Hold Me Back

Adding shoulder belts or harnesses to older aircraft is a worthwhile investment and can be surprisingly easy.

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When I bought my Debonair from its previous owners, it had the original factory lap belts installed. As someone who had been flying airplanes equipped with three-point harnesses, it felt very exposed to be zooming around in something almost three times as fast as the car I drove to the airport but without even a shoulder strap to restrain me in the event “something” happened. One of the first upgrades I made to the plane was to add a set of four-point belts and harnesses to the front seats, and I’m happy to report I’ve never had to perform a real-world test of their effectiveness.

The Aeronca Champ I bought with a partner a couple of years back came with some kind of Rube Goldberg arrangement of belts purporting to restrain the occupant, but I’ve never been confident in them, and they actually make me reluctant to fly the airplane. Soon, they will be replaced with a system offering more comfort and at least as much restraint. If you’re still flying around with lap belts only, we strongly urge you to rethink your strategy and add some better restraints. Depending on the aircraft and your mounting options, it can be as easy as getting your mechanic to install a few bolts and making a logbook entry.

It’s Not About Turbulence

Of course, none of us are ever going to crash, right? Well, hundreds of pilots each year think that way but end up bending some sheet metal, or worse. Hopefully, their aircraft didn’t come to a sudden stop and gently decelerated instead. Because a sudden stop is the nightmare scenario when it comes to physical restraints, whether in an airplane or the car you drove to the airport.

The issue is that stuff that’s not strapped down tightly will obey Newtonian physics—a body in motion tends to stay in motion— when its container comes to a halt. That means, even if you’re wearing a lap belt, your upper body won’t be restrained when the sudden stop occurs and very likely could end up in the yoke and/or instrument panel.

Unless you’re flying something designed relatively few years ago, like a Cirrus, and even if it’s a brand-new Cessna, Piper or Beechcraft, there’s a metal panel a couple of feet in front of you. Your head will hit it in the event of that proverbial sudden stop. Meanwhile, according to NASA’s Small Airplane Crashworthiness Design Guide, “Control yoke designs that have horizontal shafts that pass through [the] instrument panel and into the aircraft crush zone should be avoided. Full-scale tests have shown that these horizontal shafts can be thrust into the occupant with great force during the impact.” In other words, the instrument panel isn’t the only thing that can hurt you.

Next time you’re in the airplane you typically fly, take a moment to position the seat as you prefer and bend forward until your head touches the instrument panel. That’s where it will impact, and whatever is there—like a glass panel, a heading bug or a toggle switch—will be what contacts your head, at a substantial velocity.

Lap belts are merely okay for restraining humans in turbulence or when something relatively soft like a seat back is the only thing to hit. When it’s a stiff piece of sheet metal, probably forming a structural part of the airplane, the outcome likely will be less satisfactory.

Choices

When adding shoulder belts to an in-service aircraft, you actually have a fairly wide range of options, and not just related to color. For example, you can go with an integrated three-point system, with a strap worn diagonally across the chest, like a modern automobile, or with a separate strap that is positioned the same way but which buckles to the seatbelt locking mechanism itself.

Four-point restraint systems will feature a strap over each shoulder, plus two lap belts, fastening to a central buckle. A five-point system adds a crotch strap, anchored to the seat, which helps prevent the lap belt from riding too high on the wearer’s torso.

Each of these types can incorporate an inertial reel that allows the shoulder straps to retract when not in use but which also locks when significant force is applied, again just like your modern car. The four- and five-point systems can be equipped with a rotary buckle that releases all belts with one quick twist, or you can opt for a more conventional metal-to-metal buckle with a latch. If you’ve ever flown in a war bird or an aerobatic aircraft, you may be familiar with the over-center-latch style of buckle, with a longish lever that tightly locks the belts down using a cam arrangement.

Mounting

When it comes to how the shoulder harness is mounted, you may not have nearly as many options as there are belt choices, however. Three-point harnesses likely will retain the factory lap belt anchor points but require a separate and relatively stout attachment to the airframe. Four/five-point harnesses typically mount their shoulder straps to the cabin roof, either to an existing structural member or to something a mechanic has to add. That can get spendy, and certainly involves partial interior removal.

