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3.2.8 Care should be taken to ensure that cables or wires will not interfere with the aircraft’s flight, engine, or propeller controls.
3.2.9 When removing older radios, wiring, or power supplies and installing newer solid-state components, weigh the old equipment and perform a new W&B calculation. This is important since differences in the location and weight of equipment will shift the center of gravity (CG).
3.2.10 Refer to AC 43.13-1, Chapter 10, Weight and Balance, and FAA-H-8083-1, Aircraft Weight and Balance Handbook, for additional information on determining W&B.
3.3 Considerations When Installing Avionics Equipment. When installing radio equipment, use areas or locations designated by the airframe manufacturer and use factory-supplied brackets or racks. Follow the aircraft manufacturer’s installation instructions. When this information is not available, use locations in the aircraft of known load-carrying capabilities. Baggage compartments, cabins, or flight deck floors are good mounting platforms provided the floor attachments meet the strength requirements.
Another method is to fabricate support racks, brackets, or shelves and attach them to the aircraft structure to provide a mounting that will withstand the inertia forces stipulated in Chapter 2, Structural Data.
3.3.1 General Considerations. Ensure the following:
3.3.1.1 There is appropriate air circulation to ensure proper cooling and dissipation of any heat generated or present. Consider the flammability characteristics of all associated elements.
3.3.1.2 There are appropriate clearances to prevent mechanical damage to other parts of the aircraft or from other parts of the aircraft.
3.3.1.3 There is protection provided to the component or article from any fluids or fumes that may be expected and that the component or article will not cause any fluids or fumes to be present that may result in damage to the aircraft or its occupants.
3.3.1.4 That any interference, environmental or operational, to an aircraft or any system of the aircraft is identified and minimized as to not affect airworthiness of the aircraft.
3.3.1.5 That flight characteristics of the aircraft are not altered unless appropriately identified and the changes are within the certified design limits.
3.3.2 Structural Consideration. Consider the following:
3.3.2.1 Structural requirements of a mounting must be considered (see Chapter 2).
3-3 Figure 3-1. Force Diagram Normal-Utility Category
3.3.2.2 A lterations that include making additional cutouts or enlargements of existing panel cutouts must be evaluated to maintain structural integrity. Some aircraft instrument panels are load bearing structures.
3.3.2.3 Loads must be determined to be within the structural design limits of the supports.
3.3.2.4 Instrument panels and other panels throughout the aircraft may be structural or nonstructural in design. Structural loads must be adequately transferred to primary airframe members.
3.3.2.5 Methods and practices described elsewhere in this AC and in AC 43.13-1 may be employed for the fabrication of attachments and structure.
Figure 3-2. Typical Fabricated Panel Mounting
3-4 Figure 3-3. Typical Layouts Typi cal layout of an older aircraft Typi cal layout of a newer aircraft
3.3.2.6 Existing structures may be reinforced or strengthened using methods described in AC 43.13-1.
3.4 Instrument Panel Mounting. This paragraph is supplemented by AC 43.13-1, Chapter 4, Metal Structure, Welding, and Brazing, and is applicable to the installation of radio units in instrument panels.
3.4.1 Stationary Instrument Panels—Nonstructural and Structural. The stationary instrument panel in some aircraft is part of the primary structure. Prior to making any additional cutouts or enlargements of an existing cutout, determine if the panel is part of the primary structure. If the panel is structural, make additional cutouts or the enlargement of existing cutouts in accordance with the aircraft manufacturer’s instructions, or substantiate the structural integrity of the altered panel in a manner acceptable to the Administrator.
Radius all corners and remove all burrs from the cutout and drilled holes.
3.4.2 Added Equipment Stationary Instrument Panel. When radio equipment is to be installed in a stationary panel already supporting instruments, glove compartments, etc., determine the capability of the panel to support the total load.
3.4.3 Case Support. To minimize the load on a stationary instrument panel, whenever practicable, install a support between the rear (or side) surface of the radio case and a nearby structural member of the aircraft (see Figure 3-2, Typical Fabricated Panel Mounting).
3.4.4 Added Equipment—Shock-Mounted Panels. When installing radio equipment designed for use in shock-mounted panels, the total accumulated weight of equipment installed must not exceed the weight carrying capabilities of the shock mounts. Determine whether the structure to which the shock mounts are connected is satisfactory for supporting the added weight.
3.4.5 Existing Factory Fasteners. When possible, use existing plate nuts and machine screws provided by the aircraft manufacturer to attach the radio case or rack. If additional fastening is required, use machine screws and elastic stop nuts (preferably plate nuts).
