Safety Wire Practical Test: Double-Twist and Turnbuckles

October 18, 2026 · Based on FAA-S-ACS-1, FAA AC 43.13-1B, and FAA Order 8900.1

Safety wire practical test preparation should end with an installation you can inspect, not just a definition you can repeat. For O&P study, use suitable training hardware and review the finished work with your instructor. The ACS skill is installing safety wire on nuts, bolts, and turnbuckles.

FAA-S-ACS-1, p. 7

What does safety wiring demonstrate at the O&P?

ACS element AM.I.E.S1 calls for installing safety wire on nuts, bolts, and turnbuckles. The actual project and its associated questions come from the assigned test. FAA Order 8900.1 says you must complete the project to the required performance standard and accomplish the skill demonstration on the first attempt. This guide does not promise a particular fixture or bolt count.

FAA-S-ACS-1, p. 7 · FAA Order 8900.1, Vol. 5, Ch. 5, Sec. 11, p. 16

On the test and in real work, follow the manufacturer’s instructions or other acceptable data that applies. On the test, the DME explains the task you must perform; Order 8900.1 says the examiner should not hand you the specific tools and data but should evaluate whether you can select them. The study examples below do not establish aircraft-specific limits or replace the assigned procedure. AC 43.13-1B is not blanket permission to replace manufacturer instructions: its FAA description limits the cited methods to their stated applicability, including the absence of manufacturer repair or maintenance instructions. The ACS safety appendix lists wearing safety glasses among the safety precautions the evaluator ensures you follow, and it says any disregard for safety will result in a failure.

FAA-S-ACS-1, p. A-3 · FAA Order 8900.1, Vol. 5, Ch. 5, Sec. 11, p. 16 · FAA AC 43.13-1B Active status and applicability

How do you start a double-twist installation?

First check that the units are correctly torqued and the wiring holes are aligned. AC 43.13-1B says never to overtorque or loosen a fastener just to align the holes. Safetying is not a means of obtaining or maintaining torque. If the holes will not align within the specified torque limits, the AC says washers may be used or another bolt tried.

AC 43.13-1B, p. 7-20 · AC 43.13-1B, p. 7-18

Choose the wire and pattern required for the application. The AC says not to use stainless steel, Monel, carbon steel, or aluminum alloy safety wire on emergency mechanisms; some emergency devices require brass or soft copper shear safety wire. The AC describes double-twist and single-wire methods, with the latter used for closely spaced or closed geometrical patterns. The number of fasteners that can be wired together depends on the application.

AC 43.13-1B, p. 7-18 · AC 43.13-1B, p. 7-20

Route the wire so it prevents the part’s tendency to loosen. Keep the loop close to the contour of the unit. Pull the wire taut while twisting and maintain light tension when secured; do not overstress it. The AC says safety wire twisted too tightly will break under vibration.

AC 43.13-1B, p. 7-20 · AC 43.13-1B, p. 7-21

The hand-twisting illustration in AC Figure 7-3a shows 6 to 8 twists per inch. Use that as the figure’s illustrated guidance, not a replacement for the wire and installation requirements in the applicable aircraft data.

AC 43.13-1B, p. 7-19 · FAA AC 43.13-1B Active status and applicability

How should you approach safety wire on three bolts?

For a three-bolt training fixture, plan the complete route before cutting wire. Identify the loosening tendency of each fastener, then inspect each span and each loop after installation. These steps are our rehearsal method, not an FAA procedure. Three bolts alone do not tell you which method, routing, or wire size the assigned application requires.

Compare the specified arrangement with AC 43.13-1B Figure 7-3. Do not infer that a triangular group automatically requires a double-twist chain: the AC also describes the single-wire method for closed patterns, including a triangle. Use the specified pattern for the actual assembly.

AC 43.13-1B, p. 7-18 · AC 43.13-1B, p. 7-20

What should you check when using safety wire pliers?

When using pliers, grasp the wire at the ends so the twisted section is not damaged. The AC prohibits nicked, kinked, or mutilated wire and says not to twist the wire ends off with pliers. When you cut off the ends, it says to leave at least four to six complete turns (1/2- to 5/8-inch long) after the loop. In its wire-twister procedure, the tool locks on the wire, the knob spins the rod, and squeezing the handles releases the wire. The AC adds a caution: when the wire extends 3 inches beyond the jaws of the twister, loosely wrap it around the pliers to prevent whipping and possible personal injury. Excessive twisting also weakens the wire.

AC 43.13-1B, p. 7-21

Inspect the completed installation for tightness and the intended restraint against loosening. Bend the ends under and inward toward the part so they do not leave sharp projecting ends. A neat-looking twist does not excuse an incorrect route or damaged wire.

AC 43.13-1B, p. 7-20 · AC 43.13-1B, p. 7-21

How is safety wire on a turnbuckle different?

Use the turnbuckle procedure rather than transferring a bolt-head pattern to the barrel. AC 43.13-1B describes double-wrap and single-wrap methods and says not to reuse safety wire. After adjustment to correct cable tension, no more than three cable threads are to be exposed on either side of the barrel. Select wire material and size for the application using the applicable data and the AC’s Table 7-8.

AC 43.13-1B, p. 7-49 · AC 43.13-1B, p. 7-51

The AC’s double-wrap procedure uses two separate lengths of wire and finishes with wraps around the shanks. The described step calls for at least four turns of the remaining wire around the shank; follow the complete procedure and its figure for the actual terminal arrangement.

AC 43.13-1B, p. 7-50

For your next supervised rehearsal, inspect four things deliberately: correct fastener torque before safetying, restraint against loosening, undamaged wire, and protected ends. Keep that inspection separate from any spoken review using the hardware oral questions.

Related guides

• Understand the practical project
• Review hardware orally
• FAA practical test changes in 2026

Sources

FAA sources checked October 18, 2026.

• FAA-S-ACS-1
• FAA Order 8900.1, Volume 5, Chapter 5, Section 11, Administer an Oral and a Practical Test: Mechanic Applicant Under Part 65 Subpart D (CHG 929, 9/17/2024)
• FAA AC 43.13-1B Active status and applicability
• FAA AC 43.13-1B, Acceptable Methods, Techniques, and Practices: Aircraft Inspection and Repair (with Change 1)

About this guide: drafted with AI from the FAA sources listed on this page and checked claim by claim against them. Not reviewed by an A&P mechanic or DME. How we make our guides