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2.5.2 Table 2-2 is an example of determining the static test loads for a 7-pound piece of equipment to be installed in a utility category aircraft (14 CFR part 23).
Table 2-2. Sample Load Factors Load Factors (From the Above Table) Static Test Loads (Load Factor x 7 Pounds) Sideward 1.5g 10.5 pounds Upward 3.0g 21.0 pounds Downward 6.6g 46.2 pounds Forward 9.0g 63.0 pounds
2.5.3 When an additional load is to be added to a structure already supporting previously installed equipment, determine the capability of the structure to support the total load (previous load plus added load). If the additional load requires access to applicable design data or the capability to reverse engineer the installation, further assistance may be required from FAA engineering, the responsible Aircraft Certification Service office, or an appropriately rated Designated Engineering Representative (DER).
2.6 Static Tests.
CAUTION: The aircraft or equipment, or both, can be damaged in applying static loads, particularly if a careless or improper procedure is used. It is recommended, whenever practicable, that static testing be conducted on a duplicate installation in a jig or mockup that simulates the related aircraft structure. Static test loads may exceed the yield limits of the assemblies being substantiated and can result in partially sheared fasteners, elongated holes, or other damage that may not be visible unless the structure is disassembled. If the structure is materially weakened during testing, it may fail at a later date. Riveted sheet metal and composite laminate construction methods especially do not lend themselves to easy detection of such damage. To conduct static tests:
2.6.1 Determine the weight and center of gravity (CG) position of the equipment item.
2.6.2 Install the attachment in the aircraft or, preferably, in a jig using the applicable static test load factors.
2.6.3 Determine the critical ultimate load factors for the sideward, upward, downward, and forward directions. A hypothetical, which follows steps 1 through 4 below, pertains to the example in Figure 2-3, Hypothetical of Determining Static Test Loads.
1. Convert the gust, maneuvering, and ground load factors obtained from the manufacturer, FAA engineer, or DER to determine the ultimate load factors. Unless otherwise specified in the airworthiness standards applicable to the aircraft, ultimate
2-5 lo ad factors are limit load factors multiplied by a 1.5 safety factor (see Figure 2-3 , columns 1, 2, and 3 for items A, B, and C).
2.
Determine the ultimate inertia load forces for the emergency landing conditions as prescribed in the applicable airworthiness standards. (See Figure 2-3, items D and E, column 3.)
3. Determine what additional load factors are applicable to the specific seat, litter, berth, or cargo tiedown device installation. The ultimate load factors are then multiplied by these factors to obtain the static test factors.
4. Select the highest static test load factors obtained in steps 1, 2, and/or 3 for each direction (sideward, upward, downward, and forward). These factors are the critical static test load factors used to compute the static test load (see Figure 2-3, column 6).
2.6.4 Apply a load at the CG position by any suitable means to demonstrate that the attachment and structure are capable of supporting the required loads. When no damage or permanent deformation occurs after 3 seconds of applied static load, the structure and attachments are acceptable. Should permanent deformation occur after 3 seconds, modifications or reinforcements to the affected structure are required. Additional load testing is not necessary.
2.6.5 Static tests may need to be reviewed by an FAA engineer so that appropriate limitations, procedures, checks, and balances may be applied to mitigate any risks.
2.7 Materials and Workmanship. Use materials conforming to an accepted government or industry standard such as Army/Navy and Air Force/Navy (AN) National Aerospace Standards (NAS), Technical Standard Orders (TSO), or Military Specifications (MIL-SPEC).
2.7.1 Suitability and durability of materials used for parts, the failure of which could adversely affect safety, must:
• Be established by experience or tests;
• Meet approved specifications that ensure the strength, and other properties, assumed in the design data; and
• Take into account the effects of environmental conditions, such as temperature and humidity, expected in service.
