U.
S. Department of Transportation Federal Aviation Administration Advisory Circular Subject: Acceptable Methods, Techniques, and Practices – Aircraft Alterations Date: 7/29/26 AC No: 43.13-2C Initiated by: AFS-300 Change:
This advisory circular (AC) contains methods, techniques, and practices acceptable to the Administrator for the inspection and alteration on nonpressurized areas of civil aircraft of 12,500 pounds gross weight or less. This AC is for use by mechanics, repair stations, and other certificated entities.
Robe rt H. Reckert for Hugh Thomas Executive Director, Flight Standards Service
ii
CONTENTS Paragraph Page
Chapter 1. General1-1
1.1 Purpose of This Advisory Circular (AC)1-1
1.2 Audience1-1
1.3 Where You Can Find This AC1-1
1.4 What This AC Cancels1-1
1.5 Reference1-1
1.6 AC Feedback Form1-2
Chapter 2. Structural Data2-1
2.1 General2-1
2.2 Structural Design Process2-1
2.3 Types of Loads and Stresses2-1
2.4 Static Loads2-2
2.5 Structural Sizing and Analysis2-3
2.6 Static Tests2-4
2.7 Materials and Workmanship2-5
2.8 Material Strength Properties and Design Values2-5
2.9 Fasteners2-6
2.10 Protection of Structure2-6
2.11 Accessibility2-7
2.12 Effects on Weight and Balance (W&B)2-7
2.13 Effects on Safe Operation2-7
2.14 Controls and Indicators2-7
2.15 Placarding2-7
Chapter 3. Communication, Navigation, and Emergency Locator Transmitter System
Installations3-1
3.1 Purpose3-1
3.2 Hazards and Warnings3-1
3.3 Considerations When Installing Avionics Equipment3-2
3.4 Instrument Panel Mounting3-4
3.5 Other Mounting Areas3-5
iii
3.6 Fabrication of Supporting Brackets for Attachment to a Structure Other Than
Flooring3-7
3.7 Reinforcement of the Supporting Structure3-8
3.8 Electrical Requirements3-11
3.9 Electrical Load Analysis Procedure3-13
3.10 Electromagnetic Compatibility (EMC)3-13
3.11 Functional Hazard Assessment (FHA)3-16
Chapter 4. Antenna Installation4-1
4.1 Purpose4-1
4.2 Hazards and Warnings4-1
4.3 Additional References4-1
4.4 Structural Support4-1
4.5 Physical Interference4-2
4.6 Antenna Selection4-3
4.7 Antenna Location4-3
4.8 Antenna Bonding4-4
4.9 Electromagnetic Interference (EMI)4-5
4.10 Mechanical Installation4-5
4.11 Ground Plane Requirement (Wood/Fabric and Composite Aircraft)4-6
4.12 Antenna Feed Line Balun4-8
4.13 Antenna Repair4-10
Chapter 5. Anticollision and Supplementary Light Installation5-1
5.1 Purpose5-1
5.2 Hazards and Warnings5-1
5.3 Regulations and Other References5-1
5.4 Operational Considerations: Crew Vision5-2
5.5 Installation Considerations5-2
5.6 Markings and Placards5-2
5.7 Electrical Installation5-2
5.8 Alteration of Structure5-3
Chapter 6. Ski Installations6-1
6.1 Purpose6-1
iv
6.2 Hazards and Warnings6-1
6.3 Additional References (current editions)6-1
6.4 Installation Considerations6-1
6.5 Fabrication and Installation6-3
6.6 Rigging of Skis6-7
6.7 Documentation6-11
6.8 Flight and Handling Operational Checks6-12
6.9 Maintenance (Including Inspection)6-12
Chapter 7. Oxygen System Installations in Nonpressurized Aircraft7-1
Section 1. General7-1
7.1 Purpose7-1
7.2 Hazards and Warnings to Consider When Installing an Oxygen System7-1
7.3 Additional References (current editions)7-1
Section 2. Installation of the Oxygen System7-2
7.4 System Requirements7-2
7.5 Installation and Design Considerations7-4
7.6 Equipment Location and Mounting7-6
7.7 Thread Compound7-6
7.8 Functional Test7-6
7.9 Operating Instructions7-8
Section 3. Airworthiness Compliance Check Sheet: Oxygen System Installation in
Unpressurized Aircraft7-12
7.10 General7-12
7.11 Applicable Federal Aviation Regulations7-12
7.12 Structural Requirements7-12
7.13 Hazards to the Aircraft or its Occupants7-12
7.14 Operating Aspects7-12
7.15 Detail Design Standards7-13
7.16 Instructions for Continued Airworthiness (ICA)7-13
7.17 Recordkeeping7-14
