maintenance
& restoration
This Mooney aircraft includes an aviation inflatable restraint system
from AmSafe using the same technology as automotive air bags,
customized for aircraft use. The inflatable portion is contained within
the belt itself, and the electronics are contained within a small
control box.
taken out of the restraints. However, seat belts do not stretch,
and once the slack is taken out, the body will stop abruptly.
This sudden stoppage can cause serious internal injury.
The human body can withstand decelerations of 20g’s
without injury, and aircraft harness systems are designed to
handle this load. This means that most aircraft accidents can
be survivable assuming that the harness is fitted properly
and the occupant is securely restrained.
Both the location of belts and the lack of slack are critical
to safety. The goal is to locate belts over the strongest skeletal
parts of the body. Lap belts that are positioned too high will
cause internal injuries to the abdomen. If they are positioned
too low, they will not restrict forward movement enough to
adequately protect the occupant.
While three-point restraints are adequate, four- and especially five-point restraints are especially suited to aircraft
use. This is due to the three-dimensional forces common in
aircraft accidents. In automobiles, frontal impacts are much
more common than rollovers. In aircraft, nose-down impacts
are typical. Therefore, it’s essential that the pilot and passengers are protected in all directions.
Four-point restraint systems add a second shoulder belt,
ensuring that the occupant cannot twist past a single diagonal restraint. However, the “ultimate” solution is the five-point harness system. The five-point system has a crotch
strap that the four-point system doesn’t have. This strap is
critical because it stabilizes and “locks in” the rest of the
straps to the seat bottom. While this is less common, and not
the most comfortable in your average GA traveling machine,
it’s a must for aerobatics.
Designing Harness Systems in
Experimental Aircraft
If you are designing a harness system for your own experimental aircraft, you can mount the harness to either the
seats or the aircraft structure. Either way, there are two
critical factors to consider:
1.) Mounting Point Strength
Since we know that the human body can withstand g
loads up to 20g’s, the mounting points for the harness
system should be able to withstand more than that 20g
force. Whether you’re dealing with a steel, aluminum, or
composite structure, it’s critical that the mounting points
be securely attached to the aircraft structure and designed
to spread the load at the time of impact.
2.) Location of Mounting Points
Without proper locating of the mounting points, you will
never be able to properly adjust the harness. The location
of the mounting point should allow the lap belt to sit
directly across the upper pelvis of the occupant, regardless
of the seat position. A mounting point too far back will
cause the belt to locate too high; too far forward and the
belt will sit too low.
The mounting points for the shoulder harnesses may
be on a secondary aircraft structure. However, the mounting location should be able to withstand a 500-pound test
load. The mounting points should be within an angle of
30 degrees above the horizontal from the shoulder of the
seat occupant. It is extremely important that the shoulder straps’ mounting points be outside of the shoulders
of the occupant. If they fall too close to the occupant’s
neck, the harness could asphyxiate the occupant during
an accident.
Air-Bag Systems
One of the most significant new products with respect
to aircraft crash survivability is the aviation inflatable
restraint system (AAIR) from AmSafe. This system incorporates an air bag that is built into the seat belt itself, with
a separate inertial sensor and deployment system. AmSafe
has received supplemental type certificates for its AAIR
harnesses for a variety of general aviation aircraft. They
are even standard equipment for many new aircraft from
Cessna, Hawker Beechcraft, Cirrus Design, Diamond,
Mooney, and more.
As pilots, we work hard to avoid accidents at all cost.
However, for all the effort that we put into training to
avoid accidents, it pays to put some effort into maintaining and improving on the restraint systems that may save
our lives, and those of our loved ones, in the event that
an accident does happen.
Jeff Simon is the president of Approach Aviation, a provider of educational products, tools, and supplies for aircraft owners. To learn more about aircraft ownership and
maintenance, visit
www.ApproachAviation.com or call
877-564-4457.
