellers.

(a) Propellers installed in certificated airplanes shall be of a type which has been certificated in accordance with the provisions of Part 14 of this subchapter.

(b) The maximum engine power and propeller shaft rotational speed permissible for use in the particular airplane involved shall not exceed the corresponding limits for which the propeller has been certificated.

(c) When propeller control design permits stopping of crankshaft rotation of any engine in flight by feathering the propeller, means shall be provided for unfeathering each propeller individually in flight.

[21 F.R. 3339, May 22, 1956, as amended by Amdt. 3-5, 24 F.R. 7066, Sept. 1, 1959]

§ 3.417 Propeller vibration.

In the case of propellers with metal blades or other highly stressed metal components, the magnitude of the critical vibration stresses under all normal conditions of operation shall be determined by actual measurements or by comparison with similar installations for which such measurements have been made. The vibration stresses thus determined shall not exceed values which have been demonstrated to be safe for continuous operation. Vibration tests may be waived and the propeller installation accepted on the basis of service experience, engine or ground tests which show adequate margins of safety, or other considerations which satisfactorily substantiate its safety in this respect. In addition to metal propellers, the Administrator may require that similar substantiation of the vibration characteristics be accomplished for other types of propellers, with the exception of conventional fixed-pitch wood propellers.

§ 3.418 Propeller pitch and speed limitations.

The propeller pitch and speed shall be limited to values which will assure safe operation under all normal conditions of operation and will assure compliance with the performance requirements specified in §§ 3.81-3.86.

§ 3.419 Speed limitations for fixed-pitch propellers, ground adjustable pitch propellers, and automatically vary. ing pitch propellers which cannot be controlled in flight.

(a) During take-off and initial climb at best rate-of-climb speed, the propeller, in the case of fixed-pitch or ground adjustable types, shall restrain the engine to a speed not exceeding its maximum permissible take-off speed and, in the case of automatic variable-pitch types, shall limit the maximum governed engine revolutions per minute to a speed not exceeding the maximum permissible take-off speed. In demonstrating compliance with this provision the engine shall be operated at full throttle or the throttle setting corresponding to the maximum permissible take-off manifold pressure.

(b) During a closed throttle glide at the placard, "never-exceed speed" (see § 3.739), the propeller shall not cause the engine to rotate at a speed in excess of 110 percent of its maximum allowable continuous speed.

§ 3.419-1 Propeller pitch and speed lim. itations (FAA interpretations which apply to § 3.419).

(a) The low pitch setting should comply with § 3.419 (a) which states that the propeller shall not exceed the rated engine take-off r.p.m. with take-off power (full throttle unless limited by manifold pressure) during take-off and initial climb at best rate of climb speed. It is not permissible to use a lower pitch setting than that specified above in order to obtain take-off r.p.m. at the best angle of climb speed for the purpose of showing compliance with § 3.85 (c), Balked Landing Conditions. An exception to the above may be granted in the specific case covered by § 3.85-5, when satisfactory engine cooling can be demonstrated at the best angle of climb speed in the balked landing configuration (§ 3.85 (c)). However, in cases where the interpretation of § 3.85 does not govern, it will be necessary to con