AOPA Get Your Glass Sweepstakes Update -- Backing up the power

March 25, 2013

Sweeps Update

Project Update: July 3, 2008

Backing up the power

By Ian J. Twombly

So you bought an Aspen Avionics EFD1000 primary flight display? Congratulations. The question must be running through your mind, like it is everyone else who decides to outfit their aircraft with an instrument source powered by the electrical system—what happens when the power goes out?

Pilots who fancy themselves from the old guard scoff at the idea of glass. Among its many drawbacks, they say, is that you are putting all your eggs in one basket. Traditional aircraft instruments, or so-called steam gauges, are usually powered from two or three different sources, creating automatic redundancy. If the attitude indicator fails, there’s also the turn coordinator, wet compass, and altimeter. A turn coordinator failure hardly warrants a second thought, except—since it’s electric--it likely means you’ve just lost your radios as well, unless it’s a gyro gone bad. The idea is that the failure of one system doesn’t mean all the instruments will fail.

Not so with glass cockpits. The Aspen PFD is powered solely by the aircraft’s electrical system. So, unlike an electrical failure in a steam gauge-equipped airplane, the same failure in the AOPA Get Your Glass Sweepstakes Piper Archer would mean losing the primary source for all six flight instruments (attitude indicator, heading indicator, altimeter, turn and bank coordinator, airspeed indicator, and vertical speed indicator). At least, it would eventually mean losing all six instruments. Because the Aspen has a built-in backup battery, the display would continue to shine on for another 30 minutes.

Is there a problem?

Because we want to deliver the safest and most useful airplane possible with each sweepstakes project, we went on a hunt for some piece of mind. The Aspen is a new product and new products are notoriously finicky. Plainly, we didn’t want an electrical problem in the airplane to lead to a major emergency. So we went about assessing what we had and what we wanted.

We had an electronic display for the primary six instruments. We also had a backup altimeter, attitude indicator, airspeed indicator, wet compass, and turn coordinator (required for the autopilot). The altimeter and airspeed indicator remained on the pitot static system, the turn coordinator is still powered electrically, and the attitude indicator still operates off the vacuum pump. Of course, the Aspen also has the battery backup. What all that means is if the airplane’s electrical system decided to take a holiday, the pilot would still have at least 30 minutes with the primary flight display. If that isn’t enough time to get to visual conditions or to land, there would still be other backup systems to get down safely.

It was then time to assess what it was we wanted. If possible, we wanted a redundant source for electrical power. We started to look for options. To completely relieve any suspense, let me begin by saying there aren’t many. Theoretically one could add a second alternator and another battery, a stand-by alternator, a ram air turbine, and not much else. It only takes a second to realize that the 30 pounds of an additional battery alone hardly makes the potential benefit worth the drawback. Add in the complexity and certification issues, and you can see why no one (I’m making an assumption here) flies around an older Piper Archer with dual batteries.

On the other hand, a stand-by alternator is a viable, relatively inexpensive option. While many are available for the experimental market, I’m aware of only one company producing them for the certificated aircraft owner. B&C Specialty Products sells a certified stand-by alternator for the Beechcraft Bonanza, Cessna 210, and Piper PA32 line. The alternators fit in the back of the engine on an open “pad.” The reason one isn’t available for the Archer is because the Lycoming O-360-A4M doesn’t have an open pad in this application. So while we may have been able to ditch the vacuum pump—and invoking a completely different set of challenges in the process—and use its pad, we decided against the paperwork and certification headache. And while we did look into the ram air turbine, or RAT, it just didn’t seem to fit the scope of the project, although one was supposed to be certified by the time we would have installed it.

As you can see, all that put us back at square one. And in the end, we’re OK with it. Now, things may have been different if we were talking about installing two Aspen displays. With two displays, there’s no requirement to have backup instruments, thereby making the entire panel a slave to the electrical system. It’s an interesting future.

As a side note, the airplane had a standby vacuum system installed when we purchased it. So while we don’t have backup electric, we do have a backup for our backup instruments.

Next week: The makings of a good panel upgrade

E-mail the author at ian.twombly@aopa.org