§ 18.30-19 Progressive inspection (FAA rules which apply to § 18.30(c)).

(a) General. The progressive inspection is designed to permit the increased utilization of an aircraft, particularly a multiengine type, by scheduling inspections through the use of a planned inspection schedule.

(b) Routine and detailed inspections. The inspection system will consist of a routine inspection which provides a visual examination or check of the aircraft and its components and systems insofar as practicable without disassembly, and a detailed inspection which will permit a thorough examination of the aircraft and its components and systems by such disassembly as necessary. Since the overhaul of a component or system includes a thorough examination, such overhaul will be considered to be a detailed inspection. The frequency and detail of both the routine and detailed inspections shall provide complete inspection of the aircraft within each 12 calendar months and be consistent with the manufacturer's recommendations, field service experience, and the type of operation in which the aircraft is engaged to insure that the aircraft and its components and systems are in an airworthy condition and conform with the applicable FAA aircraft specifications and airworthiness directives, or other approved data. Such inspections shall include, but not be limited to, the items specified in appendix D.'

(c) Inspection schedule. The frequency of both inspections shall be outlined in the form and manner specified in the example of progressive inspection schedule contained in appendix D2 and shall specify the intervals when the inspection or overhauls will be performed, either in hours or days, as appropriate.

(d) Inspection procedures. A progressive inspection shall be conducted in accordance with the following procedures:

(1) The aircraft shall be inspected completely at the commencement of a progressive inspection. Thereafter, routine and detailed inspections shall be conducted at regular intervals in accordance with the inspection schedule. Normally, all inspection shall be conducted by the inspecting agency having

' Appendix D not filed with the Office of the Federal Register.

responsibility for the progressive inspec-830 tion of such aircraft. However, where an aircraft is en route when inspections become due, routine and detailed inspec- P tions may be performed by an appropriately rated and certificated mechanic. or repair station, or the manufacturer provided such inspections are conducted in accordance with the forms and pro-Ja cedures to be furnished by the inspecting facility which would otherwise conduct the inspection of the aircraft. Upon completion of the inspection, such inspection forms shall be returned to the inspecting agency furnishing the forms for their records. When an aircraft is y no longer to be inspected in accordance res with a progressive inspection, the first periodic will be due within 12 calendar months after the last complete inspection of the aircraft under the progres-c sive. If passengers are carried for hire the 100-hour inspection will be due within 100 hours after such last complete inspection. A complete inspection of the aircraft, for the purpose of determining when the periodic and 100-hour inspections are due, will require a de- 1 tailed inspection of the aircraft and all its components in accordance with the progressive inspection. For example, a routine inspection of the aircraft and a detailed inspection of several components will not be considered to be a complete inspection.

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(e) Records. Upon the satisfactory completion of a routine or detailed in-e spection conducted in accordance with a progressive inspection system, the me- s chanic, repair station, or manufacturer d conducting such inspection shall enter a brief description of the extent of the inspection accomplished and the following statement in the aircraft maintenance records, over the mechanic's signature and certificate number, the repair station's or manufacturer's name, signature of authorized personnel, cer-i tificate number, and include aircraft time in service, and date of inspection: A routine inspection of

aircraft or components) spection

(Identify whether and a detailed inwere per

(Identify components) formed in accordance with a progressive inspection and the aircraft is released to service.

[21 F. R. 3182, May 15, 1956]

§ 18.30-20 Procedures covering major alteration of approved radio equipment (FAA interpretations which apply to § 18.30(b)).

(a) Radio equipment approved under Part 16 of this subchapter. (1) When any major alteration is accomplished on radio equipment type certificated prior to January 1, 1953, such equipment shall comply with the requirements of Part 16 of this subchapter which were effective on the date of its type certification, provided the environmental test procedures contained in RTCA Paper 100-54/DO-60 may be used in lieu of the test procedures prescribed under Part 16 of this subchapter.

(2) When any major alteration is accomplished on radio equipment type certificated on or after January 1, 1953, such equipment shall comply with the requirements of Part 16 of this subchapter and RTCA Paper 100-54/DO-60,' which are the environmental test requirements specified in § 16.30-3 of this subchapter. [Supp. 5, 20 F. R. 7535, Oct. 8, 1955] § 18.30-21 Testing approved radio equipment after alteration (FAA policies which apply to § 18.30(b)). Where an FAA representative approval of major alteration to approved radio equipment is required, it will be necessary that such equipment, prior to such approval and at the discretion of the FAA representative, be subjected to any or all tests prescribed in Part 16 of this subchapter or the pertinent Technical Standard Order as applicable in order to determine whether the equipment meets the prescribed airworthiness requirements.

[Supp. 5, 20 F. R. 7535, Oct. 8, 1955]

§ 18.30-22 Radio systems (FAA policies which apply to § 18.30).

Aircraft radio systems should be maintained, repaired, altered, and installed in accordance with the equipment manufacturer's maintenance instructions or manuals and the following standards.

