Update from the "new engineer in the field" 1

[koopas]

Hey all,

Whoa! Can't believe it's already been about five months since my original post entitled "New engineer in the field - needs advice". At the time, I was a little lost at my new job. Time does fly by fast.

Just to give you an update, I went ahead and took the FSB part I course but decided to hold off on part II. After two weeks of part I, my brain was COMPLETELY fried. The topics weren't too complicated but everything was new. Hell, I didn't know what a shim was. I even asked the dumb question "what's a stringer?". I knew what a longeron was but I guess that's Douglas terminology. Basically, coming from a guy who didn't know how a rivet was installed, you can feel my plight. So I ended up going back to work after part I to try to apply some of the knowledge I acquired in Seattle. From what I heard, one should be able to handle most repairs that are beyond the SRM with just part I. Part II just goes a little more in depth and is more theoretical. Part III is more practical and hands-on?

Since I work for such a small airline, I've been working on lots of different stuff...some meaningful, others not as rewarding. Unfortunately, I haven't really put the FSB course to use. Most of the few repairs I've handled have been per the SRM (within limits) or simply asking an 8110 from Boeing (and let their service engr. guys figure it out).

Lately, I've doing a lot of stuff on ATA 24, AC generation. I've never been a big fan of EE but getting in depth with IDG's is interesting. Once again, the realities of basic electrical, applied knowledge is not taught in school. When the FIM first said "Check for continuity between pin x and y"...when x is on the IDG and y is in the E/E bay, I was a little startled. How the heck am I going to find two wires long enough to connect to each pin from the multimeter? Needless to say, all the mechanics were on the floor dying laughing. Now for a question...are the following the only methods to do wiring or electrical checks/troubleshooting:

-continuity
-short to ground
-check resistance


Anyway, my slow journey of knowledge continues...I hope I can do more repairs since I feel a little more competent in that area. However, my dept. already has two every experienced structures engineers so they handle most repairs. By the way, are any of you going to either a Boeing (or rather Douglas) Structures/Composites training conference in Long Beach at the end of March? Also, I am planning to attend some Structures conference hosted by Boeing around that time. Of course, I just tried accessing my work email to get the details but it's down...go figure. Anyway, your local Boeing field rep. should have the details.

Keep the encouragements coming I'd appreciate any advice on new books to read, training to take advantage of, and the like. Thanks again for the support.

Newbie Alex

P.S. It seems that people don't discuss specific technical problems or issues pertaining to their jobs on this message board. So, I am also reluctant to ask questions with the specific details that may reveal privileged or confidential company info. What's the rule of thumb here? I am also new to this "corporate" world.

 

[nickbo]

koopas
It is good to see a "new " person willing to show their perspective of what they are going through. Some times those of us of chronological depth, forget what it was like to start out.
As an EE with an A&P license, I agree with your statement about realities of basic electricity, troubleshooting not being taught in school.
I just had a new EE start to work for me and she is in the same spot as you, no toubleshooting knowledge
In electrical troubleshooting there are many more aspects than just continuity, short to ground, and resistance checks
Just to name a few:
Voltage checks
Visual inspections
Using schematics/wiring diagrams
Thinking about the problem and developing an approach
Special test equipment i.e. oscopes, tdr meters, meggers, etc.
And more.
Troubleshooting is an ability that is aquired over time and two people might troubleshoot the same problem in a different manner.
There are many courses out there on electrical troubleshooting techniques.Check the Web.
A suggestion to start:
1.Select a certain system (That is functional)
2.Pour over the wiring diagrams and really learn the system.
3.Make electrical checks to see how a known good system works.
As to troubleshooting a specific problem:
1. Verify the problem
2.Analyze the problem
3. Develop an approach to the problem
Simple example in your field:
Boeing 757 has a tail light that is not working
First level:
1. Verify that the light is out
2. Logical approach, simple and most logical choices first
3.Is the switch turned on? Is the circuit breaker in?
Is the light bulb burned out?
4.All of the above are good
Next level:
1.Start electrical checks Is there voltage at the light bulb? Is the ground the bulb good?
2. If the voltage is not there you now need to systmatically
isolate the problem. As you know on an aircraft there would be many electrical disconnects between the cockpit and the tail light. One method that I like to use is what I call divide and conquer. If there are 8 disconnects I would "divide" the system in half. You do not need to check each one step by step. If you go to disconnect #4 you can eliminate half the system at once
3. Keep dividing the system until you isolate the problem.
I realize that this is a very simple example but that is a good place to start.
Also, don't be afraid to ask opinions and thoughts from your more experienced mechanics.
Sorry to carry on
Good luck
nickbo
P.S. Don't be afraid to ask specific questions. You can do so without compromizing company propritary info. 99.9% of the people are here to help each other.

