At the time, demand for WAAS was uncertain, since few buyers clearly grasped the benefits. Hedging its bets, Garmin did what any self-respecting billion-dollar company would do: It bought UPSAT, including the CNX80 WAAS technology.

The idea was to adapt this to the GNS430/530 product line, but this proved more daunting and time-consuming that Garmin imagined. Garmin delayed certification of the WAAS-capable 430/530 series several times before finally catching the golden ring in early 2007.

Long before it had nailed down the specifics on how these navigators could be upgraded, Garmin offered owners a flat $1500 upgrade. And thats where we are now: Garmin is making good on the promise for WAAS upgrades.

As it upgrades the older navigators, Garmin is also selling new GNS430W and

GNS530W products, which are WAAS-capable from the factory. These sell for $10,750 and $16,495, respectively. Interestingly, the older legacy models are still in the Garmin line, selling new for $9253 and $14,998, respectively.

But new installations of GNS-W versions not part of a swap carry some caveats. It was initially assumed that replacing an existing GNS400/500 series with a new WAAS box or an upgrade would involve simply plugging it into the same tray. But as we venture into these projects on aircraft of all types, were finding more hassles than we and many owners initially bargained for, no thanks to FAA requirements and the demands of executing precision GPS approaches.

We see parallels with CNX80 and GNS480 retrofits, the leftover UPSAT-developed WAAS navigators that require specific installation criteria related to remote annunciation, viewing angles, paperwork and interface with other systems. The CNX80 set the standard for WAAS panel-mounted GPS and the technical aspects carry over to the new 430W/530W line. On the plus side, the GNS-W boxes are blanketed by an AML/STC (approved model list/supplemental type certificate) that covers a range of popular aircraft models, just as the CNX80 and GNS480 WAAS products did. One of the hassles associated with legacy GNS430/530 installations was the need to lobby field approval with a local FSDO. But this practice has been curtailed with the new WAAS units, thanks to the AML/STC. Installers are held to specific standards explicitly spelled out in the new installation manual and in an STC upgrade manual for the installation of the 400W/500W series.

The AML/STC can only be used if the intended aircraft and existing installation are “pre-qualified” as described in the manual. Pre-qualified means ensuring that the aircraft is included on the AML. While there are several hundred aircraft on the list, we found most helicopters, for example, arent on it. If your aircraft isnt on the list, plan on a field approval, with the STC as a basis for the approval.

In doing this, your shop wont be off the hook by any means and will have to ensure that the installation complies with some tedious technical details covered in the manual. Inspectors will use the guidelines in the manual as a basis for their approval. Major items of concern are trivial to perform, but important nonetheless and these may delay the job while the shop waits for the paperwork

First, theres the seemingly simple issue of the antenna. The old units use the familiar Garmin GA56 antenna, but it wont work with the new W boxes. There are several models of suitable TSO-C144 antennas that will work with the new navigators, including the model A34 and A33 designs used with the CNX80 and GNS480.

The A34 is physically the same size and footprint as the GA56, so its an easy install, except for the antenna connector, which must be changed from an existing BNC to a TNC connector. This isnt a major hurdle for any shop but…all of the major connector suppliers are out of stock on these connectors for months as they scramble to complete long-anticipated upgrades.

Garmin admits that this situation is a pain in the shorts and we agree. It would be much easier to unplug the old antenna connector and simply reconnect it to the new one. Other qualified antennas include the Garmin GA35 WAAS antenna and the GA56W and GA56A. We suspect more antenna choices will be available in the future, but for now, the GA35 and A34 are most common.

Pin-for-Pin

From a wiring standpoint, the transition from a legacy box to a new WAAS unit is virtually identical unless certain autopilots and EHSI systems are involved. Even the mounting racks are the same. But, the manuals are specific on areas related to interface wiring practices and the routing of same. For example, inspection of existing wiring and installation of new wiring requires that the pigtail lengths for terminating shields at the W receivers cant be longer than 3 inches. Any deviations must be corrected, which will add time and expense as a result of additional teardown.

