FIGURE 2-2. TYPICAL FABRICATED PANEL MOUNTING
Machine screws and self-locking nuts Rear case support Rivets or Machine screws and self-locking nuts FIGURE 2-3. TYPICAL LAYOUTS
Typical layout older aircraft
Typical layout newer aircraft
(6) Existing structures may be reinforced or strengthened using methods described in AC 43.13-1 (as amended).
203. INSTRUMENT PANEL MOUNTING. This paragraph is supplemented by AC 43.13-1 (as amended), chapter 2, and is applicable to the installation of radio units in instrument panels.
a. 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 airc raft manufacturers’ 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 “cutout” and drilled holes.
b. 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.
c. 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 (Figure 2-2).
d. Added Equipment—Shock-Mounted Panels. When installing radio equipment designed for use in shock-mounted panels, total accumulated weight of equipment installed must not exceed the weight carrying capabilities of the shock mounts.
Determine that the structure to which the shock mounts are connected is satisfactory for supporting the added weight.
e. Existing Factory Fasteners. When possible, use existing plate nuts and machine screws provided by the aircraft manufacturer for attachment Par 202 Page 11
of the radio case or rack. If additional fastening is required, use machine screws and elastic stop nuts (preferably plate nuts).
f. Magnetic Direction Indicator. As a function of the radio installation, determine if it is necessary to swing the compass. Install a suitable placard which 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 current edition of AC 43.13-1, chapter 12 , on how to swing a compass).
TABLE 2-1. 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°
204. OTHER MOUNTING AREAS. The following are acceptable methods for installing radio equipment at other than instrument panel locations.
a. Shock-mounted Units.
(1) Wood or Composition Flooring.
Secure the shock-mounted base assembly (suitable to 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 doubl er in position. Install a ground strap between the radio rack and metal structure of the aircraft.
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FIGURE 2-4. TYPICAL SHOCK-MOUNTED BASE
Wood Flooring Machine Screw Shock Mount Doubler Plate Nut
(2) Metal Flooring. Secure the shockmounted base assembly directly to the floor using machine screws, washers, and self-locking nuts.
Floor area under and ar ound 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 in stallation of the shock mounts. Install a ground strap between the shock mount foot and the radio rack.
FIGURE 2-5. TYPICAL SHOCK-MOUNTED BASE
Shock Mount Metal Flooring Plate Nut Machine Screw
b. Rigid-Mounted Unit Base. Secure radio mounting base plate(s) to the floor (wood, composite, or metal) us ing machine screws as shown in Figure 2-6. 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.
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FIGURE 2-6. TYPICAL RIGID BASE PLATE MOUNT
Machine Screw Machine Screws and Self-Locking Nuts
205. FABRICATION OF SUPPORTING
BRACKETS FOR ATTACHMENT TO STRUCTURE OTHER THAN FLOORING.
a. 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 applicable paragraph 203.
b. Fabricate bracket in accordance with good aircraft design, layout, assembly practices, and workmanship to obtain results compatible with the airframe structure. Generally, the thickness of bracket material will depend on the size or area of the platform and load it must sustain in accordance with provisions set forth in chapter 1.
c. Use a rivet size and pattern compatible with the aircraft structure to provide the strength needed to assure support of the loads imposed under all flight and landing conditions.
FIGURE 2-7. TYPICAL UNDERSEAT INSTALLATION
Unit attachment ear Plywood floor AN 970 flat washer Machine screw and elastic stop nut 1” clearance with seat occupied and subject to maximum seat spring deflection (6.6 X 170 pounds) downward (load).
Par 205 Page 14
NOTE: To increase the strength of floor attachment points, metal reinforcement may be installed as needed.
206. REINFORCEMENT OF SUPPORTING STRUCTURE.
a. Attach equipment to the supporting structure of the aircraft 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 assure load transfer to the primary structure. When attaching to the existing structure ensure that the attachment does not weaken the structure. Alteration to primary structure may require approved engineering data.
b. Placard. Fasten onto the shelf or bracket a permanent placard (as the example below) stating the design load which the installed structure is determined capable of supporting.
“Shelf load not to exceed __________lbs.”