 

[koopas]

Nickbo,

Thanks for your reply. Here are two questions:

The first one is rather stupid: In your tail light example, to check the voltage at the light bulb, would you just stick the two ends of the voltmeter at each terminal of the light bulb, and expect a potential difference equal to the bulb's voltage rating?

The second one is broader. How would you check a system for intermittent electrical faults?

Thanks.
Alex.

 

[koopas]

Nickbo,

One more thing, do you know of a good book on APPLIED aircraft electrical knowledge and troubleshooting? My EE book from school doesn't help much in that department.

Thanks.
Alex

 

[FredGarvin]

Koopas,
In regards to the book, I'd suggest going to any A&P website and look for book titles. I have read a couple of good books that dealt specifically with aircraft electrical systems that explained quite a bit. The two I read (and can not remember the names of) were entitled exactly along the lines of "Aircraft electrical systems." I too was in your position and had to learn a lot about IDG/CSD's and generators. I had to get more in depth than you probably will because we tore them down and repaired them, but it was good reading nonetheless.

As to your other questions...

1) Yes. Voltmeter to each terminal to measure potential is what you're looking for.

2) The intermittent electrical gremlins are the biggest pains in the butt. It really does help to have experience in these cases because if you can't readily see the problem, you have to be able to take some educated guesses as to where to look. That comes with time. The basic things to always do for an intermittent are: Check for loose wiring. Look for fraid or partially broken wires. Look for chaffing or places where a bare wire can occasionally make contact and ground out. There are a lot of others, but those are the big ones off the top of my head.

If I had 1 suggestion to give to you it would be to become intimately familiar with all of the electrical diagrams. The answers will always be there, you just have to know what to look for. If you find a problem without looking at a schematic, go back and look at the schematic and locate the problem on it anyways. This helped me immensly when it came to learning systems.

Good luck.

 

[nickbo]

koopas
FredGarvin answered your questions very well.
A little further insite:
1. In my tail light example, I was using a 28VDC system. (Sorry about not stating that).
2. As to books in additon to what FredGarvin stated,try a web search "aircraft electrical systems books", you will see many listings
3. Intermittent problems: Once again I agree with FredGarvin
as these are the worst problems to fix.
Example:
Navy aircraft on an aircraft carrier, pilot reported that the landing gear would not retract.
Maintenance put the aircraft on jacks an cycled the landing gear several times, worked great.
This happened several times, in the air the landing gear would not retract, but in the hanger on jacks it worked fine. The pilots were getting upset and the maintenace types frustrated.
Cause of problem:
In one of the electrical connectors on the landing gear system, one of the electrical pins locking mechanism had failed. When the aircraft was launched off the catapult the pin would slide back (no contact) due to G forces. When the aircraft returned to the carrier, the arrested landing applied opposited G forces and the electrical pin re-seated!
How would you like to try and find that one?
Good luck in your endeavors
regards
nickbo

 

[andyUK]

hi koopas

This is a bit outside my field of expertise as im an aircraft fitter but in respect to wiring testing it can sometimes be a good idea to test for voltage drops under load. Let me explain why.

we are currently carrying out 'lightning strike' testing on one of our aircraft. After one of the tests the aircraft power dropped off line for no good reason. after much head scratching the problem was eventually traced to a connector on a generator control unit

when the core had been stripped to allow the pin to be crimped some of the cores had fractured thus reducing the current carrying capacity of the core. During the simulated 'lightning strike' the current spike caused the core to overheat and fracture compleatly.

up to this point the system had peformed without fault. also this manufacturing fault would not have been detected by simple continuity and insulation tests.