v Chapter 8. Rotorcraft External-Load Device Installations, Cargo Slings, and External Racks ... 8-1
Section 1. General8-1
8.1 Purpose8-1
8.2 Hazards and Warnings8-1
8.3 References8-1
8.4 Installation Considerations8-1
8.5 Fabrication and Installation8-2
Section 2. Cargo Racks8-11
8.6 General8-11
8.7 Fabrication of Cargo Racks8-11
8.8 Static Test8-11
8.9 Supplemental Flight Information8-11
Chapter 9. Glider and Banner Tow-Hitch Installations9-1
9.1 Purpose9-1
9.2 Hazards and Warnings9-1
9.3 References9-1
9.4 Installation Considerations9-1
9.5 Fabrication and Installation Procedures9-1
9.6 Structural Testing9-3
9.7 Angles of Tow9-3
9.8 Placards9-4
9.9 Installation Procedures―Types of Hitches9-4
9.10 Tow Release Mechanism9-6
Chapter 10. Shoulder Harness Installations10-1
Section 1. General10-1
10.1 Purpose10-1
10.2 Hazards and Warnings10-1
10.3 Additional References10-1
10.4 Installation Methods10-1
10.5 Restraint System Configurations10-3
10.6 Advantages of Different Configurations10-3
vi
10.7 Manufacturing Standards10-4
10.8 Compliance With Standards10-4
10.9 Materials10-5
10.10 Parts Produced by Owners/Others10-6
Section 2. Geometry and Attachment10-8
10.11 General10-8
10.12 Mounting Configurations10-8
10.13 Belt Length10-8
10.14 Attachment Geometry10-8
10.15 Area and Angle Deviations10-15
10.16 Structural Attachment10-15
Section 3. Static Strength and Testing10-21
10.17 Proof of Compliance10-21
10.18 Load and Distribution―Airplanes10-21
10.19 Load and Distribution―Normal Category Helicopters10-22
10.20 Demonstrating Static Loads10-22
Section 4. Installation and Inspection Checklists10-26
10.21 General10-26
Chapter 11. Aircraft Battery Installations11-1
Section 1. General11-1
11.1 Purpose11-1
11.2 Hazards and Warnings: Handling Precautions11-1
11.3 Additional References (current editions)11-1
11.4 Location Requirements11-1
11.5 Aircraft Storage Battery Design and Installation11-2
11.6 Duplication of the Manufacturer’s Installation11-3
11.7 Other Installations11-3
11.8 Delivery Inspection11-3
11.9 Battery Installation and Removal11-4
Section 2. Lead-Acid Battery Installations11-6
11.10 General11-6
vii
11.11 Battery Box11-6
11.12 Securing the Battery11-6
11.13 Sump Jar11-6
11.14 Venting11-7
11.15 Drains11-8
11.16 Electrical Installation11-8
11.17 Quick Disconnect11-10
11.18 Weight and Balance (W&B)11-10
Section 3. Nickel-Cadmium Battery Installations11-11
11.19 General11-11
11.20 Electrical Analysis11-11
11.21 Maintenance Considerations11-11
11.22 Structural Requirements11-11
11.23 Isolation of Battery Case11-12
11.24 Ventilation11-12
11.25 Preinstallation Requirements11-12
11.26 Nickel-Cadmium Battery Installation11-13
11.27 Securing the Battery11-13
11.28 Quick Disconnect11-13
11.29 Voltage and Current Regulation11-14
11.30 Weight and Balance (W&B)11-14
Section 4. Battery Installation Checklist11-15
11.31 Structural Requirements11-15
11.32 Hazards to the Aircraft and its Occupants11-16
11.33 Operating Aspects11-16
11.34 Detail Design Standards11-16
11.35 Recordkeeping11-17
Section 5. Instructions for Continued Airworthiness11-18
11.36 Lead-Acid Batteries11-18
11.37 Nickel-Cadmium Batteries11-19
viii
Chapter 12. Adding or Relocating Instruments12-1
12.1 Purpose12-1
12.2 Hazards and Warnings12-1
12.3 Additional References12-1
12.4 Preparation12-1
12.5 Installation12-3
12.6 Testing, Marking, and Placarding12-9
12.7 Electronic Display Instrument Systems or Electronic Display Indicators12-11
12.8 Environmental Conditions12-12
Chapter 13. Cargo Tiedown Device Installations13-1
13.1 Purpose13-1
13.2 Hazards and Warnings13-1
13.3 Installation Considerations13-1
13.4 Fabrication and Installation13-1
13.5 Operating Limitations, Loading Instructions, and Placards13-9
13.6 Airworthiness Compliance Check Sheet: Cargo Tiedown Device Installations13-9
Chapter 14. Larger Tire Installations14-1
