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A GUESSING GAME?

The old analog cockpit instruments did not change much over the years. They had vacuum applied to the system and a spinning gyro that moved the dials to indicate the flight attitude of the aircraft. Today, we turn on a switch and several computers start to hum, and a picture appears on one of the five flat screens in the instrument panel. The advances in technology over the last 40 years are impressive - and come with their own set of challenges.

Steve Watkins   |   1st August 2013
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Steve Watkins Steve Watkins

Steve Watkins is Technical Services Manager, Western Region for Jet Support Services, Inc....
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Avionics maintenance questions come with few answers

The old analog cockpit instruments did not change much over the years. They had vacuum applied to the system and a spinning gyro that moved the dials to indicate the flight attitude of the aircraft. Today, we turn on a switch and several computers start to hum, and a picture appears on one of the five flat screens in the instrument panel. The advances in technology over the last 40 years are impressive - and come with their own set of challenges.

I used to send the old flight instruments out for repair when they failed, and even back in the dark ages of aviation shops had loaner or exchange units for you while your unit was being repaired.

The repair invoices would come to me with similar charges. If the unit was worn out or had suffered a catastrophic failure, the invoice would read “Beyond Economic Repair” with a dollar sign and a few numbers next to it. Alternatively, I would get a list of parts that needed to be replaced for each repair or overhaul - parts like bearings and races, which allowed the gyro to spin at a high speed.

The need for replacement of these parts was determined not only by an inspection at the time of teardown, but by taking into account the 40-year history of repairing these same types of units. This historical track record would help determine which parts wear out, then, after replacing those parts, result in a repaired/overhauled unit with some useful life expectancies. This seemed to work very well, as I seldom had a flight instrument fail again after I replaced the worn out parts.

Maintaining the next generation of avionics was a different story. I would get invoices on units that told me the unit had been inspected, a few diodes and transistors replaced, the unit tested, put into an oven and tested it again, then sprayed with a coolant and tested again. All functional checks would come back good. I would take this unit back to my hangar, take it out of the box, put it in the airplane, turn it on and nothing worked. The unit had failed, out of the box.

Returning the unit back to the avionics shop with a few choice words about the shop’s repair, they would put the unit on the bench, perform the appropriate functional checks, but would be unable to duplicate the problem - and I would land up with another invoice for a second inspection, and, no doubt, for those few choice words.

 

Fast-forward to present day
Moving forward several decades in aviation, the required replacement items for bearings and similar parts no longer appear on invoices for flight instruments. What you have now is a flight panel full of “Could Not Duplicate” or “Failed Out of the Box” units just waiting to cost you plenty of maintenance time and money.

Avionics manufacturers are constantly refining their products with new bells and whistles, and improving reliability rates - and I must say they do a commendable job. After years of experience as a technician and many hours of thought on the subject, I believe I have finally come to a conclusion about why cockpit avionics systems are so hard to maintain…

There are so many questions to ponder when analyzing avionics repair. How long does a capacitor work before it starts to fail? Can you visually see that a capacitor is getting old and tired? After a capacitor heats up for a couple of hours, does it actually start to cause a voltage change to a system that doesn’t like voltage changes? Or will a solder joint, that has started to fail due to the heat and cold causing the joint to grow and shrink on a circuit board, affect the avionics rack 15 feet from the unit that is giving you a problem?

You can take all of the little electrical components that are in computers and cockpit instruments today and apply similar types of questions.

The more poignant questions involving these systems include: How does age/temperature changes/pressure changes/low power/power spikes/quality of material and manufacturing, affect each component? There are avionics manufacturer personnel, sitting in their cubicles, asking these same questions, every day. They may not get an ear-full of choice words from people like me like the old avionics technicians sitting at bench used to get, but I am sure their managers are asking these same questions and searching for better solutions.

The bottom line is, when avionics engineers are asked about how long these little electrical components will last, what affects their failure rate, and at what specific time or interval should we change-out these components. The only answer I can find is, no one knows.

So how do we plan for, or prevent unscheduled avionics maintenance? Maintenance Programs that cover the aircraft’s avionics - like JSSI and some OEMs offer - is one option. Planning to replace the avionics at some specific interval is another.

The first option will protect you from the unexpected costs of component failures and repairs. The second option of replacement comes with the challenge of determining just what that interval should be, because no one really knows the answer. Questions like these with few answers makes maintaining avionics systems of today more of a challenge but, speaking for my fellow technicians, we will persevere!


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