Getting Old

The toll on aircraft and avionics systems


The effects of aging on the human body often include degradation of the senses, aches and pains, restricted range of movement of limbs, the loss of control of various bodily functions, and of course the dreaded smell of old people. I still hear my mother telling me that I had better take care of myself now in order to hold off the onset of aging. In addition to lifestyle, environment can play a big role in longevity.

Many of us in the aviation maintenance field have had personal experiences with aircraft that appear to exhibit almost human-like personalities and, periodically, those that could be possessed. An old friend of mine had been hired on with a Fortune 500 company two weeks before they procured their brand new business jet. During visits to his hangar over the years, I routinely witnessed him talking to the aircraft while plying his trade and for 28 years the aircraft performed admirably. Two years after my friend retired the aircraft was sold as it had become problematic. Sounds like stuff for the twilight zone but most of it can be attributed to the cantankerous nature inherent with growing old. Like humans, the aging process can take its toll on aircraft and avionics systems.

Electrical Wiring Interconnect Systems (EWIS) has generated significant interest in recent years. So much so that Federal Air Regulation 25.1701 was created to ensure a well-defined method for achieving longevity in future aircraft designs, while the current challenge is to ensure safe and reliable operation today.

Most technicians are aware of initiatives sponsored by airworthiness authorities concerning aging aircraft issues. Many are structural in nature, dealing with the effects of fatigue and corrosion. Unfortunately it is often overlooked that the same two conditions can have serious impact on avionics.

Another detriment faced by many is acquisition of an older aircraft either through secondhand purchase or flight department mergers. In some cases, previous maintenance history may be all but unknown. A desirable (but not always practical) approach is to start at the nose and work back through the tail, looking for signs of areas that may require attention.

Radome
A radome is a very good example of a device that tends to mask defects. Unless a significant event such as impact damage occurs, it will remain in service while continuing to degrade. Today many of these protective fairings are fabricated using exotic materials such as quartz or a honeycomb composite, but in years past, fiberglass was the choice of many manufacturers. Transmissivity of the radome is its ability to allow radar energy to pass freely. In fact, current Class A radomes have a transmissivity of around 95 percent. This capability can be reduced by certain types of inappropriate repair or even excessive paint thickness.

Some styles of radome are also prone to erosion which can allow moisture to find its way inside the structure. Water will tend to absorb some of the radar energy. In severe cases may cause a significant reflection, resulting in a radar image constantly showing the aircraft in weather conditions.

Anti-erosion boots may be applied to the nose in an effort to reduce the effects of impact wear and may themselves be a cause of reducing transmissivity or can even cause electrostatic buildup. Electrical bonding is another concern with radomes, as most materials used in their construction tend not to be good conductors of electricity. As a result, specialized paint processes are often used to enhance conductive qualities and thickness of the combined coats have been found to reduce radar sensitivity. Static diverter strips are frequently applied to assist in the dissipation of electrostatic charges back to the airframe.

Condition of static strips, along with the appearance of their bonding point, can provide valuable information regarding their operational abilities.

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