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Aircraft Maintenance: uAvionix responds to ‘wet compass challenge'

In a recent article, I tackled the question of why we are still using wet compasses in the age of glass panels, challenging the industry to build a better mousetrap. uAvionix answered the call.

The uAvionix AV-MDI demonstrated at EAA AirVenture Oshkosh in Wisconsin is a modern replacement for the wet compass with many extra features. Photo courtesy of Jeff Simon.

The company arrived at EAA AirVenture Oshkosh in Wisconsin with a demonstration product to display.

Although one could argue that a wet compass is the ultimate failsafe instrument, there are many issues with this centuries-old technology:

  • Compasses are not very stable heading sources, forcing pilots to compensate for acceleration and deceleration, as well as leading or lagging during turns.
  • Accuracy can be poor, especially when affected by nearby electronics. Pilots must compensate by referring to printed deviation cards.
  • Compasses are typically located on or near the windscreen, potentially obstructing a critical portion of the pilot’s view.
  • They require routine and time-consuming maintenance “compass swings” to reduce accuracy issues, especially after any avionics work.
  • Compass fluid eventually leaks or evaporates, requiring additional maintenance.

The solution is an inexpensive, certified magnetic direction indicator (MDI) capable of providing a stable, reliable, and easy-to-use display that a pilot can follow as easily as a directional gyro. Since the FAA specifically allows a certified device to provide supplemental information, you could use that same “electronic compass” to provide all sorts of additional features as well. The only problem? No one produces such a device…at least not when I wrote my previous article.

I’ve known the folks at uAvionix for some time and have been extremely impressed with their ability to produce innovative products in small packages (and small prices to match). I knew that the company already had a tiny, certified magnetometer called AV-MAG that provided magnetic directional data to its AV-30 primary flight display. I also knew that the company had a remarkable little 2-1/4” AV-20 flight instrument that is already certified as a clock and flight timer, and which I use in our Titan T–51D Mustang as a G meter, backup attitude indicator, angle-of-attack (AOA) indicator, voltage meter, and it even has a built-in backup battery.

The uAvionix AV-MDI offers several display options, including a 'Snap' feature to help pilots hold a magnetic heading. Photo courtesy of Jeff Simon.

And so it wasn’t too surprising when my phone rang shortly after the compass article was published. The call was from Shane Woodson, uAvionix’s vice president of general aviation. “I saw your article,” Woodson said. “Let’s talk about your wish list.”

So, what did I wish for? How about a low-cost, 2-1/4” MDI with a built-in clock, timer, G meter, and voltage meter?  “See you in Oshkosh,” was Woodson’s slightly coy response.

If you were fortunate enough to make it to EAA AirVenture in July, you probably got to see the result of this lightning-speed project at the uAvionix booth. The preliminary product is called the AV-MDI, and it includes some pretty amazing features:

  • 2-1/4” MDI.
  • A variety of display options including an arc view, compass rose view, horizontal tape view, and digital view.
  • Options that emulate a real compass (turn right – tape moves left), or simplified view (turn right – tape moves right).
  • “Snap” feature that marks a selected heading and provides color indications when you turn off course.
  • Slip/skid ball display.
Photo courtesy of Jeff Simon.

Pricing and a formal commitment to production were not available at the time of the show. However, judging by the crowd of pilots standing around the AV-MDI display, I’d say that uAvionix already has a winner on its hands. If this product makes it to market, I’ll be first in line to yank the compass off the top of my panel, clean up my view out of the windscreen, and say goodbye to practicing “Accelerate North, Decelerate South” or “Overturn North, Underturn South”. I’ve already got a place in my office set aside to display the old compass…right next to the wind-up clock I pulled out years ago. Until next time, I hope you and your families remain safe and healthy, and I wish you blue skies.

Jeff Simon
Jeff Simon
Jeff Simon is an A&P mechanic, IA, pilot, and aircraft owner. He has spent the last 22 years promoting owner-assisted aircraft maintenance and created the first inspection tool for geared alternator couplings available at ApproachAviation.com. Jeff is also the creator of SocialFlight, the free mobile app and website that maps more than 20,000 aviation events, hundred-dollar hamburger destinations, and also offers educational aviation videos. Free apps are available for iOS and Android devices, and users can also visit www.SocialFlight.com.
Topics: Aircraft Maintenance, Avionics
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