Premium on Safety - Issue 48, 2023 - 17
LESSONS LEARNED
the strands in the hoist cable were starting to
work loose and needed to be monitored.
The 164-foot stainless steel cable was built of
19 individual strands, each consisting of seven
0.156-inch diameter wires braided together.
An inner core of six was wrapped around a
single central strand; around that, a 12-strand
outer layer was wrapped in the opposite
direction. The manufacturer rated the cable
assembly for a maximum load of 450 pounds
Over the two days following the
crew change, the helicopter
performed about 30 hoists of
equipment and personnel. The
winch operator saw that the
condition of the cable had
continued to deteriorate, with
the strands of the outer layer
beginning to work loose from the
inner core.
and recommended a service life limit of 1,500
hoist cycles, defining a cycle as extension
and retraction of the cable's full length. This
corresponded to 264 revolutions of the winch
mechanism's drum, tallied by its counter
mechanism. ParkAir, therefore, divided
the counter reading by 264 to calculate the
number of cycles.
Over the two days following the crew
change, the helicopter performed about 30
hoists of equipment and personnel. The
winch operator saw that the condition of
the cable had continued to deteriorate, with
the strands of the outer layer beginning
to work loose from the inner core. An
attempt to correct this by " massaging and
manipulating " the cable as it wound back
onto the drum was unsuccessful, so the
crewman recommended that they perform
the manufacturer's specified conditioning
procedure to tension the cable and realign
its strands. ParkAir's senior pilot agreed to
carry this out the following morning before
any further working flights.
The conditioning procedure involved
attaching a 353-pound weighted bag to the
hook, flying to an open field near the depot,
and hovering with the bag about 16 feet above
the ground before climbing as the cable was
paid out at an equivalent rate. After the cable
was fully extended, it was reeled back in. After
they landed, the cable's condition was found
to have deteriorated further, so a second
ATSB investigation photo of the failed hoist cable.
attempt was made. This time the cable failed
under load while close to maximum extension.
The helicopter experienced only a slight tilt
as the weight was released, and no one on the
ground was hurt.
The Australian Transport Safety Bureau
(ATSB) found that the strands of the cable's
outer layer had splayed outwards due to
overload failure, while the inner core had
retracted some two to two and four-tenths
inches and remained intact. Scanning electron
17
Premium on Safety - Issue 48, 2023
Table of Contents for the Digital Edition of Premium on Safety - Issue 48, 2023
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