12-13 allow possible recovery of a system that has had an over-temperature shutdown condition.
12.8.4 Annunciation. Annunciation of in-flight loss of cooling or fan monitors may not be required if shown by a safety analysis or test demonstration that a hazardous or catastrophic condition is not indicated. The safety analysis should consider the reliability of the fans, redundancies of functions, reversionary features (such as the ability to transfer critical functions), the enunciation of over-temperature and its response time, and the availability of other flight instrumentation. In some systems, cooling fans may be installed to improve the operating environment of the components and reduce the possibility of a failure condition or shutdown of the equipment. With supplementary installations, fan monitoring or additional temperature sensors may not be required. If cooling fans are needed to prevent a hazardous or catastrophic failure condition, installation of fan monitoring or other methods of determining the status of the cooling fan must be provided prior to flight.
13-1 CHAPTER 13. CARGO TIEDOWN DEVICE INSTALLATIONS
13.1 Purpose. This chapter provides data for making acceptable cargo tiedown device installations in non-pressurized areas of civil aircraft of 12,500 pounds gross weight or less. Engineering assistance is required for floor/attach fittings load analysis and material burn testing.
13.2 Hazards and Warnings.
13.2.1 Structural failure may occur if aircraft floor loading limits are exceeded.
13.2.2 Fire hazards may exist if materials do not meet flame resistant specifications.
13.2.3 Exceeding manufacturer’s Weight and Balance (W&B) limitations create unsafe flight conditions.
13.3 Installation Considerations.
13.3.1 Ensure that the altered aircraft can be operated within the permissible weight and center of gravity (CG) ranges.
13.3.2 Determine that there will be unobstructed access to all equipment and controls essential to the proper operation of the aircraft, required emergency exits, and emergency equipment.
13.3.3 Use only materials that are at least flame resistant for covering floors and webbing material. Refer to the applicable airworthiness standards for the aircraft involved to determine the required flame-resistant qualities. For aircraft in air taxi or other commercial operations, refer to the applicable operating rule for special requirements regarding fire protection, cargo bins, location of cargo with respect to passengers, cargo compartment, or aisle width.
13.4 Fabrication and Installation.
13.4.1 Cargo Tiedown Devices.
13.4.1.1 Cargo tiedown devices may be assembled from webbing, nets, rope, cables, fittings, or other material that conforms to a FAA-Parts Manufacturer Approval (PMA), Technical Standard Order (TSO), National Aerospace Standard (NAS), Army/Navy and Air Force/Navy (AN), or Military Specification (MIL-SPEC) standards. Use snaps, hooks, clamps, buckles, or other acceptable fasteners rather than relying upon knots for securing cargo.
Install tensioning devices or other acceptable means to provide a method of tightening and adjusting the restraint system to fit the cargoes to be carried.
13.4.1.2 Provide covers or guards where necessary to prevent damage to or jamming of the aircraft’s equipment, structure, or control cables.
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13.4.1.3 Straps and nets manufactured with MIL-SPEC webbing and thread must be evaluated to determine that the working load requirements are met. All tiedown assemblies are only as strong as the weakest component in the system, including the point of attachment.
Note: The owner/operator is responsible for ensuring that a basis of approval or acceptance is obtained for the tiedown device before use on aircraft. This is accomplished by providing substantiating engineering data of the devices being used, including aircraft floor load limits.
13.4.2 Structural Attachment. Commercially available seat tracks, rails, or other types of anchor plates may be used for structural attachment, provided they conform to a NAS, AN, or MIL-SPEC standard. This type of hardware permits a ready means of mounting a wide variety of quick-disconnect fittings for cargo tiedown. Typical examples of such fittings and their attachments are shown in Figures 13-1, Extruded Track, Anchor Plates, and Associated Fittings, through 13-5, Typical Cargo Tiedown Straps and Cargo Nets.