2.7.2 Workmanship must be of a high standard.
2.8 Material Strength Properties and Design Values. Material strength properties must be based on enough tests of material meeting specifications to establish design values on a statistical basis, such as Metallic Materials Properties Development and Standardization (MMPDS), available at https://www.mmpds.org/. Design values must be chosen to minimize the probability of structural failure due to material variability. Except as provided in paragraph 2.8.5 below, compliance with this paragraph must be shown by selecting design values that ensure material strength with the following probabilities:
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2.8.1 Where applied loads are eventually distributed through a single member within an assembly, the failure of which would result in loss of structural integrity of the component―99 percent probability with 95 percent confidence.
2.8.2 For redundant structure, in which the failure of individual elements would result in applied loads being safely distributed to other load carrying members―90 percent probability with 95 percent confidence.
2.8.3 The effects of temperature on allowable stresses used for design in an essential component or structure must be considered where thermal effects are significant under normal operating conditions.
2.8.4 The design of the structure must minimize the probability of catastrophic fatigue failure, particularly at points of stress concentration.
2.8.5 Design values greater than the guaranteed minimums required by paragraph 2.8 may be used where only guaranteed minimum values are normally allowed (e.g., if a “premium selection” of the material is made in which a specimen of each item is tested before use to determine if the actual strength properties of that particular item are equal or exceed those used in design).
2.9 Fasteners. Use hardware conforming to an accepted government or industry standard such as AN, NAS, TSO, or MIL-SPEC. Attach equipment in such a way that prevents loosening in service due to vibration.
2.9.1 Each removable fastener must incorporate two retaining devices in case one retaining device should fail during flight operations.
2.9.2 Fasteners and their locking devices must not be adversely affected by the environmental conditions associated with the particular installation.
2.9.3 No self-locking nut may be used on any bolt subject to rotation in operation unless a nonfriction locking device is used in addition to the self-locking device.
2.10 Protection of Structure. Provide protection against deterioration or loss of strength due to corrosion, abrasion, electrolytic action, or other causes. Each part of the structure must:
2.10.1 Be suitably protected against deterioration or loss of strength in service due to any cause, including:
• Weathering,
• Corrosion, and
• Abrasion.
2.10.2 Have adequate provisions for ventilation and drainage.
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2.11 Accessibility. Provide adequate provisions to permit close examination of equipment or adjacent parts of the aircraft that regularly require, among other services, inspection, adjustment, and lubrication. For each part that requires maintenance, inspection, or other servicing, appropriate means must be incorporated into the aircraft design to allow such servicing to be accomplished.
2.12 Effects on Weight and Balance (W&B). Ensure that the altered aircraft can be operated within the weight and CG ranges listed in the FAA type certificate (TC), data sheet, or Aircraft Listing Aircraft Specification. When adding items of mass to the aircraft, the effect on the empty W&B should be considered and documented in the aircraft W&B.
Determine that the altered aircraft will not exceed maximum gross weight. If applicable, correct the loading schedule to reflect the current loading procedure. Refer to AC 43.13-1, Acceptable Methods, Techniques, and Practices―Aircraft Inspection and Repair, for W&B computation procedures.
2.13 Effects on Safe Operation. Install equipment in a manner that will not interfere with or adversely affect the safe operation of the aircraft (controls, navigation equipment operation, etc.).
2.13.1 The factor of safety prescribed in 14 CFR § 23.303 must be multiplied by the highest pertinent special factors of safety prescribed in 14 CFR §§ 23.621 through 23.625 for each part of the structure where strength is:
• Uncertain,
• Likely to deteriorate in service before normal replacement, or
• Subject to appreciable variability because of uncertainties in manufacturing processes or inspection methods.
2.13.2 Unless otherwise provided, a factor of safety of 1.5 must be used.
2.14 Controls and Indicators. Locate and identify equipment controls and indicators so they can be operated and read from the appropriate crewmember position.
2.15 Placarding. Label equipment requiring identification and, if necessary, placard operational instructions. Amend W&B information as required. Any required placards installed or required by an alteration must be added to the “Limitations” section of the instructions for continued airworthiness (ICA) to ensure that maintenance personnel will know if a required placard is missing in future inspections.
