So Let's replace a wire on a engine.
We had a circuitbreaker popped on the flightdeck. After some investigation from the previous shift, they found that a electrical wire had been chafing against a metal bracket inside a engine. The vibration in engines can cause damage to wires.
Wires can be repaired depending on the damage, our wire had been chafed all the way through the insulation (hence the popped circuitbreaker) so this wire needs to be either repaired with a splice wich on the engine means a 500 flighthours maximum time limit before the wire must be replaced.
This time there is room in the timeschedule for maintenance so the operator decides to replace the wire now.
The previous shift had removed most of the wire from the wire loom (wire bundle) all the way from the engine disconnect
(a place where the engine is disconnected from the aircraft) to the upper part of the pylon (where the wiring goes into the wing - a pylon is the structure that holds the engine).
They had also routed the new wire from the engine disconnect to up in the pylon. This is where we take over the job.
My colleague starts to connect the bottom part of the wire while I go to the pylon to finish up the routing there.
The panels that are lying off are where the wire is routed through, the new wire goes into the loom that the damaged wire came out of. I need to disconnect the connectors from the wing disconnect (wich are inside the pylon and this is where the top end of our wire should end.
This sounds easy but like most things in aviation maintenance, this can be deceiving. Access is mostly against us and this time is no exception.
Right, now we know that we cannot reach it from the top nor the bottom so like most times a creative solution should be found.
These connectors are lockwired, we need to remove that lockwire and then we need to put some connector pliers on the connector to untighten it to be able to release it.
In order to do all this we should first make space for access so we get started.
First we remove the pneumatic duct that comes from the engine and feeds the pneumatic system.
This is relatively easy as the clamps for the duct are all quite accessible for us.
We then move the pneumatic duct aside so that we have some access space around the connectors.
Now with the pneumatic duct away we have some more space to play with but it's still not enough. We need to get to the connector all the way in a corner so another connector should be removed first before we can access the one that we need.
First we remove all the so called P-clips that hold the wire looms in place and keeps the wires from moving and chafing against structure or other wires.
Yes, the yellow wire loom is in the way of the wire loom that we need to replace the wire in so it has to be disconnected. U can see that the pneumatic duct is just opened, we blank those holes off so that dirt cannot get into the system.
We manage to undo the locking wire from the connector and we undo the connector from the yellow wire loom for access, the wire loom with the damaged wire is now reasonably accessible. We manage to get some angled connector pliers on the connector and we undo this connector too.
Now we have the two connectors disconnected and out of the pylon to work on the damaged wire.
The black sleeve on the connector is called a boot, it prevents moisture getting into the the backside of the connector and also provide's a strain relief on the pin's on the ends of the wires.
We need to cut that boot off to get access to the damaged wire. When we have access to the damaged wire we push (or pull depending on the type of connector) the pin (or socket) out of the connector with a extraction tool.
Now that we have the wire out of the loom completely we continue the routing of the new wire into the wire loom, we refer ofcourse to the maintenance manual wich prescribes exactly what needs to be done when u are replacing a wire into a loom.
With this information we find the partnumber for the pin that we need and the partnumbers for the tools required to shrink that pin onto the new wire.
First we find our pin from the avionic's store.
We got the partnumber of the pin from the manuals, we are looking for a standard pin but with a rather large wire size barrel for awg 16 wire.
And here it is.
We take this pin with us to the aircraft and on the way we pick up our crimping tool set wich we are going to use to crimp the pin onto the wire.
The manual tells us the tools to use and at wich setting to use them for a particular wire and pin/socket combination.
Believe me when I say that this is an expensive tool.
Now that we have the tools and the equipment to do the job, we go up onto the wing again and strip the new wire to the right length.
Then we crimp the pin onto the wire.
and connect the wire back into the connector using a insertion tool.
After that I inspect the connector.
Good, now we need to reinstall a boot onto the connector (the previous one was cut off).
Once again we go to the manuals to find the proper procedure. First we apply glue on the boot and then we shrink the boot on the connector and wire loom using a heat gun.
This is what it looks like when it's shrunk down, the two holes in the boot are there to allow for a sealing compound to be inserted into the boot.
The loom is almost complete, now we need to tie lace the loom up so that it's tight and neat.:
Now we connect the connectors back onto their receptacles and at this time I make a handover for the next shift to come on to finish up on this job.