Tuesday, April 20, 2010

Deliberate Eggs

My new hasty packing method is proving to be a pain. Under the old regime I put all the hardly used stuff on the bottom and then the daily used stuff on top, and spent time arranging it all just so. Now everything is just in any order and I hate it. That experiment in speed packing is not one I will be repeating. I somehow find clothes to wear anyway.

At the breakfast I realize that unless I count the stuff on the bottom of the yogurt, the spread includes no fruit. They have little packets of oatmeal, but it's not just oatmeal, it's mixed with sugar and salt. Why do they do that? Everyone who has a stove or microwave available has to them has access to sugar and salt to flavour their meals to taste. Rant rant rant.

This time I'm wearing my toque and gloves. And it's -7. I get out a screwdriver and remove a panel from the nose of the aircraft, in order to get at the circuit breaker inside. The heater circuit breaker is hidden where even the most desperately cold pilots can't reach it in flight, in order to prevent us from blowing up the airplane in an attempt to stay warm, should the heater be malfunctioning. All I have to do is press in that little red button. Ahh, potential warmth.

The fuel crew includes the dog this time but not the daughter. As I approach the airplane I think "aargh." There is frost on the wings and I didn't use the new wing covers. Fortunately it is really sunny and the frost is melting and sublimating. The leading edges of wings are already dry and the rest is fairly soft. I whisk off most of the frost while he fuels and the dog explores the frozen puddle, seemingly fascinated by water that breaks instead of splashes when you jump on it. It's a puppy, only six months old, so it's skinnier and jumpier than it will be when it's full grown. The fueller puts the hose away and I consider saying "don't forget to check the litres," but I don't. We go inside and he realizes that he didn't note the number of litres I took. Ah bad CRM on my part. I should have spoken up. Or even better, I could have noted it out loud, reminding him without letting on that I was doing so. (I glanced at it and saw that it was more than 500 litres, as I expected, but didn't note the exact amount). He goes back out and gets the number.

The building smells vaguely of backed up toilets, and I do say this out loud. It's the water. There's a sign in the washroom advising us not to drink the well water, and whatever is in it that we shouldn't drink builds up in the hot water heater, making the place smell when the floors are washed. Charming.

The remaining frost is almost gone as I start and the winds are calm so I run up facing the other way, making them completely dry before I taxi out to backtrack the long runway.

It's a short flight with beautiful weather. I left my sweater on and never even needed the cockpit heater. What a difference a day makes. The area that was so gloomy and inaccessible yesterday is clear and dry and we encounter no problems. I land on the long runway. It's not butter soft so I say "we're here!" with an implied, "I guess you couldn't miss that," acknowledging that the landing could have been better. This airplane is easy to land well, so I should do it well every time.

After I park I put the wing covers on. The client helps, which is wonderful, but I feel guilty that he's doing my job and I can't really help him do his. I let him know he's welcome to wait in the warm terminal, but he's happy. Maybe he's curious about these new wing covers, too. I'm putting them on partly in case the frost is harder tomorrow, but mostly because it's sunny and there's no wind: a good condition under which to learn to put them on. They are really skookum, with holes for the static wick to go through and fitted tip covers and straps to cover the whole wing outboard of the nacelles. And they're really easy to put on when there's two people in no wind and broad daylight. We'll see later about being alone in the cold windy darkness.

I take a walk through town. As I walk down Fourth Street, the houses on the right side of the street look dilapidated. It's not poverty or a lack of care, but the winter. The houses have spent the last five months being iceblasted by furious winds. The doors lack paint, faux stone facings are worn down to their backing, the edges of roofs are all bashed back. Even brick and concrete looks fatigued. The flat lawns show a little green in the brown. There's no zoning here, so a tanning salon, an upholsterer, a wrecking yard, a church and private homes are all intermingled. My walk ends at the Co-op at 4th and 8th, where I buy hummus and vegetables and a couple of bagels for me. I grin to myself at the old guys in feed caps doing their shopping. It was exactly what I was expecting to see, so it's reassuring to see them. I also pick up a bag of chocolate Easter eggs for the met station people who have been working around the clock so that I have the information I need to stay safe. And it's fun to give people Easter eggs. Now I just have to not eat any.

