A Walk Through Repair: How It’s Done: Avionics Repair

By Ernie Stephens | April 1, 2009

Repairing airframes and powerplants is tricky enough. But what does it take to get today’s aviation electronics back online?

Last month, R&W visited an engine shop to see how engine work is performed. But from time to time, problems will arise with an aircraft’s aviation electronics, better known as avionics. Avionics includes voice communication gear, navigation instruments, systems monitors, flight computers, and much more. When it’s time to fix or upgrade a helicopter’s avionics, it’s off to the shop for some specialized attention.

For Helicopter Transportation Services (HTS), major avionics issues are dealt with by HTS Avionics (HTSA), the company’s subsidiary located at its corporate headquarters on Martin State Airport (MTN) in Baltimore, Md. There, General Manager Derrick Sweitzer and his team of certified experts perform surgery on sick avionics under their FAA Part 145 repair certificate for company aircraft and outside organizations. And there is always work to be done!


"We have very good examples of everything," said Sweitzer, a certified avionics repair technician himself. "I have a finished product out here; an S-61 that we worked on for a month-and-a-half to upgrade the avionics to make it Part 135. And then we have a Bell 214, which is a complete rewire project, as well as an avionics upgrade."

HTSA’s complete cycle for avionics component repairs includes: site removal, authorization to ship, work order assignment, bench check, repair and service, function testing and return shipping.

Site Removal

Whether the problem piece of avionics is from one of HTS’s 80-plus helicopters stationed around the globe or a personally owned kit plane sitting on the other side of the airport, step one is often the removal of the offending item. For a panel-mounted unit, such as a radio com panel or a transponder, this is rarely more complicated than backing off on a set of fasteners, sliding the cabinet out of the instrument panel, and disconnecting the cables from it. But other systems with control panels up front where the flight crew can reach them may have most of their electronics in a separate box mounted in an avionics bay elsewhere in the helicopter. Extracting those can also be as simple as unbolting them from a bracket, but some have complicated wiring arrangements that could require hours to disconnect. This is why certified maintenance professionals should be called upon for their removal.

As a repair shop with authorization to work on non-company equipment, HTSA often has private owners and other companies bring their aircraft in to have a component serviced. When this happens, technicians will remove the equipment themselves and simply walk it back to the shop inside of HTS’s huge Baltimore hangar.

Authorization to Ship

Typically, a private owner can ship anything out for service whenever they wish. But for a large company like HTS, the protocol is for an on-site supervisor to coordinate shipment to the shop. The piece of equipment is then carefully packed in a box or crate with plenty of protection all around to survive the trip without damage. The packages contain all of the aircraft’s documentation such as: from which aircraft the unit was removed from; how much service it has seen; and a detailed description of the problem at hand.

Work Order Assignment

Upon its arrival in Baltimore, an HTSA technician will take the equipment, review the paperwork, and assign a work order to the job. Everything is then tagged for easy identification and to ensure that the right piece of equipment is returned to the right sender.

HTSA technicians pay special attention to the manufacturer’s restrictions on the repair of particular pieces of avionics. Multi-Function Displays (MFDs) from glass cockpits are frequently the subject of repair restrictions.

"Nobody is allowed in there," said Sweitzer of the MFDs that he said can cost as much as $20,000 each. "No Joe Schmo can open them up...there’s no manual for opening them up. They have to be sent back to the manufacturer." The technology used to build and repair those, he said, is too complicated and proprietary for the manufacturer to trust in anyone’s hands but their own. So, HTSA, as well as most other avionics shops, serve only as a liaison between the aircraft operator and the makers of MFDs, saving their time and efforts for the repair of today’s more standard electronics.

A priority is assigned to jobs that will remain in-house. It is based upon whether or not the aircraft the item came from is still flying with a back-up unit, or is grounded until the broken equipment can be returned. "High priority items come in and get torn apart right away," said Sweitzer.

Bench Testing

The first rule in repairing or replacing any piece of electronic equipment is for the technician to see for himself or herself what the equipment is doing or not doing. The most efficient way to accomplish this is to take the item into the shop and bench test it.

Bench testing avionics consists of trying to recreate the operating environment of the questionable unit in a controlled, carefully monitored environment that will pinpoint the problem. During our visit to HTSA, R&W was introduced to Bernie Ulbrich, a veteran technician with more than 30 years in the aviation business. He is a licensed airframe and powerplant mechanic and is authorized to conduct inspections. He was working on a Northern Airborne Technology AMS44 multi-user audio control panel that belongs to the company. The complaint from the field was that it wasn’t getting any power.