13.4.2.1 When installing these fittings, reinforce the existing floorboards or other adjacent structures, or both, to obtain the necessary load carrying capacity.
Seat tracks installed longitudinally across lateral floor beams generally require full-length support for adequate strength and rigidity between beam attach points (see Figure 13-4, Installation of Underfloor Support for Extruded Track).
13.4.2.2 Consider the inherent flexibility of the aircraft structure and install any reinforcement in a manner that will avoid localized stress concentrations in the structural members/areas. Give specific attention to the size, shape, and thickness of the reinforcement, fastener size and pattern, and the effects of any adhesives used.
13.4.2.3 Fittings used for cargo tiedown attachment need not be substantiated by static tests if it can be shown that the fitting’s rated minimum breaking strength would not be exceeded by the applicable static test loads. Existing racks, rails, or other points used for attachment may be verified by static tests, analysis, or a written statement by the aircraft manufacturer attesting to its adequacy to withstand the necessary loads.
Figure 13-1. Extruded Track, Anchor Plates, and Associated Fittings
EXTRUDED TRACK ANCHOR PLATE Light duty Medium duty Heavy duty Extruded track and anchor plates are available in several different styles and load capacities and will accommodate a wide variety of quick attachment fittings.
SINGLE PIN TYPE SINGLE PIN TYPE
HOLD DOWN FITTINGS CARGO TIE DOWN FITTINGS Adjustable These types of fittings are suitable for litter or berth attachment to the extruded track and anchor plate styles shown above.
These types of fittings are suitable for cargo tie down attachment to the extruded track and anchor plate styles shown above.
DUAL PIN TYPE CARGO TIE FITTINGS 360° Rotation Low profile These types of cargo tie down fittings are of greater capacity than the single pin types and are suitable for use with the extruded track style shown above.
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Figure 13-2. Miscellaneous Litter, Berth, and Cargo Tiedown Fittings
PAN FITTINGS SINGLE STUD FITTINGS Stud & Cargo ring Cargo ring only Stud only Round head Hex head
SINGLE STUD CARGO TIE DOWN FITTING
SINGLE STUD HOLD DOWN FITTINGS Lift to release These types of fittings are suitable for cargo tie down attachment to the single stud fittings or stud equipped pan fittings shown above.
STUD/RING These types of fittings are suitable for litter or berth attachment to the single stud fittings or stud equipped pan fittings shown above.
EYE BOLT These types of fittings are suitable for litter, berth, and/or cargo tie down attachment directly to the aircraft structure.
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13-5 Figure 13-3. Typical Attachment of Fittings to Honeycomb Structures
Figure 13-3. Typical Attachment of Fittings to Honeycomb Structures - Continued
1. Bed all inserts and spacers in a suitable potting compound.
2. Reinforcing plate.
3. Where fitting is subject to rotation, place washers on both sides and use a positive safety means.
4. (Alternate method in lieu of spacers) Undercut honeycomb, inject potting compound, and drill through when set.
5. Countersink if required for clearance or if desired for appearance.
6. Undercut all open edges of honeycomb 1/16" and seal with potting compound.
7. Honeycomb doubler.
8. Use epoxy or other suitable adhesive to attach doubler and reinforcing plates.
Figure 13-4. Installation of Underfloor Support for Extruded Track
EXTRUDED TRACK, FLOOR BEAM (Reinforce cut out as necessary to retain strength.)
UNDERFLOOR REINFORCEMENT
FLOOR BEAM DOUBLER/ATTACH ANGLE 13-6
Figure 13-5. Typical Cargo Tiedown Straps and Cargo Nets
THREE BAR TYPE SLIDE Rigging for easiest adjustment and moderate loads.
applicable When Rigging for maximum load whether slide is joggled or not.
TYPICAL NAS STRAP ASSEMBLY Available with various types of end hardware and up to 5000 capacity.
TENSIONING SLIDE Used to preload cargo tie down straps.
