march2023 - 12

Industry Expert Column
Preventative Maintenance
for GPU Cables
Care should be taken when creating a PM checklist to keep
personnel safe while powering aircraft on the ground.
BY BILL STAHL
P
reventative maintenance (PM)
programs are crucial for proper
ground support equipment
(GSE) care. This applies to GSE of all
types, from belt loaders and tractors
to ground power units (GPUs) and
pre-conditioned air (PCA) units.
But PM programs are important for
GSE parts and components, too. When
it comes to GPU cables, regular preventative
maintenance is key to avoid
serious injuries to ground personnel
that use equipment with high electrical
capacities.
The Importance of PM
Programs
To extend cable life and improve the
safety of your team, a basic visual
inspection of the GPU cable should be
done every time the cable is going to
be used. Look for kinks, cracking, cuts,
drag abrasion or a scrunched jacket. For
example, after years of service, it's not
uncommon for a cable that is often used
on 737s to have a banana-like bend sloping
down the cable head. If a potential
issue is spotted, it is recommended to
perform a load bank test with a thermal
imager to check for any hot spots.
Regardless of whether a visual issue
is spotted during the inspection, load
bank tests should be scheduled quarterly
to make sure that the cable maintains
satisfactory condition. Many facilities
and GSE maintenance teams already
have a regular GPU PM schedule, so
be sure to check the GPU cable while
testing the GPU.
Socket Retention in the GPU
Cable Head
Using a proper cable test kit, the socket
retention in the cable head should also
be inspected regularly to ensure a proper
aircraft connection. According to SAE
document AIR4365A, loose cable contacts
or worn aircraft phase pins can cause
" hot plug " issues that can result in loss
of the E & F control voltage leading to
Serious employee injuries can be avoided
and expensive aircraft damage can be
prevented by taking the time to effectively
inspect GPU cables before use.
12 || Ground Support Worldwide || March 2023
the aircraft rejecting the external power.
Many times, when an aircraft rejects
ground power, the GPU is the first thing
that we troubleshoot. Often, the issue lies
within the cable assembly, specifically at
this connection point itself.
The cable head sockets should always
have enough tension to hold the cable in
place and support the weight of the cable
held off the ground. You should never
need to rely on a cable strap to hold that
tension to the aircraft receptacles. Guidance
for the acceptable tension can be
found in Military Standard MIL-C-7974,
which specifies an insertion force of 80
lbs. +/- 20 lbs. and a maximum extraction
force of 100 lbs.
It is recommended that each phase
socket (A-D) be tested with a pin gauge
tool and a tension meter. Each of these
four phases should test anywhere in
between 15 lbs. and 25 lbs. The E & F
control sockets will have a much lower
tension requirement with a minimum
of 1-3 lbs. If any phase falls short of
the minimum requirement, it is time
to replace the contact section of the
GPU cable head.
Don't Pair Contact Sections
from Different Cable Providers
The very end of the GPU cable head,
known as the contact section, sees more
wear than any other part of the cable
assembly. This is why several GPU cable
manufacturers have developed replaceable
contact sections, so that the end-user
can replace just the worn-down end, saving
a lot of money on lifecycle costs.
Do not, under any circumstance,
swap a different contact section onto
a different manufacturer's cable. Each
manufacturer has their own specially
ITW GSE
march2023

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