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3.4.6 Magnetic Direction Indicator. As a function of the radio installation, determine if it is necessary to swing the compass. Install a suitable placard that indicates the compass error with the radio(s) on and off. Maximum acceptable deviation in level flight is 10 degrees on any heading. The following is an example of a typical compass calibration card. Refer to AC 43.13-1, Chapter 12, Aircraft Avionics Systems, on how to swing a compass.
Table 3-1. Typical Compass Calibration Card FOR N 30 60 E 120 150 Radio On Steer 4° 35° 63° 93° 123° 154° Radio Off Steer 358° 27° 58° 88° 118° 148°
FOR S 210 240 W 300 330 Radio On Steer 183° 214° 244° 274° 304° 337° Radio Off Steer 178° 208° 238° 268° 293° 327°
3.5 Other Mounting Areas. The following are acceptable methods for installing radio equipment at other than instrument panel locations.
3.5.1 Shock-Mounted Units.
3.5.1.1 Wood or Composition Flooring. Secure the shock-mounted base assembly (suitable for radio unit) directly to the floor using machine screws. Add a doubler to the bottom of the floor, thereby sandwiching the composition floor between each shock-mount foot and the doubler. Subsequent removal and reinstallation of the shock-mount foot will be facilitated if plate nuts are secured to the doubler. Where practicable, use small retaining screws to keep the doubler in position. Install a ground strap between the radio rack and metal structure of the aircraft.
3-6 Figure 3-4. Typical Shock-Mounted Base (Wood or Composition Flooring)
3.5.1.2 M etal Flooring. Secure the shock-mounted base assembly directly to the floor using machine screws, washers, and self-locking nuts. Floor area under and around the radio mounting bases may require installation of doublers or other reinforcement to prevent flexing and cracking. Installation of plate nuts on the floor or doubler will facilitate removal and installation of the shock mounts. Install a ground strap between the shock mount foot and the radio rack.
Figure 3-5. Typical Shock-Mounted Base (Metal Flooring)
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3.5.2 Rigid-Mounted Unit Base. Secure radio mounting base plate(s) to the floor (wood, composite, or metal) using machine screws as shown in Figure 3-6. Use a reinforcing plate or large area washers or equivalent under wood or composite flooring. When the mounting base is secured to wood or composite material, install a ground strap between the base and aircraft metal structure.
Figure 3-6. Typical Rigid Base Plate Mount
3.6 Fabrication of Supporting Brackets for Attachment to a Structure Other Than Flooring.
3.6.1 Typical supporting brackets usually consist of a shelf or platform upon which the radio unit mounting base assembly can be installed in the same manner as described in paragraph 3.4.
3.6.2 Fabricate the bracket according to good aircraft design, layout, assembly practices, and workmanship to obtain results compatible with the airframe structure. Generally, the thickness of the bracket material will depend on the size or area of the platform and the load it must sustain according to the provisions set forth in Chapter 2.
3.6.3 Use a rivet size and pattern compatible with the aircraft structure to provide the strength needed to ensure support of the loads imposed under all flight and landing conditions.
3-8 Figure 3-7. Typical Underseat Installation No te: To increase the strength of floor attachment points, metal reinforcement may be installed as needed.
3.7 Reinforcement of the Supporting Structure.
3.7.1 Attachments. Attach equipment to the aircraft’s supporting structure so that its supported load will be transmitted to aircraft structural members. If direct attachment to the existing structure (bulkheads, horizontal stringers, etc.) is not feasible, add the necessary stringers, doublers, bulkhead flange reinforcements, etc., to provide adequate support and ensure load transfer to the primary structure. When attaching to the existing structure, ensure the attachment does not weaken the structure. Alteration to the primary structure may require approved engineering data.
3.7.2 Placard. Fasten a permanent placard onto the shelf or bracket (as the example below) stating the design load that the installed structure is determined capable of supporting.
“Shelf load not to exceed __________lbs.”
3-9 Figure 3-8. Typical Remote Unit Mounting Base-Vertical or Horizontal Other Than Structure to Floor
3-10 Figure 3-9. Typical Shelf Installation N ote 1: Use standard aircraft practices and procedures for fabrication and attachment of the shelf. Reinforce fore and aft corners with gussets or a bulb angle.
Note 2: Fabricate a platform using 2017T4(17ST) or equivalent. Apply standard aircraft practices for fabrication and installation.
Note 3: The equipment manufacturer’s mounting bases that meet load requirements and can be utilized are acceptable.
3-11 Figure 3-10. Typical Attachment of Support Structure to Tubular Frame Other Than Structure to Floor
3.8 Electrical Requirements.
3.8.1 Installing an electrical system or component into an aircraft requires consideration of the electrical load, the appropriate power distribution circuit, and available power capacity.