Handhold
CARGO BARRIER NET
CARGO TIE DOWN NET Commonly used to restrain bulky or composite cargo.
13.4.3 Load Factors.
Use the load factor established by the aircraft manufacturer for type certification as the basis for substantiating the cargo tiedown devices and attachments to the aircraft structure. Refer to the applicable operating rules for any additional load factor requirements if the aircraft is to be used for air taxi or other commercial operations.
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13.4.3.2 The critical load factors to which the installation is to be substantiated are generally available from the holder of the aircraft’s type certificate (TC).
When the TC holder is no longer active, contact the responsible Aircraft Certification Service office.
13.4.3.3 The maximum loading is a requirement to which the aircraft manufacturer must adhere. Aircraft manufacturer floor loading limitations take precedence over the load rating of the net, fitting, and tiedown devices.
13.4.4 Static Tests.
13.4.4.1 It is recommended that static testing be conducted on a duplicate installation in a jig or mockup that simulates the related aircraft structure. See paragraph 2.6 for static test information.
13.4.4.2 If the actual installation is used for static testing, inspect both the aircraft and the cargo tiedown device installation thoroughly before releasing to service.
Check all members and fittings for cracks, distortion, wrinkles, or elongated holes. Replace all bolts and threaded fittings that are not inspected by magnetic particle or other acceptable Nondestructive Testing (NDT) inspection process. Inspect riveted joints for tipped rivet heads and other indications of partially sheared rivets or elongated holes.
13.4.4.3 All cargo tiedown installations must be tested to the critical ultimate load factor. See Chapter 1, General, for computation and testing procedures.
13.4.4.4 When the cargo compartment is separated from the flight deck by a bulkhead that is capable of withstanding the inertia forces of emergency conditions, a forward load factor of 4.5 g may be used. All other applications require the use of an 18 g forward load factor.
13.4.4.5 Each cargo tiedown fitting installation must be static tested under forward, side, and up-load conditions. Individual fittings may be tested by applying a single pull of 12.6 g forward load at an angle of 18.5° up and 9.5° to the left or right (as applicable) of the aircraft longitudinal axis. For example, assuming a 5,000-pound static pull (rating of a typical tiedown fitting) is applied as described and divided by the g load factor, we find the fitting installation will be capable of restraining a 397-pound load under emergency conditions.
9 g x 1.33 = 12.0
13.4.4.6 When a cargo-restraining net or cargo container with multiple attachments is used, the static load requirements for each tiedown fitting may be divided equally between the fittings. For example, if the maximum cargo load to be carried is 1,800 pounds and 10 tiedown fittings are to be used, the static load requirement for each fitting is approximately 2,155 pounds.
13-9 Example: static load for each tiedown fitting 9 g x 1.33 x 1,800/10 = 2,154.6 Placard individual tiedowns for the maximum weight to be secured.
13.5 Operating Limitations, Loading Instructions, and Placards.
13.5.1 General. Revisions or supplements to the approved portions of the Aircraft Flight Manual (AFM) regarding markings, placards, or other operating limitations require FAA engineering approval. Submit the requested changes and supporting data to the responsible Flight Standards District Office (FSDO) for review and processing.
13.5.2 Operating Limitations and Loading Instructions.
13.5.2.1 Prepare revisions or supplements to the AFM or operating limitations, W&B records, and equipment list changes as necessitated by the installation of the cargo tiedown systems.
13.5.2.2 Provide instructions covering the installation and use of the cargo restraint system. For aircraft that require a flight manual, incorporate these instructions as a supplement. On other aircraft, provide a placard that references the appropriate instruction. In the instructions, cover such items as removal and reinstallation of seats or other equipment exchanged for cargo restraint systems, use of cargo nets, barrier nets, number and positioning of tiedown straps, maximum load for each compartment or tiedown area, permissible load per square foot, number of tiedown points allowable per foot of track, and maximum height of the load’s CG above the floor.