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FIGURE 2-8. TYPICAL REMOTE UNIT MOUNTING BASE-VERTICAL OR HORIZONTAL
OTHER THAN STRUCTURE TO FLOOR
Par 206 Page 16
Par 206 Page 17 FIGURE 2-9. TYPICAL SHELF INSTALLATION
NOTE: Use standard aircraft practices and procedures for fabrication and attachment of the shelf. Reinforce fore and aft corners with gussets or bulb angle.
NOTE: Fabricate a platform using 2017T4(17ST) or equivalent. Apply standard aircraft practices for fabrication and installation.
NOTE: The equipment manufacturer mounting bases that meet load requirements and can be utilized are acceptable.
FIGURE 2-10. TYPICAL ATTACHMENT OF SUPPORT STRUCTURE TO TUBULAR FRAME
OTHER THAN STRUCTURE TO FLOOR
207. ELECTRICAL REQUIREMENTS.
a. Installation of 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 operation of the aircraft.
b. 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 phase of flight or type of operation.
c. The critical distribution circuit of an aircraft is designed to transfer power from source to a system determined 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 desi gned to facilitate loadshedding procedures. Power distribution system design includes the following concerns. Reference AC 43.13-1 (as amended), chapter 11, for:
(1) Circuit protection.
(2) Wire selection.
(3) Connectors, switches, and termination devices.
(4) Wire routing.
(5) Wiring/cable support.
(6) Identification.
d. Installation of Wiring.
(1) Use a type and design satisfactory for the purpose intended.
(2) Install in a manner suitably protected from fuel, oil, water, other detrimental substances, oxygen systems, and abrasion damages.
e. Power Sources.
(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.
(2) Radio electrical systems must function properly whether connected in combination or independent.
f. Protective Devices.
(1) Incorporate a “trip free” re-settable 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.
(2) Select circuit breakers or fuses that will provide adequate protection against overloading of the radio system wiring.
(3) Connect all leads in such a manner that the master switch of the aircraft will interrupt the circuit when the master switch is opened, unless the equipment is intended to be powered when the master switch is open.
(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.
g. Wire Bundle Separation from Flammable Fluid Lines.
(1) Physically separate radio electric wire bundles from lines or equipment containing oil, fuel, hydraulic fluid, alcohol, or oxygen.
(2) Mount radio electrical wire bundles above flammable fluids lines and securely clamp to the structure. (In no case must radio electrical wire bundles be clamped to lines containing flammable fluids.)
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h. Cable Attachment to Shock-Mounted Units. Route and support electrical wire bundles and mechanical cables in a manner that will allow normal motion of equipmen t without strain or damage to the wire bundles or mechanical cables.
i. 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 surf aces for best contact (resistance of connections should not exceed
0.003 ohm).
(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.
208. ELECTRICAL LOAD ANALYSIS PROCEDURE.
a. 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.
b. One method for the analysis may be found in the ASTM International, Standard Guide for Aircraft Electrical Load and Power Source Capacity Analysis, F 2490-05.
c. Applicable elements of a previously performed electrical load analysis if available may be reused.
209. ELECTROMAGNETIC COMPAT- IBILITY.
a. Electromagnetic Interference (EMI) may disrupt the performance of systems and has varying degrees of consequence. These consequences may be identified as: no safe ty effect, minor, major, hazardous, or catastrophic. The purpose of electromagnetic compatibility (EMC) analysis and testing is to assure 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. (Refer to Table 2-2.)
TABLE 2-2. RELATIONSHIP PROBABILITIES, SEVERITY OF FAILURE CONDITIONS Classification of Failure Conditions No Safety Effect <--Minor--> <--Major--> <--Hazardous--> <--Catastrophic--> Effect on Airplane No effect on operational capabilities or safety Slight reduction in functional capabilities or safety margins Significant reduction in functional capabilities or safety margins Large reduction in functional capabilities or safety margins Normally with hull loss Effect on Occupants Inconvenience for passengers Physical discomfort for passengers Physical distress to passengers, possibly including injuries Serious or fatal injury to an occupant Multiple fatalities Effect on Flightcrew No effect on flightcrew Slight increase in workload or use of emergency procedures Physical discomfort or a significant increase in workload Physical distress or excessive workload impairs ability to perform tasks Fatal Injury or incapacitation
b. When EMC characteristics are known, the need for and extent of EMC testing can be determined by a review of those characteristics.