14.1 Purpose14-1
14.2 Hazards and Warnings14-1
14.3 Additional Reference (current editions)14-1
14.4 Installation Considerations14-2
14.5 Flight and Ground Handling Operational Checks14-4
14.6 Testing the Modification14-6
14.7 Maintenance (Including Inspection)14-7
14.8 Interchanging of Skis and Wheels14-9
14.9 Documentation14-9
14.10 Summary of Considerations for Approval of Larger Tire Installation (may be
used as a job aid)14-9
ix List of Figures
Figure 2-1. Bending of a Beam2-2
Figure 2-2. Typical Load2-3
Figure 2-3. Hypothetical of Determining Static Test Loads2-8
Figure 3-1. Force Diagram Normal-Utility Category3-3
Figure 3-2. Typical Fabricated Panel Mounting3-3
Figure 3-3. Typical Layouts3-4
Figure 3-4. Typical Shock-Mounted Base (Wood or Composition Flooring)3-6
Figure 3-5. Typical Shock-Mounted Base (Metal Flooring)3-6
Figure 3-6. Typical Rigid Base Plate Mount3-7
Figure 3-7. Typical Underseat Installation3-8
Figure 3-8. Typical Remote Unit Mounting Base-Vertical or Horizontal Other Than
Structure to Floor3-9
Figure 3-9. Typical Shelf Installation3-10
Figure 3-10. Typical Attachment of Support Structure to Tubular Frame Other Than
Structure to Floor3-11
Figure 4-1. Antenna Mount With Saddle4-2
Figure 4-2. Antenna Ground Plane for Nonconductive Mount4-7
Figure 4-3. One Means to Provide Adequate Antenna Bonding Through a
Composite Airframe4-7
Figure 4-4. Use Bushings for All Screws4-8
Figure 4-5. Typical Dipole Antenna Assembly4-9
Figure 4-6. Typical VOR Balun4-10
Figure 4-7. ADF Loop4-11
Figure 4-8. ADF Combined Sense Loop4-11
Figure 4-9. Communications (COM) Whip4-11
Figure 4-10. COM Whip Bent4-12
Figure 4-11. Emergency Locator Transmitter4-12
Figure 4-12. Global Positioning System4-12
Figure 4-13. Glideslope4-13
Figure 4-14. Marker4-13
Figure 4-15. Combined COM/VOR4-13
Figure 4-16. VOR Rabbit Ear4-14
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Figure 4-17. VOR Blades4-14
Figure 4-18. Transponder/DME Probe4-15
Figure 4-19. DME/Transponder Blade4-15
Figure 5-1. Typical Anticollision or Supplementary Light Installation in a Skin
Panel (Unpressurized)5-3
Figure 5-2. Typical Anticollision or Supplementary Light Installation Involving a Cut
Stringer (Unpressurized)5-4
Figure 5-3. Typical Anticollision or Supplementary Light Installation in a Fin Tip5-5
Figure 6-1. Typical Hub Installation6-3
Figure 6-2. Typical Ski Installation6-4
Figure 6-3. Typical Fuselage Fittings6-6
Figure 6-4. Main Ski at Maximum Positive Incidence (Check Cable Taut)6-7
Figure 6-5. Main Ski at Maximum Negative Incidence (Safety Cable Taut)6-8
Figure 6-6. Main Ski Incidence Angles6-8
Figure 6-7. Typical Nose Ski Installation6-10
Figure 6-8. Typical Tail Ski Installation6-11
Figure 7-1. Typical Floor Mounting7-9
Figure 7-2. Typical Baggage Compartment Mounting7-10
Figure 7-3. Typical Oxygen Installation in Light Twin Aircraft7-11
Figure 8-1. Location of Cargo Release in Relation to the Rotorcraft’s Center of Gravity8-2
Figure 8-2. Typical Cargo Sling Wiring Diagram8-5
Figure 8-3. Typical Cargo Sling Installation No. 18-6
Figure 8-4. Typical Cargo Sling Installation No. 1 (Showing Fuselage Attachment Fitting)8-7
Figure 8-5. Typical Cargo Sling Installation No. 1 (Showing Fore Aft Limiting Stops)8-8
Figure 8-6. Typical Cargo Sling Installation No. 2 (Cargo Hook Attached Directly to
Underside of Fuselage)8-8
Figure 8-7. Typical Cargo Sling Installation No. 3 (4-Leg, Cable Suspended)8-9
Figure 8-8. Typical Cargo Sling Installation No. 3 (Showing Cable Sling Leg Attachment
to Landing Gear Crosstube Fitting)8-9
Figure 8-9. Typical Cargo Sling Installation No. 3 (Showing Cargo Sling in
Stowed Position)8-10
Figure 8-10. Typical Cargo Rack Installation No. 18-11
Figure 8-11. Typical Cargo Rack Installation No. 1 (Showing Attachment Detail)8-12
