EAA Sport Aviation - October 2009

Maintaining Existing Harnesses

It’s easy to overlook seat belts and harnesses during routine aircraft maintenance. However, they play a crucial role in aircraft safety and are designed to withstand tremendous loads in an accident. Any damage or wear can compromise these capabilities significantly.

When evaluating a harness, begin at the buckle or latch mechanism. It should operate smoothly and not show significant signs of wear. When the belt is under tension, the buckle should still be able to release without significant force. If the mechanism is loose or does not operate smoothly, it should be replaced.

The harness webbing is the next thing to inspect. Over time, the webbing can fray or deteriorate due to mechanical wear, UV exposure, or chemical damage. Fraying is easy to inspect for, but other types of damage can be more difficult to identify. Look for a fuzzy layer on the surface of the fabric or a warp in the weave. If one of these issues is present, the harness material needs to be repaired or replaced.

Fortunately, re-webbing seat belts and harnesses is a straightforward and relatively inexpensive process. There are a number of excellent repair facilities that can replace the latches, re-web the belt, and even switch the belt out for a new color that will match your aircraft’s current interior.

Finally, inspect the mounting points themselves. The mounting bolts and spacers should be secure and not show signs of wear.

Harness Options and Fitting

Seat belts and harnesses are typically categorized by the number of straps, or attachment “points,” in the harness.

For example, a two-point system is a simple lap belt system. This design is less than ideal because, while it prevents the occupant from being thrown from the vehicle, it creates a pitching moment for the entire, unsupported upper torso that can result in significant head trauma.

However, the “ultimate” solution is the

five-point harness system.

A better approach is the common three-point restraint system, which adds a single diagonal shoulder strap to the lap belt. Most aircraft use this design, but have a fixed shoulder strap that is separate from the lap belt and attaches to the male seat belt buckle with a locking clip. This two-piece design is necessary mainly because most aircraft do not have inertial systems.

Inertial-reel shoulder harnesses are a significant advantage because they automatically adjust to fit the occupant and remove the slack from the restraint system. Slack is one of the most common reasons that injuries occur, even when occupants are wearing seat belts. During an impact, the occupant’s body continues to move forward until the slack is

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