13.5.3 Placards: Cargo Area Placards. Install placards or other permanent markings to indicate the maximum allowable cargo load and weight per square foot limitation for each cargo area. A placard seat tracks the number of tiedown points permissible per foot of track.
Attach a permanent label or other marking on each cargo net, barrier net, and at cargo tiedowns to indicate the maximum cargo weight that the net or attachment will restrain when installed according to the loading instructions.
13.6 Airworthiness Compliance Check Sheet: Cargo Tiedown Device Installations.
13.6.1 General. Cargo tiedown device installations that are the same as those made by the manufacturer, or other installations which are already approved, may be accepted without further investigation. On other installations, the following points should be checked to determine that the installation is satisfactory.
13.6.2 Applicable Civil Air Regulations (CAR).
• CAR 3.390, Seats and Berths.
• CAR 6.355, Seats and Berths.
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13.6.3 Applicable 14 CFR References.
• Section 21.9―Replacement and Modification Articles.
• Section 23.785―Seats, Berths, Litters, Safety Belts, and Shoulder Harnesses.
• Section 23.787―Baggage and Cargo Compartments.
• Section 27.785―Seats, Berths, Litters, Safety Belts, and Harnesses.
• Section 27.787―Cargo and Baggage Compartments.
• Section 29.785―Seats, Berths, Litters, Safety Belts, and Harnesses.
• Section 29.787―Cargo and Baggage Compartments.
13.6.4 Structural Requirements.
13.6.4.1 If the aircraft structure is changed or altered, determine if the original strength and integrity of the structure is retained. (See Chapter 2, Structural Data, and 14 CFR § 23.561.)
13.6.4.2 Determine if the extent to which the modification affects the aircraft CG has been evaluated. Refer to 14 CFR § 23.1589.
13.6.4.3 If the equipment is mounted either on the existing structure or on a bracket attached to the existing structure, confirm that all of the structure (including the bracket, if used) is adequate to support the required loads. Refer to 14 CFR §§ 23.307, 23.561, 23.613, 25.307, 25.561, 25.613, 27.307, 27.561, 27.613,
29.307, 29.561, and 29.613.
13.6.4.4 Verify that the equipment is installed so that it does not adversely affect other structures (either primary or secondary).
13.6.4.5 Confirm that means are provided to permit proper inspections of the installation and related adjacent parts as components. Refer to 14 CFR § 23.611.
13.6.5 Hazards to the Aircraft or Its Occupants. Determine whether the:
13.6.5.1 Modification creates any projections that may cause injury by human impact.
13.6.5.2 Fabric used in the modification complies with flame-resistant requirements.
13.6.5.3 Modifications adversely affect the accessibility of the exits and doors.
13.6.6 Detail Design Standards. Verify the following:
13.6.6.1 If suitable materials are used in the construction, including standard fasteners, and if the method of fabrication will result in a consistently sound structure.
13-11 Refer to 14 CFR §§ 23.305, 23.603, 23.605, 23.607, 23.613, 27.305, 27.603,
27.605, 27.607, and 27.613.
13.6.6.2 That cargo tiedown devices conform to an acceptable standard.
13.6.6.3 That there are written procedures or diagrams concerning cargo equipment installation, removal, and any loading restrictions (see Figure 13-6, Example of Allowable Cargo Loading Diagram).
13.6.6.4 That written equipment serviceability requirements or instructions for continued airworthiness (ICA) are available to ensure the aircraft structure, tiedown devices, nets, fittings, and required placards remain in serviceable condition.
13.6.7 Recordkeeping. Verify whether:
13.6.7.1 A maintenance record entry has been made. Refer to 14 CFR § 43.9.
13.6.7.2 The equipment list and W&B has been revised. Refer to AC 43.13-1, Chapter 10, Weight and Balance.
13.6.7.3 FAA Form 337, Major Repair and Alteration (Airplane, Powerplant, Propeller, or Appliance), and ICA have been completed and accepted by the FAA.