I like a well-done safety-wiring job—let me be clear about that from the start. You can have my Milbar reversing safety wire pliers when you pry them from my old, gnarled hands as I sit and remember airplanes gone by. A beautiful safety wire job in a complex place, or with lots of bolts and nuts involved, is a thing of beauty, something for every airplane mechanic and builder to be proud of. However, there are times and places, usually at the end of a long day of wrenching, when all I want is for the job to be done so I can chase the last rays of sunset as I climb above the surrounding mountains. If you’ve ever safetied a constant-speed prop on a Lycoming, you know that it’s more likely you’ll be watching that sunset from the ground unless you started the job before midafternoon.
Safety wiring is a rite of passage—some would say a bloody rite of passage akin to those from more primitive warrior cultures—that all who work on airplanes are required to pass through in order to achieve a modicum of respect among the cognoscenti. That will never change—I hope! But there is another option for those times when you are just looking to get the job done, or when the location or arrangement of bolts and nuts is so complex that you’re not sure how you’re going to get the right tools into the right places at the right angles to get things secured. This option is the Safe-T-Cable tool and system, developed in the late 1980s by General Electric Aircraft Engines and sold today by Daniels Manufacturing Corporation.
You might be familiar with Daniels if you have built your own wiring harnesses for the EFIS and avionics in your airplane. DMC’s crimping tools are considered the industry standard when it comes to attaching perfect D-sub pins and sockets to all those little wires through which electrons (and your data) flow. DMC is known for precise and well-calibrated tooling and equipment, and this shows in Safe-T-Cable tools as well as all of their products.
The Safe-T-Cable system replaces traditional safety wire with a very thin cable available in .022-, .032- or .040-inch diameters. The cables come with a small pre-crimped block on one end. You feed the cable through the fastener and anchor points or between two fasteners—just as you would with safety wire. You then slip a ferrule over the other end, using a clever little dispenser so that you don’t have tiny ferrules rolling around the shop. You then feed the end of the cable through the nose of the crimping tool, wrapping the bitter end around a tensioning wheel. You turn the tension wheel until it clicks—just like setting the appropriate tightness on a modern automotive gas cap—and squeeze the handle on the tool. The squeezing action simultaneously crimps the ferrule onto the tensioned cable and snips off the excess cable flush with the end of the ferrule.
The fastener is now safetied with a properly tensioned cable and can’t go anywhere—and there was no careful twisting or messing around with proper safety wire lengths. Just as important, there is very little chance that you’ll be including a DNA sample from your blood in the workpiece!
The Safe-T-Cable system was originally developed for complex propulsion-system applications like turbine engines and rocket motors. It is also used extensively in high-end aerospace assembly and maintenance operations where exact repeatability is important. Safe-T-Cables are always tensioned precisely the same, and the ends are always the same size—something that is hard for even a team of skilled mechanics to accomplish. It is also much faster than traditional safety wiring work, especially since it rarely has to be cut off and done over (…and over…and over…and over…) until the mechanic is happy with the job. The cables are available in either stainless steel or high-temperature Inconel, and both work equally well in low temperature applications.
Safe-T-Cables in Homebuilts
In a typical Experimental, we find that the most common repetitive safety wiring is done on oil filters, oil suction screens and brake pad attachment bolts. These items come off and on for maintenance and are in places where you’ll be practicing your skills several times a year. How useful you’ll find the Safe-T-Cable system depends on how easy it is to access these spots for safety wiring and, honestly, how much you’re willing to spend for the convenience. In our sample of three RVs, a bush plane, and a little SubSonex jet, we found that the brake bolts are pretty easily done with safety wire, once you commit to laying down on the cold concrete—but it is far faster with the Safe-T-Cable. (It’s even faster with Nord-Lock washers, but that’s another story for another day.)
Oil filters are similar, although the closer the back of the engine is to the firewall, the nicer the Safe-T-Cable is to use. And when it comes to the oil suction plug, something that should be simple either way, we found the Safe-T-Cable to really shine because, for some reason, these things are always tucked in among heater ducts, control cables and engine mount tubes that make it hard to swing the safety wire twisters. But check your installation; some throttle control brackets might make it more difficult to access the anchor point for the cable.