Figure 8-12. Typical Cargo Rack Installation No. 28-12
xi
Figure 8-13. Typical Cargo Rack Installation No. 2 (Showing Rack Partially Installed)8-13
Figure 8-14. Typical Cargo Rack Installation No. 38-13
Figure 9-1. Glider Tow Angle9-2
Figure 9-2. Banner Tow Angle9-2
Figure 9-3. Typical Tow-Hitch Release Handle9-7
Figure 9-4. Tricycle Gear Aircraft9-8
Figure 9-5. Conventional Gear Aircraft—Leaf Spring Type Tailwheel9-8
Figure 9-6. Conventional Gear Aircraft—Shock Strut Type Tailwheel9-9
Figure 9-7. Conventional Gear Aircraft—Tubular Spring Type Tailwheel9-9
Figure 9-8. Typical TOST Hitch9-10
Figure 9-9. TOST Double Tow Rings9-10
Figure 9-10. Schweizer Type Hitch9-11
Figure 9-11. Typical Multiple Hitch for Banner Tow9-12
Figure 9-12. Typical TOST Mount for Tricycle Gear Aircraft9-12
Figure 9-13. Typical TOST Conventional Leaf Spring Mount9-13
Figure 10-1. Major Versus Minor Alterations10-3
Figure 10-2. The Three-Point Single Harness Positioning10-10
Figure 10-3. Side Mounted Single Diagonal Type Harness10-11
Figure 10-4. Acceptable Harness Mounting Areas10-11
Figure 10-5. Undesirable Horizontal Harness Positioning10-12
Figure 10-6. Undesirable Vertical Harness Positioning10-12
Figure 10-7. Ceiling Mounted Inertia Reel―Double Over-the-Shoulder Type Harness10-13
Figure 10-8. The Four-Point Independent Harnesses Positioning10-13
Figure 10-9. The Five-Point Harness Positioning10-14
Figure 10-10. “Y” Type Retractor Positioning10-14
Figure 10-11. Floor Mounted Inertia Reel―Double Over-the-Shoulder Type Harness10-16
Figure 10-12. Typical Floor Mounted Inertia Reel Installation10-16
Figure 10-13. Typical Seat Mounted Inertia Reel Installation10-17
Figure 10-14. Typical Wing Carry-Through Installation10-18
Figure 10-15. Typical Hat Section Reinforcement Installation10-18
Figure 10-16. Typical Bulkhead Reinforcement Installation10-19
Figure 10-17. Typical Stringer Section Reinforcement Installation10-19
Figure 10-18. Typical Localized Stringer Section Reinforcement Installation10-20
xii
Figure 10-19. Typical Attachments to Tubular Members10-20
Figure 10-20. Vertical Angle10-25
Figure 10-21. Horizontal Angle10-25
Figure 11-1. Typical Battery Installation in the Aircraft11-5
Figure 11-2. Typical Battery Installation With Sump Jar11-7
Figure 11-3. Battery Ventilation System11-8
Figure 11-4. Typical Battery Cutoff and Generator Alternator Control Circuit11-10
Figure 12-1. The Basic “T” Visual Meteorological Conditions (VMC)
Instrument Configuration12-2
Figure 12-2. Pressure Drop Data for Smooth Tubing12-7
Figure 13-1. Extruded Track, Anchor Plates, and Associated Fittings13-3
Figure 13-2. Miscellaneous Litter, Berth, and Cargo Tiedown Fittings13-4
Figure 13-3. Typical Attachment of Fittings to Honeycomb Structures13-5
Figure 13-3. Typical Attachment of Fittings to Honeycomb Structures – Continued13-6
Figure 13-4. Installation of Underfloor Support for Extruded Track13-6
Figure 13-5. Typical Cargo Tiedown Straps and Cargo Nets13-7
Figure 13-6. Example of Allowable Cargo Loading Diagram13-12
Figure 14-1. Diagram of Axle Height Measurement14-3
Figure 14-2. Typical Main Landing Gear Spring Strut and Axle Assembly14-8
List of Tables
Table 2-1. Ultimate Load Factors2-3
Table 2-2. Sample Load Factors2-4
Table 3-1. Typical Compass Calibration Card3-5
Table 3-2. Relationship Probabilities and Severity of Failure Conditions3-14
Table 3-3. Commonly Used Radio Frequencies on Aircraft3-15
Table 3-4. Aircraft Electrical and Electronic Systems3-16
Table 4-1. Wavelength in Feet = 984/Frequency in Megahertz (MHz)4-6
Table 6-1. Recommended Minimum Cable and Shock Cord Sizes6-5
Table 6-2. Approximate Main Ski Tension Forces6-9
Table 7-1. Typical Oxygen Duration Table7-8
Table 8-1. Cable Load Table8-3
Table 9-1. Representative Steel Cable Qualities9-7
Table 10-1. Static Test Requirements10-24