Aircraft like the Champ, with steel-tube fuselages, may offer attach points for mounting brackets without even drilling a hole. If riveting, drilling or other structural work is required, along with FAA approval, it’s preferable to use an STC’d or documented previous installation in the same type of aircraft. If your aircraft’s manufacturer is still in business, they may offer a model-specific mounting kit with all the parts and drawings.

One mounting method we think you should avoid involves anchoring the shoulder straps to the seat back. This mounting usually attaches the shoulder straps to the bottom rear of the seat. Depending on the geometry, in a sudden stop they can compress the wearer’s spine, perhaps resulting in an injury that otherwise wouldn’t have happened. The sidebar below summarizes FAA policy on installing harnesses in older aircraft, and the airworthiness approvals that may be necessary.


FAA Installation Approvals

Believe it or not, the FAA actually did something right when it put forth its policy, “Methods of Approval of Retrofit Shoulder Harness Installations in Small Airplanes.” This statement, also known as Federal Aviation Administration Policy Statement Number ACE-00-23.561-01, identifies the three methods of approving a harness installation: supplemental type certificate (STC), field approval or minor alteration.

STC

“An STC is the most desirable and most rigorous approval. The STC offers the highest assurance that all of the airworthiness regulations have been met…. STC approvals are usually obtained by a shoulder harness installation kit supplier for multiple airplane installations in an airplane model or model series.”

Field Approval

“Field Approvals are appropriate for alterations that involve little or no engineering. If the installation requires structural modifications [an Aircraft Certification Office] will need to [approve] the structural aspects of the installation.

Minor Change

This approval method may be used when the installation has no appreciable effect on the aircraft’s airworthiness and typically is used when there’s no STC or field approval, and when drilling or welding is not required.


Jeb Burnside is the editor-in-chief of Aviation Safety magazine. He’s an airline transport pilot who owns a Beechcraft Debonair, plus the expensive half of an Aeronca 7CCM Champ.


This article originally appeared in the March 2021 issue of Aviation Safety magazine.

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6 COMMENTS

  1. I’d add that AmSafe, the airbag manufacturer, offers a line of STC’s for many aircraft to install their “generic” lap belt, which might be even a better choice. Airbags are now standard equipment across a wide range of aircraft. And to go one step further, BRS offers a ballistic parachute for 172’s and I think for 182’s as well.

    • “…install their “generic” lap belt..”

      Their what?

      Lap belts are rather generic.
      Combination lap-shoulder belts are common in cars, single motion to single buckle.

      Unlike the fool arrangement of early 90s which automatically positioned the shoulder belt, all the better to submarine under after user forgets to also do up the separate lap belt. Manufacturers and regulators are stoopid some days.

      A traditionally good belt arrangement was on Boeing airliners like 737, lap belt with large buckle in centre, shoulder straps plugged into it, plus crotch strap from below of wanted. (I forget if 757/767 improved on it, I was advised that it was OK for females though better desired. Much effort was put into better belts for F/As on those airplanes.)

  2. The one kind of seat belt system that you can’t get is one made of modern materials. Somewhere in the FAA vaults is a requirement for belt webbing to be made of nylon. Auto makers and related regulators discovered three decades ago that nylon belts degrade when exposed to UV light and fray rather quickly. For this and additional strength with reduced stretching, all land vehicle restraints are of woven polyester, while aviation remains codified into the world of 1960.

    Similar examples are easily found. (The head-piercing qualities of toggle switches were also discovered decades ago, which is why you won’t find them in any car built since ~1980.) Inferior products built to standards long surpassed costing 10 – 100 times as much as a modern version, cause crashes and kill people. But no bureaucrat ever got fired for saying “no”.

    • Jeff if you have a solution ready to test I would recommend contacting your local ACO office and start discussions with the FAA. Who knows maybe it is you who will bring the next level of seatbelt safety to aviation. Throwing rocks from the bleachers does little to help the players on the field.

    • Wow! I didn’t know that there is a regulation restricting safety belt manufacture to nylon! Are all the aftermarket belts also required to be made of nylon as well?
      And what I meant by “generic” in my comment was that while AmSafe sells belts for specific aircraft, such as the Cirrus that installs them in new planes, AmSafe also has a non specific to aircraft after market belt that can be installed in a wide variety of aircraft. Unlike the Cirrus, which mounts them in the shoulder harness, these are lap belts.