Battle of the Back-Ups

Are solid-state e-gyros good enough to bail you out of a partial panel jam? We think all of them perform admirably.

by Paul Bertorelli

Notes from a casual conversation with a late-career airline pilot on the subject of flying IFR: With a look of utter horror, our line pilot friend said You actually fly a single-engine airplane in the clouds? On purpose? He shook his head, reeling at the concept.

Not all airline pilots are so divorced from the real world of light aircraft IFR, of course, but those who are got that way for a reason. After years of dual- and triple-redundant everything and back-ups for the back-ups, the thought of boring through the clag with a single gyro powered by an ancient vacuum pump is too unsettling to contemplate.

Even the hardiest of light aircraft IFR drivers worry about gyro failures, however, and thus we have a cottage industry catering to instrument redundancy. There are engine-driven pumps, electric standby pumps, induction vacuum sources, back-up electric gyros and, of late, solid-state electronic flight instrument systems or EFISs.

As we reported in the December 2002 issue, EFIS products have been around in jet transports for years and are now finding their way into light aircraft GA cockpits. And were not talking about $60,000 primary flight displays here, but clever little battery-powered handheld devices that can be slapped on the yoke and pressed into service as back-ups. But do they really work? Yes, they do. And surprisingly well.

Three Systems
For this report, we flight tested three systems: Garmins GPSmap 196 portable, the microEFIS system from Icarus Instruments and the eGyro from PCFlightSystems. The Icarus product uses an attitude-heading reference system built in conjunction with PCFlightSystems and adds to it some display and GPS capability of its own. The Icarus system plays on a variety of PDAs, which can be yoke mounted or Velcrod to the panel.

On its Web site, PCFlightSystems claims its products are the exact same technology used by airliners and that any aircraft…from Piper Cubs to L-39s-can have a full gyro panel. Thats a bit of a stretch.

Although airline systems use solid-state ADAHRs boxes to drive their displays, this equipment is considerably more robust than the low-cost boxes sold by PCFlightSystems and they also provide more redundancy, with multiple power sources and display options. The concept may be the same; the execution certainly isnt.

Beyond that, then, what are the claims for these products? What are they supposed to do? None are, of course, certified under any kind of TSO and none require any FAA approval to install and use.

Garmin makes no claims for the GPSmap 196, other than it being a state-of-the-art portable suitable for supplemental navigation. The 196 has three navigation pages, one of which is called a panel page. This page graphically presents basic flight information, including an HSI, an airspeed indicator, an altimeter, a turn coordinator and a VSI. Its an electronic version of a standard panel, not a virtual EFIS, with instruments driven entirely by GPS, sans gyro input of any kind.

Wisely, Garmin hasnt touted this capability as anything other than a curiosity. In fact, just to look at the panel page, you have to acknowledge this disclaimer screen by pushing the enter key: CAUTION: This information is presented for VFR use only as an aid to prudent navigation. These indicators are based upon GPS-derived data and may differ from the instruments in your aircraft. Translation: dont be a moron and take this thing into the clouds as the only means of remaining upright. To which we add: you could, but you shouldnt.

As for the microEFIS, Icarus says in certified aircraft, the microEFIS is used as back-up to the primary attitude gyro/vacuum system. The microEFIS-and the eGyro from PCFlightSystems-are intended strictly as uncertified back-ups, governed by the gray world of FAR 91.21, the portable electronic devices rule. How much trust you put into them is between you and the manufacturer.

Garmin 196
We reviewed Garmins GPSmap 196 in the September 2002 issue of Aviation Consumer, reporting briefly on the panel page feature. This page is easily accessible by toggling through the moving map page or numerical page with the page key. After dispensing with the disclaimer, the full screen is occupied by the five basic flight instruments described above. In addition, there are numerical repeaters for speed and altitude and values for ETE and distance to active waypoint. That means that on a single page, the 196 provides all the data necessary to remain upright and navigate to an airport or waypoint.

The 196s position-in-space is derived entirely from three-dimensional GPS, including WAAS, which its equipped to receive. Altitudes are GPS altitudes which are heights above the GPS mathematical spheroid, not MSL nor precisely AGL altitudes. The 196s displayed altitude usually jives with MSL altitude within a few hundred feet but descending on this data alone without other information could be fatal. Unless youre having a terrible day, a partial-panel emergency will leave you without gyros but with working airspeed, altimeter and VSI instruments.

Speaking of airspeed, the 196s is GPS-derived groundspeed, not indicated airspeed. The obvious shortcoming here is that in a tailwind, the 196s speed will be higher than indicated and it will be lower than indicated in a headwind. For heading, the 196 uses GPS magnetic groundtrack, not true or magnetic heading.

