Awareness of EWIS criteria is essential to the success of any new digital electronic equipment installation. In some cases equipment installers are not given the knowledge to fully understand that running a length of CAT 5 cable is not accomplished the same way as installing a similar diameter feeder cable. Network digital buses consist of several independent conductors that are strategically shielded and insulated which makes them for the most part, impedance critical. Impedance is an electrical property associated with resistance, inductance, and capacitance; all of which must be in harmony to allow proper data flow.
The dilemma here, if a wire clamp or even a tie wrap is overtightened, the capacitance factor of the cable may be altered and the end result may be less than desirable. There have been situations where impedance critical cables pass through pressure bungs as they enter or exit pressurized compartments. As compartment pressure begins to increase once the aircraft begins to pressurize, the compression forces exerted by the bung on the cable have resulted in distortion of the cable’s electrical properties and subsequent problems that can be challenging to troubleshoot while the aircraft is on the ground.
The use of improper tooling or failure to engage in lock-out/tag-out procedures can be a costly venture. Should wiring providing reference information to a computerized device become shorted to ground or another power source, the end results may require replacement of the device. Even electrostatic discharge (ESD) has been attributed to knocking out electronic circuits. Many avionics manufacturers will refuse to warranty even new components when they show signs of receiving a static discharge.
Software driven systems do provide end users with a great deal of capability and often flexibility in how the equipment can be utilized. Maintenance technicians and avionics installers on the other hand may grasp the premises of what the desired features and functions are but then have to contend with the variety of anomalies that are frequently present during installation projects.
Equipment/software manufacturers will often develop a test guide, that is used to validate the equipment installation and software functions, that is producing the desired results at appropriate times. The test guide procedures, in some cases, can be used as the return to service reference after equipment repair or replacement to ensure proper operation. This ability should be discussed and validated with the equipment manufacturer as well as the agency certifying the installation.
When discrepancies are noted, the fault diagnosis is often turned over to the equipment manufacturer. This can be done through an on-site representative or by enabling a remotely located specialist to access the system on the aircraft via the internet.
Educating technicians along with interface engineers is a cost that is almost always justifiable. Understanding equipment design philosophy and physical limitations is an excellent first step prior to integrating newer generation equipment to a legacy aircraft.
Locating an electronic box in an area where there is inadequate ventilation or exposure to excessively cold temperatures may result in device failure after a period of perceived normal operation. Once again, problems such as this can be difficult to assess while on the ground.
Probably the most common dilemma with newer technology equipment is the user interface. Unfortunately this takes on several faces. It can be something as simple as altering the power up or shutdown process. The lack of understanding that processor driven devices require an initiation period while turning on as well as a data or setting save interval while powering down. Those that have tried to hurry this process often find it ends badly.
Really, to experience success with the electronic systems of today, knowledge and understanding are paramount. This philosophy holds all the way from the design engineer understanding the aircraft and proposed new equipment, to the installer having knowledge of EWIS along with the specific aircraft standard practices, to the crew responsible for equipment operation, and finally the end users who need an awareness of both capabilities and limitations.
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. You can reach him at firstname.lastname@example.org.