Avionics Technology: Things I Have Learned

Hazards abound in our industry, in fact it is common when I encounter an old friend and say hello from a ways off, the most frequent response is “what did you say?” Who would ever think that aircraft mechanics could be hard of hearing? Most of the tasks we undertake involve an element of risk, be it radiation while troubleshooting a radar system or electrical shock from a stray wire or even static discharge from an improperly bonded panel.

Many of the chemicals we come in contact with on a daily basis contain warnings that would cause most logical people to question why they were ever produced, yet with proper knowledge and protection they are used with the desired effects. Situational awareness is a key element to survival in our trade and in an uncoordinated shop co-workers often contribute to personal injury.

Wiring/electrical anomalies
Electrical Wiring Interconnection Systems (EWIS) is a relatively new concept and was proclaimed in Advisory Circular 25.1701-1 published at the end of 2007. This was the start of enlightening technicians about the anomalies that may arise when wiring for various systems is collocated in bundles and wires are found in various shapes and sizes for a variety of reasons and one size does not fit all applications. Who would ever think that locating a video cable next to an antenna coax could result in degraded radio communication? Along that same line, there may be a reason why the installer that fitted the communication radio coax left that extra cable coiled up and secured. With certain systems the transmission of radio frequencies (RF) is enhanced when the transmission line (coax cable) is cut at a specific dimension to coincide with the wavelength of the RF used. A second bit of insight with coax cables is that they can be sensitive to clamping techniques. An overtightened clamp or wire tie can compress the coax altering the impedance which contributes to signal loss.

Experience is another excellent teacher when it comes to the use of sealers in and around electrical connectors. Some products do contain materials that are conductive even though they do not appear to create a short to ground it may impact the performance of digital buses or other impedance critical circuits.

Just because it worked that way before . . .
A few other noteworthy revelations include: just because it works that way in one aircraft does not always mean that if another aircraft does not perform in a similar fashion that a problem exists; assuming any polarized capacitor you encounter is fully charged; the shielding on a wire is always intact; the electrical connection or switch is good because the ohm meter displayed low resistance; discourage the suggestion of a coworker that you go check for power at various points while they look at the wiring diagram and advise you; and when an engineer uses the term “impossible” consider that your judgment is probably on the right track. Probably my most perceptive conclusion is that “Murphy” must have been an aircraft mechanic.

While perusing the box full of old training certificates, I undertook the mission of totaling the hours that I spent in a learning environment in the last 30+ years and came up with the fact that I have accumulated the equivalent of 11 years worth of course hours. The last lesson I learned is when my Dianne reads this she will figure she was bamboozled regarding my participation in this year’s house cleaning and I will have to come up with another idea for next year to get out of the annual household purging of junk.

Jim Sparks has been in aviation for 30 years and is a licensed A&P. His career began in general aviation as a mechanic, electrician, and avionics technician. In addition to extensive hands on, Jim created and delivered educational programs for several training organizations and served as a technical representative for a manufacturer of business jets. Currently when not writing for AMT, he is the manager of aviation maintenance for a private company with a fleet including light single engine aircraft, helicopters, and several types of business jets.