Friday, December 03, 2010

Extracting One Angry Wasp

Back to work in the morning. The first thing is to finish that cable replacement task. What I'm calling the "cable" consists of both the actual wire that moves when I pull the cockpit knob, and its surrounding, what I'll call a housing or a channel. It's like the way an electrical wire is inside of its coating of insulation, except that this cable is designed to move inside its housing while the housing stays still. I am to remove and replace the cable and the housing together.

Before pulling the cable out of the airframe, I follow AME instructions and attach a thin wire to the end. The housing is made in a kind of spiral pattern, so when I tie another wire to the outside, it's resistant to slipping off, because of all the ridges. Also the end of the wire that was attached to the alternate air door is kinked from being held into its fastener for however long it has been there, so that too serves as an anchor for the wire. I attach the wire as well as I can, and push it a bit, following it along through all the clamps holding the wire bundles together along the leading edge of the wing until there's some slack just outside the fuselage. I jump back in the airplane and slowly pull on it it from the cockpit, then run outside and feed it through the tight spots to make sure it's not caught on anything, and repeat. It's not quite as difficult as I thought it would be, but the AMEs are not leaving me hung out to dry here, so I may be underestimating the amount they helped me. The original cable is now out, and its path is marked all the way by a length of lockwire. I celebrate this triumph by switching tasks for a moment, to go and borrow a hydraulic cart.

I ask at the next door hangar, and am directed to an airline hangar where they generally . They are wonderful. When they ask me where I'm parked, and I explain that I walked over, and am now going to go back and send the people with the truck to come and get it, one of their guys simply drives the cart and me back to the helicopter hangar. Aircraft maintenance people are typically incredibly generous. I'm very fortunate to be in a symbiotic relationship with this profession. (I break airplanes, so that they can be employed fixing them; they maintain airplanes, so I can be employed flying them). I'm very proud of having gone off on this mission and brought back a hydraulic cart as proposed, dampened only slightly when it turns out that they were already prepared to give us some help because our boss called them yesterday and asked nicely, in response to the AMEs reporting the lack of equipment.

My sense of triumph is further diminished when one of the AMEs looks closely at the cable we removed. It's missing something. It's missing the damage that was the reason he asked me to remove it. He does acknowledge that he asked me to remove the left one, but that doesn't change the fact that it's actually the right one that needs to come out. And that the left one has to go back in. Guided by the lockwire, the rethreading is less painful than I thought, but again I benefit from the assistance and experience of the guys.

It's back to the cockpit to prepare to remove the right one. I open a window and ask, "I have the floor all opened up here on the left. Do you need to inspect under here, or should I put it back together?" They need to inspect it anyway and may have other tasks that need it up, so I disassemble the right side of the cockpit while leaving the left in disarray. I try to keep everything neat and organized, but it degenerates into an unholy mess of carpet, kickplates, access panels and little things that go on other things, of the sort that always seem to be called "escutcheons" when I ask. I identify the correct cable in the underfloor area, wiggling the already identified portion, and continuing to cut the zip-ties and loosen the clamps that hold it into bundles of other cables. Some asymmetries of the airplane, plus bad luck about where this particular cable ends up within the bundle make this side harder to work with. And this airplane was never designed with the idea of replacing this cable. When the aircraft was built, all the cables that had to run from the engine to the cockpit were laid out along the shiny new leading edge of the wing and then twisted and clamped neatly together. Removing and replacing individual ones is like getting one wasp out of a mason jar full of angry wasps. Except that I could get one wasp out by poking a one-wasp-sized hole in the lid, then as soon as the first one climbed most of the way through the hole, quickly sliding something in to cover the hole behind it, and duct-taping it down. And wasps hurt when they sting you, but won't tear open your flesh the way badly trimmed zip-tie ends will.

I attach the wire as before and repeat the push, pull, feed, wiggle, thread sequence until the right cable is out. Now I see the damaged part they were talking about. I undo the lockwire from the old cable and hold it above my head in triumph. I get the brand new cable out of its bag and ready it to follow the lockwire back into the airframe. The first problem is that the housing doesn't have the same grooves and the wire protruding from the end is perfectly straight and unkinked. There's nothing to keep the lockwire on. I bend the end a little bit, and wrap the lockwire the best I can. Here goes. "Whatever you do," I'm warned, "Don't kink the new one."

So, there's more of the same. Greasy, sweaty, blood-flecked frustration. "They should be required to write the builders' names on airplanes," I suggest, "So you know whom to swear at." I wonder if surgeons sometimes feel this kind of hatred towards the oozing, gooey, uncooperative masses that they are expected to manipulate and suture. "How is it that you don't hate airplanes?" I ask. I am generally a patient and tolerant person, but this is maddening. They're laughing at me, but also with me, appreciating my articulation of what they know.

Eventually it takes all three of us feeding and threading and coaxing the cable through the airframe, but we get it into place. The panel hardware doesn't quite match, but the alternate air door knob is there to serve an occasional function, not to look pretty. I tighten it up.

Meanwhile the guys have had some trouble assembling hydraulic equipment that makes the cart interface with our airplane. The different shapes, sizes and colours of the hoses and connectors they are sorting through is reminiscent of a big LEGO set, except that the AMEs don't squabble over who gets the long red pieces. I can't help with that, but they ask me to replace the left pneumatic air filter after all. Even though it's only three months old, it will mess up the maintenance schedule later if it's not zero time now. I hop up on the nacelle and change it out. It's a piece of cake. I don't know if how much is the practice effect of doing the right one yesterday, and how much is by comparison with that fracking cable.

We go for dinner early because we're waiting on a part, and then after dinner go straight to the terminal to the cargo counter to collect a part that we've been promised is on the six p.m. flight. There is no six p.m. flight into here. The AME investigates. The part is coming from Texas, connecting through Vancouver, and it's on the six p.m. flight out of Vancouver, which is supposed to be here at 7:30. The cargo agent picks up the phone and asks someone what time the 7:30 flight is arriving today. We came south to get here, but obviously we're still in the north.


arcady said...

The cable and incompressible housing is exactly the same mechanism that you'd find on a bicycle. Perhaps this is one of those little bits of airplane design that dates back to its origins in a bike shop in Ohio.

Michael5000 said...

At the aviation museum near Portland you can go into a WWII Flying Fortress. This is interesting for a lot of reason, including that they are (compared to your mental picture) TINY and seem to have been slapped together from whatever was in the garage. But the control cables were the most amazing part. The wires don't/didn't have sleeves, they just ran through holes in the wood ribs of the aircraft back to the control surfaces. So if you, say, tripped and fell against the side of the plane, you would land on and move the wires that led to, say, the rudder. Yikes!

Aviatrix said...

The main control cables on my airplane don't have sleeves, either. Things that have small levers have a housing with a cable running through it, and things that are operated by large movements have a cable with pulleys going to the control.

A classmate in flight school that found naked cables freaky, but even the old B747s had them. An old timer captain told me a story involving a bored elephant in a cage with no roof and uncommanded (from the cockpit, anyways) pitch oscillations in a B747). Elephant reached up and yanked on the cables for something to do, and I guess it thought the results were fun, because it did it again.