1RTCA Paper 100-54/DC-60 was made effective as part of radio equipment type certification requirements by § 16.30-3 of this subchapter, as amended on April 15, 1955. The amendment made no changes in the requirements contained in RTCA Paper 5052/DO-44 which was referred to in § 16.30-3 of this subchapter, effective January 1, 1953.

(a) Wiring. Radio systems should be wired to minimize the possibility of fire or smoke hazards or unsatisfactory operation of the radio equipment.

(1) The radio systems should be connected to the airplane electrical system at a terminal strip or by a plug and receptacle connection. Protective devices (fuses or circuit breakers) should be installed in the load circuit. These should, in general, be selected on the basis of the highest rating that will adequately protect the cable. All loads should be connected in such a manner that the master switch of the aircraft will interrupt the circuit when the master switch is opened.

(i) If a terminal strip is used, it should be designed or mounted so that loose metallic objects cannot fall across the terminal posts. Posts should be No. 6 or larger to permit proper tightening of the nuts, thus providing maximum current carrying capacity without a danger of shearing the studs.

(ii) If a plug and receptacle type of connection is used, the soldered connections of the wire to the plug and receptacle inserts should be individually insulated from each other and from other metallic parts of the plug and receptacle.

(2) Junction boxes should be used for enclosure of terminal strips. The boxes should be made from a fire-resistant, nonabsorbent material, such as aluminum alloy, or an acceptable plastic material. They should be of sufficiently rigid construction to prevent "oilcanning" of the box sides, thus avoiding the possibility of the sides causing internal shorts. They should be designed and installed to permit easy access to the enclosed terminals and to allow any loose metallic parts to fall away from the terminals. Sufficient space should be provided in the junction box so that it will not be necessary to bend the wires sharply as they leave the terminal strip. The terminal strip should be mounted within the box rather than on the inside of the box cover.

(3) Interconnecting wires and cables between various pieces of radio equipment should be supported by insulated clamps so that they do not rub against the airplane or each other under vibration conditions encountered in flight.

(b) Location of radio equipment. The equipment, controls, and indicators should be located where they can be

satisfactorily operated and read respectively from the appropriate crew member station. The equipment should be so located that there is sufficient air circulation to avoid overheating of the equipment. Also, clearance should be provided between high temperature areas of the equipment and readily flammable parts of the airplane.

(c) Mounting of radio equipment. The equipment should be attached to the airplane by means of locking devices to prevent loosening in service from vibration. Examples are self-locking nuts, serrated washers, cotter pins, self-locking hold down clamps, or snap-slides and hold down assembly nuts which are safety wired. Mechanical remote control devices should have the control cable so routed and so supported as to prevent kinking, binding or abrasion. Items mounted on shock mounts should have sufficient clearance for normal vibration and swaying of the equipment without hitting adjacent equipment or parts of the airplane. Electrical and mechanical cables to shock mounted equipment should be routed and supported so that they will not be unduly stressed by motion of the equipment. In order that the occupants will not be endangered by moving equipment during minor crash landings, the equipment mounting and rack should be capable of withstanding ultimate accelerations for which the airplane was designed.

(d) Bonding. Radio equipment should be bonded to the airplane in order to provide a low resistance ground circuit and to minimize radio interference from static electrical charges. Nonconducting finishes, such as paint and anodizing films should be carefully removed from the attachment surface under the bonding terminal. Bonding jumpers should be as short as practicable and be installed in such manner that the resistance of each connection does not exceed 0.003 ohm. Where a jumper is for radionoise prevention only and not for current carrying purposes, a resistance of 0.01 ohm is satisfactory. Aluminum alloy or tinned or cadmium plated copper jumpers' should be used for bonding alumi

When aluminum or its alloys are in contact with most metals (exceptions are magnesium and zinc), current will flow from the aluminum to the other metals. The result will be that the aluminum will corrode. In order to minimize such corrosion, metals other than magnesium and zinc when in con

num alloy parts and copper, brass or bronze jumpers should be used to bond steel parts.

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(e) Available power supply. clude overloading the electric power system of the airplane when additional equipment is added, an electrical load analysis should be made to determine whether the available power is adequate. Radio equipment should operate satisfactorily throughout the voltage range of the aircraft electrical system under taxi, takeoff, slow cruise, normal cruise, b and landing operating conditions. If night and instrument flight is contem- * plated, the electrical load analysis it should be computed for the above flight regimes under the most adverse tempera-ak ture conditions with night and instru- ( ment flight.

(f) Elimination of engine ignition r noise. (1) The most effective method of minimizing engine ignition interference is to shield the ignition system. This involves enclosing in metal all parts of the circuits which might radiate noise. Ignition wires having a metallic-braid covering and special end connectors should be used between the magneto and spark plugs. The primary leads to the magneto and the magneto switch itself should be shielded. Shielded type spark plugs and a shielded metal cover for the magneto, if it is not of a shielded type, should be provided. All connections in the shielding system should be tight metal to metal contact.

(2) If it is not feasible to shield the engine ignition system, the engine ignition noise may be suppressed by replacing the spark plugs with resistor spark plugs of a type approved for the engine.

