AET Aircraft Wiring Practices and Standards — Questions and Answers
Question 1: Which wire specification is the current standard for most aircraft applications due to its lightweight PTFE insulation?
- MIL-W-5086 (PVC-insulated)
- SAE AS22759 / MIL-W-22759 (PTFE-insulated) (Correct answer)
- MIL-W-16878 (general purpose)
- AWM Style 1007 (appliance wire)
Correct answer: SAE AS22759 / MIL-W-22759 (PTFE-insulated)
SAE AS22759 (formerly MIL-W-22759) uses PTFE (Teflon/Tefzel) insulation, which provides excellent heat resistance, low weight, and durability — making it the current standard for most aircraft wiring applications.
Question 2: What is the preferred method for splicing aircraft wiring according to FAA Advisory Circular 43.13-1B?
- Soldering with rosin-core solder and electrical tape
- Mechanical screw-type wire nuts
- Approved crimp splices with calibrated crimp tools (Correct answer)
- Heat-activated butt connectors from automotive supply
Correct answer: Approved crimp splices with calibrated crimp tools
Crimp splices using approved tools and correct positioners are the preferred method for aircraft wiring splices. They produce consistent, reliable connections without the risk of cold solder joints or flux contamination associated with soldering.
Question 3: What is the purpose of using shielded wire in aircraft wiring systems?
- To increase the wire's current-carrying capacity
- To allow a smaller gauge conductor to be used safely
- To protect the signal from electromagnetic and radio frequency interference (EMI/RFI) (Correct answer)
- To provide a redundant ground path for safety-critical circuits
Correct answer: To protect the signal from electromagnetic and radio frequency interference (EMI/RFI)
Shielded wire surrounds the conductor(s) with a conductive braid or foil that is grounded at one end, preventing external EMI/RFI from inducing noise into sensitive signal lines such as audio, sensor, and data bus wiring.
Question 4: According to aircraft wiring standards, what is the minimum bend radius typically required when routing a wire bundle to prevent insulation damage?
- Equal to the diameter of the largest wire in the bundle
- Three times the outside diameter of the wire bundle (Correct answer)
- Ten times the bundle diameter
- Half the bundle's overall diameter
Correct answer: Three times the outside diameter of the wire bundle
AC 43.13-1B specifies that wire bundles should not be bent to a radius less than three times the outside diameter of the bundle. Tighter bends stress the insulation and conductors, potentially causing cracks or breaks.
Question 5: When terminating aircraft wiring with a circular MS-series (MIL-DTL-38999) connector, what is the most critical requirement for the crimping operation?
- Apply between 50–100 ft-lbs of torque to ensure a gas-tight crimp
- Use the correct approved positioner and die set matched to the specific contact size and wire gauge (Correct answer)
- Any quality general-purpose ratchet crimper is acceptable if it closes completely
- A standard automotive crimper is sufficient for contacts below 20 AWG
Correct answer: Use the correct approved positioner and die set matched to the specific contact size and wire gauge
Approved crimp tool positioners and dies are engineered to produce the precise crimp geometry (height and width) required for each specific contact size and wire gauge combination. Using incorrect tooling will produce a non-conforming crimp that can fail in service.
Question 6: On an aircraft wiring diagram, a wire labeled '20AWG' indicates what about the conductor?
- The wire is rated for a maximum of 20 volts DC
- The wire insulation is 0.020 inches thick
- The conductor size is American Wire Gauge 20, indicating its cross-sectional diameter (Correct answer)
- The wire was installed during revision 20 of the aircraft wiring document
Correct answer: The conductor size is American Wire Gauge 20, indicating its cross-sectional diameter
AWG (American Wire Gauge) is a standardized system for wire conductor sizing. A higher AWG number means a smaller conductor diameter. 20AWG is a common gauge for aircraft signal and low-current power wiring.
AET Aircraft Wiring Practices and Standards
Which wire specification is the current standard for most aircraft applications due to its lightweight PTFE insulation?