Even though I had groceries, I decided not to take a taxi home. I didn't tell you which town I was in, not because it's any secret, but because I thought it might be fun for you to figure out where I am from what I've said. I haven't checked to see if there's enough information here to tell exactly where, but you know from the name of the main street what province I'm not in, so go from there. Another hint, which might not help at all, is that it makes me think of Waiting for Godot, but I'm not implying a sense of hopeless waiting for something to happen. Oh and the post title is a little Easter egg for long time readers, because I love you guys for sticking with me all these years.

I eat my dinner and then realize what have I done? Those chocolate Easter eggs are CALLING MY NAME. How will I make it through the night?


wakemp said...

I'd say you have a YEN to fly, if I had to guess.

Jim said...

I almost ended up in Vegreville due to the easter egg, but I'm going with CYEN.

nec Timide said...

I haven't seen skookum used correctly in print for a very long time. Thanks, that little taste of home comes at exactly the right time for me.

Mark said...

That has to be one of the scariest wiring harnesses I've seen. Likely it meets all sorts of regulations, but still looks quite vulnerable to my eyes.

sounddoc said...

because i love detective work like this...

that's a Kelly Aerospace (formerly Janitrol) combustion heater, model B3040...but what i was trying to figure out was the plane that it's attached to :) i'm thinking a small twin or larger single? I'm just starting my commercial rating here in the states, so now i get to study things like combustion heaters, hydraulic accumulators and oxygen systems.

speaking of the B3040, you know the FAA had an airworthiness directive on those back in aught-4? (sadly i know little of the Canadian equivalent of all those types of things...)


A Squared said...

What is it about e harness that you object to?

Mark said...

"What is it about e harness that you object to?"

Not so much object to, but as stated it's scary.

1. Exposed terminals
2. Use of different lugs (I believe I see some spades and rings. Spades should NEVER be used.
3. Tying wiring together with nylon strapping alone. Although I am not certain what is customary here, the concern is vibration which can slowly wear away outer insulation. Best to use a small slip of durable rubber and then tie.
4. Wiring tied together floating in free air. This lends itself to vibrate and flex and eventually will stress the wiring at the lug and cause it to snap. Wiring should be physically bonded to the same device that it is attached to so that vibration is not induced. Using an adjacent terminal block as shown is not sufficient.
5. Tying wiring together without (apparent) consideration of function, and the potential for inductive pickup in closely-strapped wiring.
6. Some of the wiring insulation appears already stressed. The photo seems to indicate some breakdown is either happening or will happen to the insulation due to heat.
7. At least one of the wire markers is coming off. The type used are not sufficient for this purpose. Markers with clear plastic protective coverings or coatings would be better.
8. Doubling of terminal lugs (lower right). This is a total no-no in quality industrial design. It seems unimaginable in a certified aircraft. Doubling puts additional stress upon the terminal block and the terminals themselves due to the flexing involved when screwing them down.
9. I see no evidence of lockwashers or the use of a thread lock. Vibration could eventually loosen these which then could throw sparks. In a potentially fuel-vapor volatile situation, not good.

Conclusion: If I were the inspector of this work I would insist that it be re-wired properly.

Mark said...

.. and I missed three more:

10. The exit of the wiring of the two terminals, upper right, is at a much too strong bend radius. I imagine these pulling out eventually.

11. I see no evidence of anti-corrosion coating. A simple, long-lasting silicone spray would do.

12. Two wires appear to have the same harness number ("2"). Confusing? And hopefully the numbering is reflected somewhere in a schematic.

The only good thing I can find is that two wires aren't stuffed into a single lug.

Is there not protocol for soldering after crimping? If this were my job, I'd definitely consider it.

Aviatrix said...

I can't really comment on the cited inadequacies of the janitrol. It's interesting how many objections you have to it. It looks to me as such things usually look. I can't remember ever seeing aircraft electrical parts soldered.