Knowing specific target frequencies, EMC testing can focus on the aircraft systems (and even those susceptible frequencies in the case of tunable systems) likely to be affected by interference. Where sensitive systems or potentially strong sources of EMI are involved, more intensive evaluation will be required.
TABLE 2-3. COMMONLY USED RADIO FREQUENCIES ON AIRCRAFT Range Hz Mode Function 190-1750 kHz Rx ADF Navigation 2-30 MHz Tx/Rx HF Communications 75 MHz Rx Marker Beacon Receiver 108-112 MHz Rx ILS Localizer Receiver 108-118 MHz Rx VHF Omnirange (VOR) Receiver 118-137 MHz Tx/Rx VHF Communications 243 MHz Tx Emergency Locator Xmtr (Satellite)
328.6-335.4 MHz Rx ILS Glide Slope Receiver
406.3 MHz Tx Emergency Locator Transmitter 960-1215 MHz Tx/Rx DME System 1027-1033 MHz Tx/Rx Transponder & TCAS Systems 1087-1093 MHz Tx/Rx Transponder & TCAS Systems 1575.42 MHz Rx GPS Satellite Navigation
c. On-aircraft EMC tests for systems or equipment should be conducted. If lab test data is available it should be used to guide the planning of these tests. If lab test analysis is not available a more comprehensive EMC testing on the aircraft systems and equipment typically needs to be performed.
(1) The aircraft should not be close to large reflecting surfaces such as buildings or other Par 209 Page 20
aircraft. Use of ground power is not recommended, as ground power units are not routinely checked for output quality.
(2) All normally closed circuit breakers should be closed and power should be supplied to all normally powered AC and DC distribution busses during testing.
(3) The aircraft should be in flight configuration. Doors and hatches that might be in any interfering signal’s path should be in the position they would normally be in during flight.
(4) Aircraft systems being tested should be operated and monitored for indication of interference. (It is essential that systems determined critical for the operation of the aircraft are tested.)
The following systems, if installed, should be included in the aircraft EMC test plan.
TABLE 2-4. AIRCRAFT ELECTRICAL AND
ELECTRONIC SYSTEMS System ADF Air Data Systems Altitude Alert System ATC Transponder Audio Distribution System Autopilot/Flight Guidance System Compass/Directional Gyro Systems DME Electronic Flight Control System Electronic Flight Instrument System (EFIS) Global Positioning System (GPS) Marker Receiver System VHF Communications
VOR/LOC/GS Newly Installed Electrical/Electronic System
210. FUNCTIONAL HAZARD ASSESSMENT (FHA).
NOTE: Refer to AC 43.1309-1 (current edition) for additional information on FHA.
a. Many older aircraft designs did not provide for all weather operations or potential increases in the pilot’s reliance on installed systems and equipment. Requirements to assure design safeguards against hazards have developed as technologies have become available and pilots have increased their reliance on installed systems and equipment. A fundamental analysis to assure design safeguards is accomplished through a functional hazard assessment.
b. Alterations that involve systems or equipment that perform critical functions or that include complex designs that have a high degree of integration, use of new technology, or novel applications of conventional technology, must be assessed to determine th e severity of failure conditions. Complexity in itself does not drive the need to perform a system safety analysis but the effect of a failure does. Comparison with similar, previously approved systems is sometimes helpful.
c. Evaluate the system to determine if it is essential or not essential to safe operation. For aircraft of 6,000 pounds or less maximum weight, refer to the regulations incorporated by reference in the type certificate, unless the Administrator has found that the change is significant in an area.
d. Determine if the equipment has any unacceptable, adverse affect when operated.
e. Determine if the operation of the installed equipment has an adverse affect on equipment not essential to safe operation, and if a means exists to inform the pilot of the effect.
f. Determine if a failure or malfunction of the installed equipment could result in unacceptable hazards.
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g. Design requirements and methodology of hazard resolution differing upon application and type of aircraft (i.e., single-engine, multiengine, commuter use).
(1) Operation of equipment that has an adverse effect on other equipment essential to safe operation of the aircraft is unacceptable.
(2) Operation of equipment that has an adverse effect on other equipment that is not essential to safe operation of the aircraft may be acceptable if there is a means to inform the pilot of the effect.
(3) If a probable failure or malfunction will result in a hazard in a multiengine aircraft it is unacceptable.
(4) If a probable failure or malfunction will result in a hazard in a single-engine aircraft its impact must be minimized.