Posted on April 6, 2026 Tony Adams
Securing fasteners in critical aerospace assemblies like engine manifolds, landing gear, and flight control linkages is an imperative safeguard against thermal cycling and vibration-induced loosening. Lockwire, also known as safety wire, has served as the industry standard for keeping fasteners in place for decades. However, in recent years, safety cable systems have become increasingly prevalent for serving the same function with far better repeatability. To help you determine the best option for your maintenance tasks, this blog will examine why safety cables are gaining favor over lockwires in aerospace applications.
Remaining in service across military, commercial, and general aviation platforms thanks to its simplistic design, a lockwire is a malleable metal wire that requires only pre-drilled fastener heads to be used. After being threaded through, pliers are used to twist the wire in place so that any tendency for the fastener to rotate in the loosening direction increases tension in the wire. Importantly, the number of twists per inch are strictly determined by aircraft maintenance manuals and regulatory guidance.
The most common lockwire materials in aerospace settings include:
Additionally, they come in widths ranging from approximately 0.020 inch to 0.041 inch to fit certain fastener diameter and application requirements.
Like lockwire, safety cables are meant for use with fasteners featuring drilled heads or cross-holes. However, instead of being manually twisted, safety cable assemblies use a calibrated installation tool to tension them and secure a ferrule on the end that locks them in place.
Rather than a single wire, these components have multiple strands of high-grade stainless steel or Inconel cables that are braided together. In addition to various diameter options, most ranging from 0.020 to 0.062 inches, aerospace safety cable systems also come in diverse cable lengths and strand configurations.
At the start of installation, users are meant to thread the plain end of the cable through the first fastener until the cap hits the head. Because the cap's diameter is larger than the drilled hole, it creates a mechanical stop that cannot be pulled through.
Once the cable has been routed through the designated series of fasteners, a hollow cylindrical ferrule is used. Ferrules are either supplied as loose pieces in a coordinated kit or housed in bulk cartridges for rapid loading into the installation tool. When using an individual ferrule, the technician slides it over the cable until it sits flush against the fastener. For loaded ferrules, the bare wire is inserted into the tool's nose, which automatically positions the ferrule onto the cable as it engages.
The completion of the system relies on a calibrated pneumatic or manual pull-tool that must be positioned flush against the ferrule and the fastener face. The tool’s internal mandrels grip the bare end of the cable and retract it through the tool body, drawing all remaining slack out of the assembly and tensioning the entire run to a specific, pre-set force. In one continuous motion, the tool then compresses or swages the ferrule onto the cable to lock in the tension and shears the excess wire flush with the edge.
Despite its reliability, lockwire installation depends heavily on technician skill. Variability in twist rate, routing direction, and termination technique can introduce uneven tension, noncompliant twist spacing, or sharp wire ends, all of which can necessitate rework or raise inspection concerns. These practical limitations have contributed to the aerospace industry’s growing interest in alternative systems.
The major advantage of safety cable systems is their engineered repeatability. Because installation is controlled by a tool, the results are highly uniform from one fastener set to another. This reduces the likelihood of:
In addition to better consistency, the multi-strand construction of safety cables distributes load across several strands for far more robust fatigue resistance. Although both safety cables and lockwires are intended to prevent fastener rotation as opposed to bearing primary structural loads, the form of safety cables offers additional assurance under the constant vibration and other dynamic stressors that occur during flight.
Because a safety cable tool tensions, crimps, and trims the cable in a single sequence, technicians can complete installations far more quickly and with fewer manual adjustments. This improved efficiency is particularly valuable in high-volume or line maintenance operations, where facilitating shorter turnaround intervals without cutting corners is highly desirable. While the reduced installation time for one assembly may be somewhat insignificant on its own, using these components over time can accumulate to measurable cost savings for operators and MRO facilities.
In summary, while traditional lockwire has not been universally phased out, many operators have opted to incorporate safety cable into their maintenance programs for its layered benefits. So long as their use is authorized by the aircraft manufacturer and documented in approved maintenance procedures, safety cable systems are a great modern alternative. For those looking to source high-quality safety wire, lockwire, fasteners, and any other components, NSN Fulfillment has you covered.
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