Perhaps the installation is more temporary than you realize. The whole canister is regularly pulled out, inspected, and sent away for overhaul. I once had a week long vacation in Santa Barbara, courtesy of a FedEx forklift that destroyed our heater on the way back from overhaul.

Mark, I will have a special bonus post for you tomorrow.

Aviatrix said...

I already have a post for tomorrow, Mark's bonus post will be for the day after tomorrow.

Mark said...

A squared.. interesting.

I am no A and P mechanic, I do work in engineering and have developed over the years an appreciation for the finer points.

As Aviatrix mentions that the unit is regularly pulled and serviced, I am surprised to not see a quick-release molex-type in-line connector (with appropriate strain relief and environmental shroud) which would better facilitate removal/replacement. It would be time consuming, mistake-prone, and just plain ugly to remove and replace all those lugs.

Regarding exposed terminals, the comfort level would increase dependent upon the amount of potential exposure. A circuit breaker panel is likely well-entrenched with the back side perhaps not easily or routinely reached?

You note several things as "common practice" but do not address the concern. Particularly in point 4. I would stand by what I noted about that.

Item 5 does make some assumptions and these were predicated upon what I observed in the photo overall. For one, my comments did not point out that the wire jacket colours are the same. This lends amplification to the perception that this is a haphazard mess, not a safe and well documented life-safety device. So I just went a few steps further as clearly each wire has a different role, and they are not colour-coded, then perhaps there's no concern either for EMI.

For item 7, adding temporary markers opens a much greater potential for re-installation error. Some errors will be quite blatant in test (smoke and/or circuit breaker activation; non-function), and others, thanks to Murphy, only become apparent in the air, and in combination with other issues either related or created by the error.

The fact that this mess is regularly serviced (removed?) increases the risk substantially. I am certain there's a nomograph where the risk from non-service versus the risk from service have long-ago intersected in this case. And if it's typical of aircraft (hopefully limited to this type)?


Mark said...

Point 8: back to back is one way to reduce the bend. Still, I would wonder if studs here are of sufficient length to accommodate the extra thickness. The tendency by a mechanic may also be to further-tighten (there are two lugs here so twice the torque) which then stresses the threads, increasing the opportunity of future issues.

Item 11: Corrosion occurs not only on the surface of a material of single constituency (by an outside agent such as salt air) but by the contact of dissimilar metals and/or metals with contaminants. Proper selection of all materials (meeting a spec), preparation of the surface, bonding, and the addition of a corrosion protection block would be good things to do. I see absolutely zero evidence here that any of these are considered.

Item 12: But are they also connected to the same terminal at the other end?

I can understand that soldered connections are discouraged as many folks don't know how to do it properly. I might reconsider my thought on this as soldering of stranded wire (hopefully what has been used here, but who knows) will produce a rather dramatic interface between flexing wire and non-flexing wire strands. Perhaps similar to the crimping in affect, and perhaps demanding as much concern with bend radius.

I observed something else:

13: the terminal lugs have different pedigree and a few have rather short insulation jackets over the crimp terminal portion. When a mechanic wishes to remove the terminal, will they then grab the wire and pull, or manipulate it by the insulation jacket?

The old saying "If it's not broken, don't fix it", may hold true, but likely in the aviation business, the process of manipulating for inspection a mess like this one has in my view the potential to induce problems that otherwise would not occur.

An experienced A-P person can now tell me I'm full of it, and that's fine. But I still wouldn't feel comfortable with that airplane. If this is standard, I should then reconsider flying. Hopefully it's not standard in the commercial world.

Critical Alpha said...

A number of points: tinned copper wire is the standard for use on boats...a corrosive environment.
Mark if you'd seen some of the messes I've seen you'd be calmer about this.
Anyhow it probably doesn't need the heater to fly, though Avi would like it.
As for:
"Hopefully it's not standard in the commercial world."
Maybe not but some wiring harnesses in a B747 do travel inside the fuel tanks rather than outside of them.
You only live once and the only way out of this life is to die.

Mark said...

"You only live once and the only way out of this life is to die."