Although it has no pitch indication other than trends in speed and vertical speed, the 196 does have a simulated turn coordinator, from which bank angle can be surmised, since the aircraft cant turn unless its banked. The turn coordinator has no slip/skid ball; in a wings-level slip, it behaves exactly like a real turn coordinator, showing wings level. It does not, however, respond to initial yaw, as a turn coordinator does.

Garmin has clearly applied sophisticated software and rapid updating to get this display to work right and it does work right. Youd expect some jerkiness in the indications and although theres a bit of that, the needle indications are surprisingly fluid and well damped. Start a bank to the left and the HSI dutifully begins winding around and the turn coordinator airplane banks left. Rolling out produces crisp enough response to hit headings-ground tracks-within 10 degrees. The acid test of these things is to fly them, either in the clouds or with outside references blocked. We did the latter by constructing a cardboard hood that restricted the pilots view to nothing but the 196 panel page, repeating a test Garmin showed us last summer. We wanted to see if a pilot could remain upright and find an airport and land, using only the 196.

He can and did. Our test pilot easily flew assigned headings, climbed and descended to specified altitudes and held straight and level. Because of slight display lag, the ride isnt glass smooth. We noted a slight continuous wing rocking-a 5-degree bank either side of wings level. But headings and altitudes were easily maintained. The 196 has GPS approaches in its databases but even without using these, we were easily able to navigate to the runway centerline at Sky Acres, New York, descend and land in what we set as a 500-foot overcast and 1/2 -mile visibility. We repeated this exercise to another nearby airport, Stormville, New York, with the same results.

Pushing our luck further, we tried recovering from unusual attitudes in various pitch and bank-angle combinations. Our subject pilot-who had never laid eyes on a 196 before this experiment-recovered effectively if somewhat uncertainly. Recoveries take longer than they do with conventional instruments and there appears to be a tendency to overbank past wings level during the recovery, again due to display lag. But even with the overbanking, all of the recoveries eventually damped out to wings-level. In a real-world partial-panel event, the Garmin could keep you alive, in our view, provided it doesnt lose power or satellite lock. If you want to navigate to an airport or fly an approach, youll need to be eyes-closed proficient with the navigator. The workload of flying and navigating while also puzzling out the receivers higher functions is simply too great. A better plan would be to find an exit to VFR weather.

Higher on the food chain in both sophistication and price is the microEFIS from Icarus Instruments, a company best known for niche avionics such as the AltAlert and NavAlert. Icarus partnered with PCFlightSystems, which makes the eGyro, to produce a remarkably capable AHRS (attitude and heading reference system) that displays its output on an ordinary PDA.(PCFlightSystems, by the way, markets its own EFIS called the PCEFIS. It sells for $1595 (plus PDA) and has a rather more complex display than the microEFIS.)

Like the Avidyne PFD technology we reviewed in the December 2002 issue, the microEFIS consists of a box containing three solid-state electronic gyros and three accelerometers, one of each device for each axis, yielding so-called six degrees of freedom. The gyros rely on tiny quartz tuning forks which are highly sensitive to angular displacement.

When rotated about their movement axis, they emit a signal value which can be interpreted as rate of angular change. When the gyros rate of angular change is combined with lateral sensing from the accelerometers, movement in three-dimensional space can be accurately sensed.

The gyros live in a 4 1/2 by 6 1/2 by 1 3/4-inch plastic box thats Velcrod to the floor where it wont be disturbed. A pair of serial cables connect it to an external GPS source and to the PDA of choice. We used a Compaq iPAQ 3955 but the hardware will drive any pocket PC equipped with an ARM processor, including products from Casio, Toshiba, Dell and, formerly, HP.

The gyro box sells for $1495 which includes the software and cabling but not the PDA. Plan on another $400 to $600 for that, plus $100 for the cabling to connect the GPS to the gyro box. The microEFIS can run without GPS input but with it, you can navigate and this makes it a more effective back-up.

The box itself is so light-about 12 ounces-that we wondered why its so big. Steve Silverman, of Icarus, told us that most of the gyro box volume is occupied by foam padding which insulates the gyros from stray acoustic noise. Newer gyros hes working with may reduce the box to a quarter of its present size.

Hooking things up is not difficult but in doing so, were reminded of what we dont like about PDAs: the mess of wiring that clutters the cockpit. For that reason, we recommend that if you opt for this system, wire it in semi-permanently with a dedicated PDA for the cockpit.

Silverman told us hes not a proponent of touchscreen controls for PDAs in the cockpit and we agree. Jabbing at the screen buttons with a fingernail or a stylus is a non-starter, in our opinion. No surprise then that the microEFIS has essentially no controls to fuss with. Theres an exit button and one labeled align which aligns the attitude indicator to the displays horizon line, indicating level flight.