2-8 Figure 2-3. Hypothetical of Determining Static Test Loads Utility Category Aircraft (14 CFR Part 23) Type of Load Direction Load Factors 1 Limit 2 x Safety 3 = Ultimate 4 x Special 5 Static = Test 6 Critical Static Test A. Maneuvering Fwd (None) - - - Down 6.2g 1.5 9.3g - 9.3g 9.3g Side (None) - - - - Up -3.8g 1.5 -5.7g - -5.7g 5.7g Aft 1.0g 1.5 1.5g - 1.5g B. Gust (= 30 FPS @ KVc) *For locations aft of fuselage Sta. 73.85.
Fwd (None) - - - - Down 6.0g 1.5 9.0g - 9.0g Down* 6.4g 1.5 9.6g - 9.0g *9.6g Side 1.6g 1.5 2.4g - 2.4g 2.4g Up -2.8g 1.5 -4.2g - -4.2g Aft (None) - - - - C. Ground Fwd 6.6g 1.5 9.9g - 9.9g 9.9g Down 4.0g 1.5 6.0g - 6.0g D. Ultimate Inertia Forces for Emergency Landing Condition (14 CFR § 23.561).
**For separate cargo compartments.
Fwd Already Prescribed as Ultimate
9.0g - - Fwd** 4.5g - - **4.5g Down (None) - - Side 1.5g - 1.5g Up -3.0g - -3.0g Aft (None) - -
2-9 Utility Category Aircraft (14 CFR Part 23) Type of Load Direction Load Factors 1 Limit 2 x Safety 3 = Ultimate 4 x Special 5 Static = Test 6 Critical Static Test E. Ultimate Inertia Forces for Emergency Landing Condition For Seat, Litter, and Berth Attachment to Aircraft Structure (14 CFR § 23.785).
Fwd Already Prescribed as Ultimate
9.0g 1.33 12.0g 12.0g Down (None) - - Side 1.5g 1.33 2.0g Up -3.0g 1.33 -4.0g Aft (None) - - Note: Asterisks (*) denote special load conditions for the situation shown.
3-1 CHAPTER 3. COMMUNICATION, NAVIGATION, AND EMERGENCY LOCATOR
TRANSMITTER SYSTEM INSTALLATIONS
3.1 Purpose. This chapter describes installation considerations and requirements for basic standalone, installations of communication, navigation, and emergency locator transmitter (ELT) equipment.
Note: Standalone installations do not depend on other systems or complex interfaces to function.
3.2 Hazards and Warnings.
3.2.1 When installing these systems, follow the aircraft and equipment manufacturers’ instructions, as appropriate. Practice a “clean as you go” philosophy, which entails maintaining cleanliness and order. Ensure that equipment and systems function properly and perform their intended function(s).
3.2.2 Alterations of aircraft that are performed to accommodate the installation of radio equipment must be evaluated for their impact on aircraft design and operation. Refer to AC 23.1309-1, System Safety Analysis and Assessment for Part 23 Airplanes, for additional information concerning the evaluation for equipment, systems, and installations in 14 CFR part 23 airplanes.
3.2.3 Frequently, an alteration to accommodate the installation of radio equipment will have little impact on the design or operation of an aircraft; however, all potential elements of impact must be considered. One approach is to evaluate each element independently.
3.2.4 Consider the impact when Weight and Balance (W&B) or structural load limits of an added system exceeds existing installations. Consider the impact when radio frequency, such as electromagnetic interference (EMI), High Intensity Radiated Fields (HIRF), or lightning, may negatively affect existing systems (e.g., accuracy of the magnetic compass).
3.2.5 When evaluating elements of impact, consider the before and after states. No further analysis of W&B may be required if an object of similar size and weight was previously installed in a location. If mounting attach points were previously substantiated to support a specific load and the same load or less is being installed, the previous analysis may be referenced.
Note: Data that is referenced must be available and reviewed.
3.2.6 When structures must be fabricated or reinforced, the standard practices approved for repairs, if applicable, may be employed. AC 43.13-1, Acceptable Methods, Techniques, and Practices—Aircraft Inspection and Repair, may provide structural design data for fabrication of mountings and attachments.
3.2.7 Ensure that the capacity of the aircraft’s charging system is not exceeded, including any required additional allowances.
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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)