Straight on!

Aviatrix: a very interesting posting, and perhaps more than you ever expected?

I intend to use this photo with a candidate interview at my company today. We will see what another engineer with considerable experience finds...

Yellowbird said...

"The fuel crew includes the dog this time but not the daughter."

I spent a good amount of time pondering this sentence, wondering if it was some sort of northern figure of speech.

Bob: We stopped at C### for fuel yesterday, eh.

Doug: Did you get the dog and the daughter, eh?

Bob: No, just the dog, eh.

Then I read your previous post. I get it now.

Aluwings said...

I think this manual used to be available online but I can't find it now. Here's a source for the paper version.

It spells out the basics of acceptable practices for certified aircraft.

Ironically, most technological advances in aviation today are made with "amateur-built" aircraft, where there is a much wider latitude to use non-certified materials and methods if a good case can be made that these provide an equivalent safety margin.

Aluwings said...

Wait! On second glance I see this link I posted is for an ebook version - not paper at all. Excellent. Another reason why I "neeeeeed" a new iPad ;-) ... heh heh...

Sarah said...

Wait, Aluwings! If it's a free digital copy of 43.13 1B/2B you want, your wish is granted,

kbq said...

More fun info on wiring (a *large* collection of links): http://www.iasa.com.au/folders/Safety_Issues/Aircraft_Wire/index.htm


Mark said...

I perused KBQ's wiring page (thank you!) and encountered this little gem:

An operator of a Jetstream 4100 aeroplane suffered a total electrical failure just as the aircraft landed.

Investigations were unable to determine all of the mechanisms for the total failure, however, it was established that a chafe of the exciter wire to the positive terminal of the starter-generator was a significant contributory factor to the incident.

The current routing of the small wiring at the starter-generator terminal block has the potential for incorrect routing and possible chafing damage. As the starter-generator is removed for overhaul at 600-hour intervals the potential exists for damage and/or mis-routing of wires during removal and re-installation. This AD requires the modification of the aircraft wiring to reduce the likelihood of total electrical failure.

Very interesting...

Sarah said...

Indeed, Mark. That must have been some "landing" for all the power to go off! :o

Sounds like my landings. Speaking of which, off I go to log some night time.

kbq said...

And if the wiring isn't enough to leave your cortisol levels elevated, everybody can panic 'bout this:


Verification word: skookum


Aviatrix said...

Wow, I posted the circuit breaker picture thinking it might come in handy for some future cold pilot, seeing as initial training on the heater can consist of dire warnings not to let it overheat and a handwave towards the nose. I didn't dream that it would become the main topic of the comments.

I have accordingly added the "electrical" category to the post, and resolve to post more photos of airplane innards.

A Squared said...

I must say that I have been singularly unimpressed by Molex connectors, so offering them as a "better way" doesn't strengthen your position much. Taking the broader context of using a multi-circuit connector in general....OK. That particular appliance may be found in perhaps a dozen or more aircraft models, from at least 3 different manufacturers. It may be removed from a 1966 Cessna 320 and exchanged for a freshly overhauled one which last was installed in a 1974 piper Navajo, after overhaul it might be installed in a 1996 Beech Baron. I'd be interested to hear your scheme for ensuring that it will be "plug and play" over half a century or so of aircraft manufacturing.

You seem to be suggesting that the heater be left in place rather then serviced periodically. while I understand that at some point, too much wrenching can create more problems than it fixes. I would suggest that this is not one of those examples. The combustion heater has a limited life span. Given enough time in service the combustion liner *will* burn through, at which time it fills the cabin with carbon monoxide and kills everyone or it creates a nice little fire in the nose of the airplane which spreads back and kills everyone. I expect the first is a more peaceful way to die, but you don't really get to choose. Might be better to pull it out every once in a while and test the combustion chamber, even if it does result in the harness having to be rewired occasionally.

Aviatrix said...

I don't know if it's relevant in this case, but a lot of aircraft parts are deliberately less robust than their automotive or industrial equivalents because they have to be light enough to fly. We replace resistance to abuse and wear with pilot training and frequent inspections.