When it comes alive, the system takes 12 seconds to initialize and find itself. From that point forward, its just like a conventional attitude indicator, albeit one with a great deal of additional data if used in conjunction with GPS. As illustrated in the photo on page 6, the basic display has an attitude indicator with bank angle and the standard blue sky/brown earth depiction. If GPS is available, it projects current groundtrack at the top, plus basic nav data on the lower portion of the screen. Theres a tiny turn coordinator depiction and slip/skid ball at the bottom of the display. (Note: because of font problems, the display typography in the photo isnt an accurate depiction of the actual product.)

In open sunlight, we found the screen was bright enough to read although due to glare, the side view is limited in daylight. Its better at night, however. If ships power isnt available, the brightness setting has to be set manually and will consume the iPAQs batteries much faster. Without ships power, expect three hours from the iPAQ battery and about four hours from a 9-volt battery that runs the gyro box.

The gyros response rate is similar if not identical to a mechanical gyro, especially for gentle banks and standard-rate turns. Again, we had no problems holding wings level and turning to GPS-derived groundtrack. The microEFIS is less adept at yanking and banking. High-rate banks and pitch excursions tend to delay its response rate and our attempts at recovery from unusual attitudes were sporting, to put it generously. We did recover, but it took some heroic bank excursions.

Steve Silverman told us this is by design. The microEFIS software is intended to respond rapidly in normal turns and banks as a back-up, not in recovering from upsets. Fair enough; it does that. Its a little easier to interpret than the Garmin 196 and it provides enough information to navigate from a single scan source.

The eGyro is the down market version of these devices, costing $495 retail from PCFlightSystems. Like the microEFIS, it relies on inexpensive solid-state rate gyros but rather than outputting to a display, it has a series of colored lights which the pilot must interpret. The eGyro is tiny by comparison to the other products, measuring a mere 5 by 2 3/4 by 1 inch and weighing only 5 ounces. Its shirt-pocket size and intended to be Velcrod on the glareshield, in the pilots field of vision.

The display consists of one horizontal row of nine lights and one vertical row of three lights. The center shared light is green and the outer horizontal lights are yellow and red.

The idea is that combinations of lights indicate attitude. Three vertical green lights, for instance, indicate level in pitch and bank. A yellow light left of center indicates a developing left bank and so forth. It sounds complex but isnt, once youve taken a few moments to read and absorb the instruction key.

As with the microEFIS, the eGyro is mounted on the glareshield and switched on. It initializes in under a minute and is ready to fly. We found the device to be quite sensitive, especially in pitch. From straight and level, it would occasionally indicate a pitch up-a red light-when the nose was level. A slight nosedown would extinguish the light.

In bank, the device seemed more well damped. Starting a turn, theres a slight delay before the lights on that side of the display illuminate. This reduces the tendency to chase the lights so we didnt find it particularly difficult to maintain level flight, if not exact level flight.

What the eGyro is good at-and is in fact designed to do-is to detect a spiral dive. This it does by illuminating the outermost red light corresponding to the direction of the spiral-left or right-and the pitch-down red light.

Recovery is simply a matter of banking the opposite way and pitching up slightly. The eGyro is responsive enough to provide feedback during this maneuvering but not overly sensitive. Some over pitching and banking is inevitable but its not a deal-killer on overall function.

Picking a winner out of this group is difficult because even though each can be a back-up attitude source, each does it differently. Although Garmin makes no claims for the 196 panel page, we think its the most impressive value of this group of devices because for under $1000, its also a highly capable air and ground navigator. To press it into service as a back-up unit, having it yoke mounted at all times is a must. For some pilots-us among them-yoke mounting is a nuisance. Pay your money and take your choice.

The microEFIS is the most flexible of the three products, if you use the PDA for other purposes, such as general navigation with Control Visions Anywhere Map or other general PDA tasks. (It can run both programs at the same time.)

On the other hand, using that flexibility comes at a price, since youll have to fuss with all the wires and connectors. In our view, this is just too big a hassle to put up with.

We think it makes better sense to just dedicate a PDA to cockpit use, tie off the wiring and let it go at that. In that context, the microEFIS will get the job done and our guess is that its reliable enough to serve as a back-up.Last, the eGyro. While this products blinking lights are somewhat enigmatic, they can be mastered. In conjunction with a turn coordinator-which presumably, youd still have after a pump or gyro failure, the eGyro gives reliable direct information on bank-turn rate, really-and pitch, information were sure would be handy in a partial-panel emergency. For those who fly rental aircraft in IMC, the eGyro could be a good choice.

Also With This Article
Click here to view “Partial Panel: Not So Bad?”
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Contact – Garmin International, 800-800-1020,; Icarus Instruments, 301-891-0600,; PCFlightSystems, 866-472-3347,