(3) If it is found that despite shielding of the ignition wiring and plugs an intolerable noise level is present in the radio system, it may be necessary to provide a filter between the magneto and magneto switch to attenuate the noise. This may consist of a single bypass capacitor or a combination of capacitors and choke coils. When this is done, the shielding between the filter and magneto switch can usually be eliminated and the special shielded magneto switch need not be used.

tact with aluminum should be cadmium plated. Where contact between dissimilar metals cannot be avoided, care should be taken to minimize corrosion by putting a protective coating on the finished connection.

Supporting brackets and wiring details for magneto filters should be in conformance with standard aircraft electrical practice. The reliability of the magneto filter installation should be at least equivalent to that of the remainder of the magneto ground lead installation.

(g) Antennas, general. It is satisfactory to use one antenna for transmission and reception of communications provided such antenna is a satisfactory compromise for the frequencies to be used. In a single antenna installation of this type, the antenna should I be connected to the receiver and be switched automatically to the transmitter when the microphone "push-totalk" switch is actuated.

(1) Fixed and trailing wire antenna installations should be tailored to fit the particular type of aircraft. Other types of antennas are much more compact and may be installed as complete units on various types of aircraft.

(2) Masts used to support a fixed-wire : antenna should be as long as practicable to separate the antenna from the fuselage and/or wings in order to provide an effective antenna. Masts should be firmly attached to the airplane structure. If an antenna is attached at the trailing edge of wings and leading edge of hori:zontal stabilizers, the attachment should be made to lugs firmly fixed to the structure. The lugs should be welded, riveted, clamped, or bolted, whichever method is most suitable to the structure.

(h) Range receiver antennas (200 to 400 kc). A "T", "L", or "V" type antenna should be used and mounted on the top or bottom of the airplane (see Figure 1) with an approximate clearance of one foot from the fuselage and wings.

'Since all radio communication and navigation equipment necessitates the use of antennas for transmission or reception of radio frequency energy, care should be exerIcised in the design and installation of antennas and their coupling to the radio equipment. Consideration should be given to the fact that a transmitting antenna is a tuned circuit and that its ability to radiate radio frequency energy into space is governed primarily by the relationship between its length and the frequency of the power to be radiated. In general, the higher the frequency to be transmitted, the shorter the antenna necessary. Receiver antenna design and installation is controlled primarily by the degree of directivity necessary for the particular communication or navigation equipment.

The main leg of the "T" or "L" and each leg of the "V" antenna should be a minimum of 6 feet long. A whip antenna may also be used for range reception. However, since the signal output fed from such an antenna generally is less than that obtained from the other types of antennas mentioned above, a careful check should be made of the completed installation to insure that satisfactory operation will be obtained.

(i) Direction finding antennas (100 to 1750 kc). Manual or automatic loop type antennas are used with direction finder receivers. The loops are designed for use with a particular receiver. Connecting wires between the loops and receivers are also designed for the specific equipment. Accordingly, only components meeting the specification characteristics of the receiver manufacturer should be used.

(1) Loops enclosed in streamlined housings or exposed loops are satisfactory for external mounting on an airplane. Loops may also be installed internally in the airplane when proper attention is given to avoiding interference from metallic structure and skin of the airplane.

(2) The outstanding characteristic of a loop antenna is its directional sensitivity which makes it useful as an accurate navigational device. Various things can reduce this accuracy and should be avoided. Metallic base paints should not be used on the housing. Location of the loop near an engine which has poor ignition shielding should be avoided since this location makes it difficult to detect the "null." Loops should be mounted as far as practical from antennas and interfering metal structures. The preferred locations are on the fore-and-aft center line of the aircraft either above or below the fuselage. In determining the location, consider the space necessary both inside and outside of the fuselage, structural requirements, length of cables, location of

Excessively long antennas are unsatisfactory because they are more directive in reception than relatively short ones. A trailing wire type of antenna will not prove suitable when used with a range receiver because it is highly directive; may cause a loss of distinct "cone of silence"; and changes in the airplane direction which may occur often in range flying cause the antenna to "whip," resulting in breakage and loss of reception. The whipping action may also cause the course signals to shift continuously.

the radio compass unit, and effect on operation and maintenance of the aircraft. Also choose the mounting location to provide a balanced quadrantal error. Quadrantal error is that installation error caused by the metal in the fuselage, wings, etc., distorting the electromagnetic field of a received signal and resulting in azimuth reading inaccuracies which are greatest between the four cardinal points with respect to the center line of the aircraft. When making an installation on the lower part of the fuselage, do not fasten the loop to a primary structural member since,

in the event of a landing with landing gear retracted, the aircraft may be severely damaged. Mount the loop so that it will be level during normal flight.

(3) Following installation of the loop. it will be necessary to check the direction of the radio bearings every 45 degrees from the fore-and-aft axis of the aircraft (preferably every 15 degrees) in order to determine and compensate for

• Compensation of a loop for such error requires technical knowledge of the equipment and its operational use and should be accomplished by a qualified technician.

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