The specific requirements for a system depend on its electrical characteristics and the criticality of its application for use in the aircraft’s operation.
3.8.2 The total energy available to power electrical systems is referred to as the aircraft’s capacity. It includes available stored power and generated power. This will vary depending on the phase of flight or type of operation.
3.8.3 The critical distribution circuit of an aircraft is designed to transfer power from the source to a system determined to be critical to the operation or function of the aircraft. This circuit is required to include additional capacity and circuit protection as required by applicable regulations. Distribution systems should be designed to facilitate loadshedding procedures. Power distribution system design includes the following concerns.
Refer to AC 43.13-1, Chapter 11, Aircraft Electrical Systems, for:
• Circuit protection.
• Wire selection.
• Connectors, switches, and termination devices.
• Wire routing.
• Wiring/cable support.
• Identification.
3.8.4 Installation of Wiring. Select and use wiring of a type and design that is appropriate for the intended purpose of the application. Install in a manner suitably protected from fuel, oil, water, other detrimental substances, oxygen systems, and abrasion damages.
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3.8.5 Power Sources.
3.8.5.1 Connect radio electrical systems to the aircraft electrical system at the power source protective device, a terminal strip, or use a plug and receptacle connection.
3.8.5.2 Radio electrical systems must function properly whether connected in combination or independent.
3.8.6 Protective Devices.
3.8.6.1 Incorporate a “trip free” (one that will trip open if the ON-OFF mechanism is held in the ON position) resettable type circuit breaker or a fuse in the power supply from the bus. Mount in a manner accessible to a crewmember during flight for circuit breaker resetting or fuse replacement and label.
3.8.6.2 Select circuit breakers or fuses that will provide adequate protection against overloading of the radio system wiring.
3.8.6.3 Connect all leads in such a manner that the aircraft’s master switch will interrupt the circuit when the master switch is opened, unless the equipment is intended to be powered when the master switch is open.
3.8.6.4 Radio system controls are to provide independent operation of each system installed and be clearly labeled to identify their function relative to the unit of equipment they operate.
3.8.7 Wire Bundle Separation From Flammable Fluid Lines.
3.8.7.1 Physically separate radio electric wire bundles from lines or equipment containing oil, fuel, hydraulic fluid, alcohol, or oxygen.
3.8.7.2 Mount radio electrical wire bundles above or on level with flammable fluid lines and whenever possible, maintain a minimum separation of 6 inches.
Where separation is 1/2 to 2 inches, install clamps. Refer to AC 43.13-1, Chapter 11, Paragraph 11-127, Flammable Fluids and Gases.
3.8.8 Cable Attachment to Shock-Mounted Units. Route and support electrical wire bundles and mechanical cables in a manner that will allow normal motion of equipment without strain or damage to the wire bundles or mechanical cables.
3.8.9 Radio Bonding. It is advisable to electrically bond radio equipment to the aircraft in order to provide a low impedance ground and to minimize radio interference from static electrical charges. When electrical bonding is used, observe the following:
1. Keep bonding jumpers as short as possible.
2. Prepare bonded surfaces for best contact (resistance of connections should not exceed
0.003 ohm).
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3. Avoid use of solder to attach bonding jumpers. Clamps and screws are preferred.
4. For bonding aluminum alloy, use aluminum alloy or tinned, or cadmium-plated copper jumpers. Use brass or bronze jumpers on steel parts.
5. When contact between dissimilar metals cannot be avoided, put a protective coating over the finished connection to minimize corrosion.
3.9 Electrical Load Analysis Procedure.
3.9.1 Available Power Supply. To preclude overloading the electric power system of the aircraft when additional equipment is added, perform an electrical load analysis to determine whether the available power is adequate. Radio equipment must operate satisfactorily throughout the voltage range of the aircraft electrical system under taxi, takeoff, slow cruise, normal cruise, and landing operating conditions. Compute the electrical load analysis for the most adverse operating conditions; typically, this is for night and/or instrument flight.
3.9.2 ASTM Method. One method for the analysis may be found in the ASTM International F2490-20, Standard Guide for Aircraft Electrical Load and Power Source Capacity Analysis.
3.9.3 Previous Electrical Load Analysis. Applicable elements of a previously performed electrical load analysis if available may be reused.
3.10 Electromagnetic Compatibility (EMC).
3.10.1 EMI may disrupt the performance of systems and has varying degrees of consequence.
These consequences may be identified as no safety effect, minor, major, hazardous, or catastrophic. The purpose of EMC analysis and testing is to ensure that equipment does not cause interference with any existing aircraft system function and that existing systems do not cause any interference with the new equipment (see Table 3-2, Relationship Probabilities and Severity of Failure Conditions).