Prop bolts are a big safety wire user, of course, whether you use a fixed-pitch or constant-speed. Fixed-pitch props usually present the bolt heads right up front and are easy to see. You generally have six bolts and safety them in pairs, and you might have to do it a couple of times on a pair to be happy with them, but they aren’t hard. Constant-speed props present a much tougher safety wire task, and doing them well is a sign of experience—and persistence! Using Safe-T-Cables on either type is essentially a no-brainer: quick and easy. You’ll save time either way, but you’ll save a lot more on the constant-speed installation. Fortunately, most people don’t do the constant-speed more than once every couple of years. Those with fixed-pitch wooden props might be tightening those bolts once or twice a year, so that’s a little more safety wiring.
If you check the reference material that comes with the Safe-T-Cable system, it shows examples of different safety challenges and how to execute them—a documentation requirement for most aerospace applications. Fortunately for those who have turnbuckles in their aircraft, the system can even be used for these devilish devices, and examples of how to do it are provided. If safety wiring bolts is an art, applying safety wire to turnbuckles is masterwork—especially so if they are buried inside an inspection hole in a wing. In our little jet, we have turnbuckles for the rudder cables tucked down inside the leg wells of the cockpit, and while they are easy to see and can be adjusted with only moderate difficulty, safety wiring them is an afternoon job. You have to do it one-handed because two arms don’t fit in the space. But it took us just five minutes using the Safe-T-Cable system—quick, easy and secure.
One final benefit: fewer stab wounds! The flexible cables aren’t stiff and sharp like regular safety wire, so you have far less chance of stabbing yourself on a bare end as happens to most mechanics on a daily basis. So at least you’ll save on Band-Aids and antiseptic.
Let’s Talk Cost
Clearly, safety wire is going to win here. You buy a can of safety wire by the pound, and I usually go through a can of .032 in a couple of years. My cans of .020 and .040 have probably been around for a decade (or more) each. So safety wire, once you buy a couple cans and a nice set of pliers, is basically free on a per-use basis. The Safe-T-Cable tool will set you back about $500 up front unless you can find a used one on the internet (like we did). The cables themselves come in a kit of 50 wires and 50 ferrules and retail for about $75 a bag. That’s $1.50 every time you pull one. Fortunately, large aerospace firms seem to surplus them now and again, and a bag can be found on eBay for between $18 and $35. If you find them for $18, buy as many as you can. That’s about 36 cents a pop—less than what you pay for an electronics D-sub pin or socket.
So yeah, the Safe-T-Cable system isn’t cheap. But once you have the tool, how expensive is it…really? If you’re a typical homebuilt owner with one airplane, you don’t do as much safety wiring in a year as you might think. Let’s say you take your brake pads off once a year to check or change them—that’s two cables a year. Oil changes—if you fly 150 hours in a year and do 50-hour changes, that’s three times, say six cables when you’re doing both filter and suction screen. So realistically, you’re just not talking about very much money in a year. You most likely spend more on coffee while working in the hangar. I bought enough $18 bags of cables to last my fleet for a decade or more and won’t think about the cost again.
Now let’s be honest—safety wire works great and a spool of it is cheap. Cheap safety wire pliers are available by the thousands in the fly-market at almost any regional or national fly-in. And while it might take a few tries, most folks get the hang of proper safety wiring after a while—and numerous attempts. Even the most experienced mechanics I know still occasionally put a sharp piece of wire through a finger though. It’s hard not to occasionally get scraped or nicked when dealing with sharp stainless! It’s still possible—but much less likely—to hurt yourself with the Safe-T-Cable system, but in the end, the bloody aspect of safety-wiring is more a nuisance than a constraint.
The truth is, you don’t have any real need for this system, except in some specific circumstances where a better design might make safety wiring more accessible and easier. But we all collect tools, don’t we? Fine tools are a pleasure, and specialized ones that you can use after you have finished your build are nice to have. So if you’ve already bought everything else you can think of, think again. We’re keeping the Safe-T-Cable in the inspection toolbox and will be using it whenever we can.