Many cars are used daily and have the hood opened once in six months for an oil change. My airplane gets an oil change every fifty hours that it flies--i.e. every four days when conditions are right--and half the airplane is internally inspected at every oil change.

Mark said...

Aviatrix, it would be interesting (and perhaps the language entertaining) to hear a response from your A&P mechanic to this thread.

Anonymous said...

On the subject of crimp -vs- Solder.

Over the years I have serviced a variety of equipment that was subject to vibration, and have found that terminals that have been crimped and then soldered fail much more readily than a terminal that has been (correctly) crimped alone. The failure point always seems to be in the area where the solder that has wicked up the wire ends. It seems to either make the wire more brittle, or prevent the stress of flexing being transferred over a wider radius?

My 10 cents worth anyway.

Verification word "ousto"
Telling someone to get out with much gusto. :)

GA with L Plates

zb said...

I completely agree to Anonymous' comment on solder over crimped contacts. Even worse would be first soldering a tinned wire and then crimping it. Crimped contacts (without solder) are very durable when it comes to vibration and mechanical shock. Far better than anything that's soldered.

Mark said...

ZB, I am leaning towards that myself.

One person writes, "If you can crimp, crimp. If you can solder, solder. But just don't do both." (http://www.ch601.org/resources/crimpsolder.htm) The premise being that a good crimp connection is just as solid.

Here's a site http://www.groundfusion.com/faq.php that suggests soldering a crimped connection will be problematic: "When solder is present in a crimp, the deformation properties change. When the deformation properties change, metal-flow, cleaning, welding and residual force also change and compromise the mechanical and electrical properties of the crimp. With diminished mechanical properties, the connection may not survive normal uses. Furthermore, as electrical performance diminishes, the perils of static heating arise. Additionally, in some cases, copper wire may become embrittled or solder wicking may affect the flexure strength of the stranded wire. By soldering a crimped connection, the process heat may compromise the crimp."

I'll take this lesson into my work as I have leaned on soldering my crimp terminals for "extra safety".

Hoping Aviatrix' A&P folks are using crimp terminals with appropriate tooling for the specific terminal. This match-up tends to be expensive (versus a general purpose tool via a radio shack or other store) but it assures that the engineering is solid and the performance may be relied upon.

Anonymous said...

Sadly, Mark does not know what he is talking about. Every sentence he writes screams out that he does not know what he is looking at, or where or how it is installed or used or maintained.

A Squared's remarks concerning Mark's complaints were very charitable.

If I were the inspector for Mark's comment, I would insist on rework.

Likewise he should rework his comment where he states that Aviatrix's exercise regimen will be useful since it will help her push-start in the event of a stall.


In all seriousness, though, when those without aviation backgrounds get into the aviation world and make aviation decisions, Bad Things Happen.


Footnote: I know exactly what that is and what it's installed on. A cursory review of the archives suggests that Aviatrix has never stated her airframe. As this is probably intentional, I ask readers who are in the industry to respect her wishes.

Mark said...

I don't think Aviatrix meant this to be a pissing contest.

"Sadly, Mark does not know what he is talking about. Every sentence he writes screams out that he does not know what he is looking at, or where or how it is installed or used or maintained."

Please substantiate. Why is it sad? I am here to learn.

"If I were the inspector for Mark's comment, I would insist on rework."

How so? Please substantiate.

"Likewise he should rework his comment where he states that Aviatrix's exercise regimen will be useful since it will help her push-start in the event of a stall."

I cannot find this remark in these comments, although it does sound a bit like my sense of humour. Note the humour part.

"In all seriousness, though, when those without aviation backgrounds get into the aviation world and make aviation decisions, Bad Things Happen."

I do have an aviation background. Fortunately I am not making the decisions, otherwise the A&P mechanic on this job would, in my view, be out of one.

But if you substantiate and instruct, we may all learn together.

Aviatrix said...

