Monday, April 27, 2015

It's all in the name

We aircraft mechanics change a lot of parts during the day. Some big parts and some small parts. We get accustomed to certain nomenclature of these parts. A circuit breaker usually looks like a circuit breaker. A latch usually looks like a latch. A fastener usually looks like something that will hold two or more things together.

Circuit Breaker

There are times, however, when the manual calls out for us to change a part and that part looks nothing like what it really (at least in your own opinion) look like. Perhaps the most widely known example of this trickery I can think of is the "Black Box". We all know that the black box is actually orange, but imagine how confusing this would be to a person outside of the aviation field.

The orange "Black Box"

Often when I change any part of the avionics on our planes I bring the box up to the jetway to do the paperwork. Most of the avionics boxes are black and so when the passengers amble down the jetway to board I usually get one or two remarks about why I'm changing the "Black Box". I even hear parents telling their kids in hushed tones how "that part records all the airplane info". I usually don't correct the passengers unless they address me directly.

This nomenclature issue came up the other day at work. I had a call about the fire warning system not testing properly. When I got up to the plane the captain says that the fire warning system does not test when it's on the DC bus.

This is the first call of my day so after I clear the fog from my brain and take the plane off the ground power bus (onto the DC bus) sure enough the "Master Caution" light did not illuminate when I did the fire warning test. Naturally I'm thinking why would the fire warning test not turn on the Master Caution? Lets BITE check the fire warning box (no help), maybe change the fire control module to see if that helps.

At this point I make myself slow down because changing that fire control box is a big deal. The check out (test) for that control box is about an hour long. Before I do that I call for a wiring diagram for the fire warning DC system. When the wiring diagram comes I start to think I'm going down the wrong route with the problem. Sure enough after some more checks I realized we had a Master Caution problem not a fire warning problem. After I get some more prints for the correct system we narrow the problem down to the Master Caution Dimming Module. Now here is where the real problem starts.

A "Module" to a Line Mechanic is a box that contains wires/lights/relays and all the other little magic electrons that make an airplane do what it is supposed to. A "Module" is a squareish metal thingy that has a cannon plug connected to it.

The wiring diagram says the Master Caution Dimming Relay lives behind the P6-3 panel. Now me and another two guys, lets call them MoneyMaker and DaDude, take turns looking for this module. behind this panel are lots of wires, relays, modules and miles of wires. Each is labelled with a small white sticker that announces its equipment list number. We spent the better part of an hour looking for this module to no avail.

Back behind the panel is also a little door which when opened is hiding a circuit card. All three of us opened that door and saw this circuit card and all three of us were like "well, that's not a module, it's a card".

Long story short one of the guys in the shop must have called Boeing or The Answer Man or someone because a little past an hour later DaDude comes back to the plane and says "So and so says it looks like a circuit card". MoneyMaker and I look at each other and say "No F-ing way!!".

That "module" is a circuit card hidden behind a small door. And to make matters worse the thing is correctly marked, but to see the marking you have to stick your head into the P6-3 panel crane it around and then and only then would you see the Module Number sticker.

So any of you engineers out there:
Why not call that "module" a "card"?
Why not give that little door it's own panel number?
Why not put a little sticker on the damn little door that says "hey, the M(###) lives in here!

Turns out we didn't have the circuit board in stock anyway and once it came in it did fix the problem but the real issue here is the word "module".

Now that I have expanded my work vocabulary to make sure a circuit board can be called a module and likely vice-versa, I'm not really looking forward to the so called 737-MAX and all it's new vocabulary!


  1. Yeah, that and one other 'module' (Mach Warning I think?) are technically in the P6-3, but you can access them more easily from behind the fold-down observer's seat below the data loader panel. I have to pull them every couple weeks to get at the MPN/serial for Wifi susceptibility reports.

    Really, the only thing I want to see on the MAX is something done about the forward end of the tunnel (above the J46/J24 boxes). Squeezing in there behind the gear, or scooting on your back above the E1-4 breakout rack to run a wire that SOME engineer decided absolutely had to run through the nose compartment on its way from the E4-1 to the E2-2 is no fun.

  2. "Wifi susceptibility reports"!! What has become of our profession?

    That MAX will solve some issues we have with the -700 and will create some unique problems of it's own (Engineers be-damned).

    Thanks for the comment Ctishman

  3. Thanks for running this blog. I'm pretty new to the industry, but it's cool to get the perspective of somebody who's been doing it for a while.

    Y'know that "No Wifi while airplane is being used for flight" placard that goes up next to the yaw damper indicator? Someone (and it's usually the apprentice) has to make a day of going through and taking inventory of all the components in the E&E bays/cockpit etc. to make sure the installed parts aren't gonna screw up when someone turns on their EFB. If the part's not on the approved list, it gets routed to stores and replaced, or we get a TSR issued once they check with the manufacturer (this usually happens with the scimitar -800s, which tend to actually have newer components than are on the list). Just one of those little processes that, for all its tedium, makes me glad I chose a career in an industry as thorough about its paperwork as this one is.

    Most of all, I'm eager to see the last of the -300/500s go. They're fucking tanks, sure, but even tanks get replaced by newer, better ones eventually, and the NGs are just so much better in so many ways. Perhaps the MAXes will be better yet, but we won't know 'til the first ones swing by, and even then it'll take a few of them to see what they improved and what they left alone.

  4. This is exactly the perfect example where the new maintenance mobile app AviaTIC would help. This app is a new tool that allows aviation mechanics to create a real life illustrated set of instructions to perform any given task. The app will let you take any number of pictures showing how this "Module" or "Card" looks like and where exactly can you find it. Once you create the TIC file, it will be saved on a cloud server where it can later be accessed at any given time by any registered user. So if a new mechanic ever needs to find that same "Module" six months later, he or she can search for the TIC file by part number and he or she will not have to spend the same amount of time deciphering the manual as you did. You can learn more about this ingenious application at I hope this will help you all in future troubleshooting and or maintenance jobs.