If the failiure had occured during a real lightning strike during flight the all a/c power would have been lost from the no 1 system giving rise to serious aircraft safety implications

There is a company in america somwhere called DITMCO (drive in theatre movie company) who specialise in designing and building automated aircraft wiring testing equipment that can test cabling and connectors under system load conditions

hope all this helps a little

its good to see a graduate/office type who is willing to listen to shopfloor types

keep up the good work

 

[JayMaechtlen]

Greetings!
I have to admit at first, I'm not an aircraft type, but:

In terms of general troubleshooting-
Isn't it worthwhile to make a visual inspection, then a manual inspection- are connectors properly seated, do they "feel right", etc?
Are harnesses secured, run properly- is one or a group of wires pulled tight at the connector, leading to various failures?

"one of the electrical pins locking mechanism had failed."
would that have been detected by manually shaking or tugging the connector assembly?

regards
Jay Jay Maechtlen

 

[macdonaldallan]

As a somewhat crusty engineer - who still has a brand new Pickett 800-ES with belt holster, I have used TDR (Time domain Reflectrometry) to find intermittent shorts on large engine harnesses.

This could be done on a carrier as the EW guys usually have something like this.

One word of caution, before using this technique make sure that all electrostatic sensitive devices are disconnected - if not, follow the smoke.

This is a somewhat specialised tool so you may have to ask around to find someone in your area who knows about it. A good link to describe the technique is:

http://www.tscm.com/tdr.html

It's Monday morning and my coffee cup is suffering from dehydration.

 

[jcai]

GOOD MORNING FOLKS - I THINK ALL OF THE ABOVE WILL HELP ANY NEW GUY WHO IS GOING TO TACKLE TROUBLE SHOOTING ON AIRPLANES / HELOS - WHETHER MILITARY OR CIVIL - I STILL FIND MANY OF THE PROBLEMS ARE CORROSION - ESP ON MALE OR FEMALE PINS IN CANNON , ELCON OR REBLING TYPE TYPE CONNECTORS . SCOTCHPAD IS HANDY ITEM IN SNAP-ON TOOL BOX -I ALSO HAVE SEEN THAT PUSHED BACK PIN MANY TIMES AND ALSO THE HAIRCUT ON CABLE STRANDS CAUSING OVERHEAT UNDER LOAD - I LIKE THE MENTION OF TESTING VOLTAGE UNDER LOAD - MANY FOLKS FORGET THAT LOAD BIT ! THE STD FLUKE TYPE MULTIMETER IS STILL A VERY GOOD TOOL IF USED PROPERLY I THINK .
FOR NEW BOYS - THE LARGER TURBINE AIRPLANES / HELOS AND MOST MILITARY ARPLANES / HELOS - RUN 208V/115V. - 400HZ SYSTEMS WITH ALSO 28.5V. D.C. VIA T.R.U.AS WELL + USUALLY AT LEAST ONE SINTERED PLATE VENTED MAIN NI-CAD OR S.L.A.B. TYPE BATTERY . MANY OTHER BACK UP SEALED NI CADS ON BOARD ALSO . COULD ALSO BE S.L.A.B.s ON BOARD IN G.N.S./ I.N.S. / EM. LTS ETC. MANY ARE FREQUENCY / VOLTAGE WILD SYSTEMS - THE NEW A.380 HAS NO SUNSTRAND C.S.D.s
IT ALSO IS 5000 P.S.I. ON SKYDROL - SO WATCH IT IF YOU ARE GOING TO BE WORKING ON IT .
SOME U.S. MILITARY AIRPLANES ARE 270 V. D.C. ONLY WITH S.S. INVERTORS FOR 115V. - 400HZ - THIS IS ALSO USED ON SPACE STATIONS .
TRUST THAT HELPS A LITTLE - J.C.