My PRM said he had high confidence in the AME who laughed at Mark's list, and I'm glad, Anonymous, that you have the knowledge to independently confirm that the heater installation is not a deathtrap, but seeing as you have more time to comment on such things than my AME, I (and it sounds like Mark also) would be interested in seeing a point-by-point refutation of the issues Mark listed.

I don't know one way or the other. I compare things to what I have seen before, especially what I have seen approved by maintenance folk I trust. When I look at wiring I only have cause to complain if it has obvious mechanical deficiencies, such as being loose, frayed, pinched, rubbing, charred or stretched.

Anonymous said...

Well, since you ask nicely, and have an open, inquisitive mind - I am willing to devote some time to this. But you will have some work to do too! I will not have lazy students!

Here's my general plan: Theory, Practice, and selected topics. More specific syllabus TBD.

For the Practical/Lab portion of this proposed online mini-seminar, can you go to an aerodrome/airport, and look at a few combustion heater installations? Are you ready to jump into the deep end of the pool?

Say Yes, and we will begin tomorrow!

Aviatrix said...

Anonymous (could you do us the favour of registering a name?): Viewing an aircraft heater installation requires removal of external panels, and I have already shown you the heaters on all the airplanes I have access to at the moment, but I imagine there are readers who could contribute additional pictures, so yes, of course.

I may be able to find some photos of the canister removed from the aircraft, or of the same combustion heater installed in another member of our fleet.

Aviatrix said...

All I could find was an earlier pic of the same heater, but a wider view because I was photographing the heater, not the button on that occasion. That will go up tonight.

Please e-mail me the explanation (there's a pretty low limit on comment length) and then I can put it up. where people will see it. Mark, if you want to add more details on why the issues you mention are relevant in the non-aviation environment, you're welcome, too.

Mark said...

Aviatrix, I am ready to know why the concerns I raised are not relevant to the aviation environment. Going over the list I believe they fall into these categories: vibration tolerance, heat tolerance and dissipation, security of physical and electrical connections, corrosion, short/cross-circuit prevention, signal crosstalk/noise induction, color-coding and marking, and general neatness of wire routing. The ability to service components with the least disturbance to connections is something I might add as it's a feature that if done right can lead to increased lifetime of the connecting wires/connectors, manipulated during the service.

All of these areas above provide failure opportunity, particularly in the potentially hostile environment beneath a cowling.

In my ground-based each of the named considerations come into play just as much as they would if it were my air-based world. The difference is that failure on the ground is expensive in time and cash. Failure in flight adds an obvious risk.

In a previous posting in which you discussed handling electrical failure (don't press the circuit breaker in if it popped), I cringed at some of the NTSB reading. Now, seeing the spaghetti wiring photos you presented, it's a wonder to me why in-flight electrical issues are not more frequent. Why the Swissair accident happened was puzzling, until I read somewhere that power to the IFE system was hacked in place and did not have its own over-current device.

Maybe electrical failures are frequent.. just not catastrophic enough to come to the surface in the reporting?

Aviatrix said...

In my experience, yes: electrical failures are common. I couldn't enumerate the times I have seen electrical instruments fail in flight, and I'm probably missing some when I say I have had three smoke-in-cockpit instances attributable to electrical components.

Anonymous said...

Fantastic! This will be fun. We can all learn things from each other.

Session 1, Comment 1

A. Theory
Let's examine some theory. Mark, you're up! Let's go with your "gotcha" list, numbers 1 and 2. Explain the theory behind each one. Develop your points. Something is bad; but why is it bad? If something is bad, then conversely, something else is good, i.e., the standard practice. What is the standard, and what objectives are served by the standard? Explain fully, but stay within the comment word limit.

B. Thought question
This is for everyone: should Aviatrix's aircraft carry a chaff dispenser? Why, or why not? What are the benefits and drawbacks?

C. Practice
For anyone who's seen an aircraft combustion heater in situ. Describe where it was located. Think particularly about the meaning of that location to the heater and the aircraft. Think like a designer.

Aviatrix said...