"I have the schematics for this unit," said Ulbrich, pointing to a large, unfolded electronic diagram of the exact model he had partially disassembled on his workbench. Behind him were shelves full of binders containing diagrams for dozens of other electronic components.

In addition to the technical drawings of the things he works on, Ulbrich’s shop was filled with the test instruments needed to pinpoint trouble inside of all kinds of pieces sent in for repair. Some of the most helpful ones were a power supply that could deliver the same 28 volts to a unit that an aircraft does, an oscilloscope that allows him to see how electric current is behaving as it travels through a circuit, and a frequency generator that lets him test the receiving capabilities of a voice or navigation radio.

Ulbrich also had a Velcro wristband with a wire attached to it. The band is worn around his wrist and will carry any static electric built-up in his body down the wire and away from any sensitive components he might handle while working at his bench.

Ulbrich’s experience told him that if the AMS44 he was tasked to repair wasn’t getting power, the first place to look for the problem was in the unit’s internal power supply circuits. Using his schematic as a roadmap, he zeroed in on the location of the suspected electronic components. A quick check with his oscilloscope identified the culprit.

"It’s a bad diode," said Ulbrich, pointing to a tiny barrel-shaped part that serves as a check valve to prevent current from flowing in more than one direction in the AMS44’s circuit. "One was shorted and..."

Before he could finish his sentence, an ear-splitting alarm began yelping from one of the many test instruments on Ulbrich’s workbench. When the noise stopped a few seconds later, Sweitzer pointed out of the window toward a small airplane that was parked inside of their hangar. "They’re testing an ELT," he said, referring the technicians whose legs were sticking out from inside a small aircraft. The receiver in the shop is used to verify that the signal is transmitting on the appropriate frequency.

Repair and Service

Once the problem with a unit has been identified, the next step is to determine if the unit is worth fixing. There is no sense in making a $1,000 repair to a device that isn’t worth much more than that, or has a life expectancy that is so short, there won’t be time for the lengthened service life to justify the cost. In those cases, the company or the non-company client will be notified of the situation and, more than likely, the unit will be scrapped and a new or serviceable used one will be obtained.

But the AMS44 with the bad diode on Ulbrich’s bench won’t be scrapped for a new $3,000 unit. "This diode costs 3.8 cents," explained Ulbrich as he rolled the recently removed part around in the palm of his hand. "When I complete this repair, [this AMS44] is going to be out there for years."

Sometimes, the problem can only be tracked to a particular circuit board, but not an individual component. In those cases, technicians can take advantage of the same kind of "plug-n-play" design used by computer manufacturers, where various circuit boards can be easily unplugged, discarded and replaced with new ones from the factory. Sure, it probably means throwing dozens of good sub-components away with the one unidentified bad one, but installing a brand new $300 board in one hour is cheaper than spending six hours hunting for one malfunctioning part at $85 per hour for labor.

Function Testing

Like any other professional repair facility, HTSA performs a function test on everything it fixes and installs. The first phase will be done using the same equipment that was used to diagnose the problem. In the case of the sick AMS44 on Ulbrich’s bench, the replacement diode was tested before installation, and the entire unit was powered up on the bench and connected to a master audio testing panel made by the same company that builds the unit. HTSA’s high-tech test equipment verified that everything was functioning properly, leaving only a simple wipe-down and reassembly operation left to conduct.

The final test would be to install the unit back in the aircraft for a real-world test, but the com panel Ulbrich worked on had become a company spare. The panel will be packed up with its documentation and kept in a supply room until it is needed to replace a bad unit in the future.

Return Shipping

If a repaired unit is to be shipped out, it is placed inside of a special static-shielding bag that helps prevent sensitive parts from static electricity while in transit. (You may have seen one of those metallic coated bags around a piece of new computer equipment you have purchased.)

The item and its associated paperwork is then packed amid plenty of cushioning, sealed up, and sent on its way.

On the other end of the line, the receiving party will find a carefully diagnosed, professionally repaired, fully functioning piece of avionics ready for a hard day’s work. Meanwhile, back at the shop, men like Derrick Sweitzer and Bernie Ulbrich are hard at work repairing troublesome transmitters, unreliable receivers and disobedient displays. It’s all in a day’s work at the avionics shop.

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