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Fig. 5. ‘Mode one’ failure, showing a bottom view of the receptacle housing. The clasp, at left, is attempting to completely
enter the receptacle, but it cannot, because of the button fragment lodged behind the slider.

2.2. Fuilure of the belt receptacle mechanism

Various used seat belt receptacles were purchased from an automobile salvage yard. All were
from Honda Accords from the affected range of model years (1986-91). One of the receptacles
was in a failed condition when it was removed from the used Accord at the salvage yard. That is,
this receptacle was exhibiting what the authors later termed a ‘mode 1’ failure: the clasp could be
inserted into the receptacle, but it refused to lock in place. Disassembly of the receptacle revealed
why, as shown in Fig. 5. A small fragment from the release button had fractured away from the
button and fallen into the receptacle, whereupon it became lodged in the slot along which the
slider must travel when the clasp is inserted. Since the slider is thus prevented from sliding to its
latched position, the buckle is likewise prevented from latching.
Further examination of the receptacle mechanism revealed two other potential failure mech-
anisms. A ‘mode 2’ failure, wherein a small piece of plastic from the release button gets wedged in
behind the locking slider (Fig. 6), preventing it from sliding to its unlatched position when the
release button is pressed. This is perhaps the most frightening failure mechanism, since it means
that the belt wearer is unable to unlatch the belt, no matter how hard he or she presses on the
release button.
The third failure mechanism results when a small piece of plastic from the release button becomes
lodged in such a way the locking slider cannot quite slide to its fully locked position (Fig. 7). Thus,
while the clasp can be inserted into the receptacle, seemingly latching the belt, in reality the clasp
can be removed by pulling on the belt with relatively little force.
Of course, the one element that each of these three failure modes has in common is the presence
of fractured pieces of the release button. It is ironic that the breaking away of these small pieces
does not impede the function of the release button itself. It is only when fate allows these fragments
to become lodged in just the wrong place that the seat belt mechanism fails.