Anonymous, if you are (a) going to remain anonymous and (b) call bullshit on someone else's carefully worked post, you need to start producing something other than smart remarks in order to be taken seriously. 1 & 2 are the only items on Mark's list that don't already have rationalizations, and even I am fairly confident hypothesizing that the risk of exposed terminals is having a metallic object bridge them, and the risk of spades as opposed to rings is that they do not totally surround the retaining screw, thus depend on friction not to slip out.

You and everyone else know perfectly well that there is no reason for a chaff dispenser on this aircraft, and the heaters are located in the fuselage, because that's what they have to heat, but not in the cabin, so people can't futz with them or burn themselves on them. They're not in the radome because that's where the radar is, which pretty much leaves one spot for them in nose and tail.

sounddoc said...

hmm, no need for a chaff dispenser, unless....aviatrix are you really a next generation Stringfellow Hawk, and these jobs, or 'missions,' if you will, are flown in airwolf?

because that would be totally awesome. :)

Anonymous said...

Session 1, Comment 2

Chaff Dispenser: The issue is solving problems you do not have. Does it increase safety? In the current environment, perhaps, but no more than an iota. Should it be installed for that iota of safety? No, because safety measures have costs; the benefits do not outweigh the costs. Safety measures carry their own risks, as well.

Item 1: Exposed terminals. It is important not to miss the aircraft for the wires. The designers' objective was safety of the airframe and safety of the passengers. The combustion heater is located in a sterile, limited access, protected area. There is nothing to fall across terminals. Passengers cannot access it. Baggage is not stored there. There is circuit breaker protection. Covering the terminals is solving a problem you don't have. (Though you could; the cost would be small. So would the benefit. And so would the risk.) Non-critical system, sterile area, protected area, circuit breaker; a double layer of protection, or more if you include other things. The designers achieve their goal of safety of the airframe. They do it in a way that some of us are unused to seeing.

Item 2: The much-maligned, dangerous spade terminal! When's the last time you plugged in a toaster .... The terminals are all rings, anyway.

Flat Spin said...

Session 2, Comment 1

Let's examine points 8 and 10. Interesting - Mark, what are your references for 8 and 10? When you look at the photo, what gauge wires do you see?

Supplemental reading for the ambitious: AC43.13, located by Sarah, above.

Mark said...

It may be argued that spending a little more (50 cents for a piece of guard plastic - commonly provided with exposed terminal blocks) is a very reasonable thing to do.

Each accident/incident seems to teach designers, engineers, manufacturers, and servicers something new that they had not considered prior - or perhaps thought was unnecessary.

The sky is an unforgiving teacher.

flat spin said...

Session 2, Comment 2

Mark - still no reference?

If you're not going to participate, I'll cut to the punchline and be on my way.

To conclude session 2, items 8 and 10 are addressed by AC 43.13, chapter 11.

Now the punchline:

Why did the mechanic laugh, specifically laugh?

Because that's how heaters come from the manufacturer.


Final PSA

The wiring in that picture isn't scary; however, all too frequently, there is scary wiring on aircraft.

Safe travels.

A Squared said...

If you're not going to participate, I'll cut to the punchline and be on my way.

It became apparent early on that Mark wasnt interested in actually reading and responding to anyone with actual expereince. That's why I quit responding. Limited enthusiasm for being having him once agian reiterate his initial observations without addressing anyting which was posted, I suppose.

Mark said...

I made a statement about doubling up terminals on a block saying that it was good industry practice to avoid it. Yet I can't locate any reference that would back it up.

In our shop, the practice is avoided.

But I note that the Advisory Circular (thanks for pointing to this) covers this by stating "no more than four" to a lug.

There does not appear to be any spec for torque (they just say "tight" for inspection requirements).

Meanwhile, there's a lot of reading to do.

Note that the questions and comments come from the perspective of an A&P outsider. However, I still can't help but wonder how wiring as illustrated is allowed to fly.

Mark said...

"It became apparent early on that Mark wasnt interested in actually reading and responding to anyone with actual expereince."

I don't appreciate the inference.

There is such a thing as not having a lot of time.

I am very interested and, as stated, wish to learn.

It would be helpful if participation did not include personal attack.