Due to cable-loss parameters, low-loss coaxial antenna cable, such as RG400 or RG142 must be used. The manual specifies a cable loss of 3 to 7 dB. In most cases, 3dB worth of loss equals approximately 13 feet of cable run, which allows for a relatively broad range of airframe installations. If your legacy GNS430 or 530 was installed by a rookie and they used cheap RG58 or RG59, it has to be replaced with pricey, low-loss cable. Accessing some interiors to accomplish the replacement will jack up the invoice yet more.

For installations that include the Honeywell Bendix/King KFC225 and KAP140 autopilots, discrete connections from the GNS/W GPS-select output must be added. This will allow for proper autopilot capture of the GPS glidepath while the navigators CDI is in GPS mode. Were finding that this is what many owners value most in a WAAS upgrade the autopilots ability to fly the vertical GPS approach. But getting it wired might require several hours worth of rework, so add a couple of hundred more dollars, at least.

If you have a Sandel SN3308 EHSI and its interfaced to your legacy GNS navigator through a digital ARINC stream, the EHSI wont display the GPS vertical D-Bar due to the SN3308s software. This is supposed to be resolved in the future, but as we go to press, the only fix is to rewire the GNS outputs using an analog interface a step back in time, in our view.

If you have dual SN3308s and dual GNS units in your airplane, youll lose the ability to display vertical GPS and information from either GPS on each EHSI. In our estimation, this is asking for a lot anyway, but we suspect there will be a few gadget freaks who will encounter this catch.

In our view, the second biggest glitch in a WAAS upgrade is that the new box wont crossfill to an older model, since the datacards are incompatible. The crossfill feature is a popular function for many users, especially those who fly a lot of IFR and are accustomed to route changes along the way. Who wants to separately program two boxes when a flight plan changes multiple times? Not us, but thats what youll have to do unless you upgrade both older navigators. Initially, many owners planned to upgrade just the primary box in existing dual GNS panels, but this crossfill surprise changes things.

Those who installed IFR-capable GPS way back when will remember the annoying little supplemental annunciator panels. Well, theyre back and they will be required in some installations. The remote annunciation relates to the position of the navigator in relation to the pilots field of view and the units primary nav indicator, be it HSI, GI106A indicator or something else. The requirements are specific and can be determined with simple measurements of the existing or potential layout.

If the GNS/W is mounted to the right of the primary instruments, “acceptable field of view” means the left edge of the GNS-W bezel is within 13.8 inches of the primary view centerline, which is an imaginary vertical line drawn through the center of the pilots instrument layout. Also, the top edge of the GNS-W series box must be no lower than the bottom edge of the primary flight instruments. Shops will need to measure these centerline distances and determine if remote mode annunciation is required. Many earlier Beechcraft models with avionics stacks displaced to the right will require a set of annunciators.

Mode annunciation for IFR GPS is nothing new because of the FAAs persistent concern that pilots can be unaware of critical GPS data and navigator warning messages when the GPS is out of the pilots central scan. Admittedly, this is the case in some applications where panel layout is non-standard, but for most applications, we think remote annunciation is overkill. In any case, the newly-introduced Mid Continent Instruments model MD41-1488W remote annunciator meets the requirement. Its small enough barely to fit tight panels, measuring 2.5 inches wide and 3/4 inch high. But mode annunciation can also be accomplished using independent lamps–seven per WAAS GPS which might be more of a hassle than going with the integrated MD41, which sells for $647.

This annunciation issue sheds interesting light on the demand for retrofittable PFDs, which can easily contain GPS mode annunciators within their large display areas. Clearly, light aircraft are running out of panel space and PFDs might be the only cure.

We find that AML/STC approval for the new GNS WAAS boxes is a sweet bit of candy with an unpleasant aftertaste. While it can eliminate field approvals in many instances, it holds installers to a strict standard, which means more cost for the owner. The remote annunciation requirement is a snag, since legacy boxes were initially field-approved without them.

Antenna replacements in some airplanes, particularly larger executive-cabined airplanes, will get into some work and expense. One corporate owner told us he was quoted several thousand dollars for the antenna work alone. So, what should you budget for a WAAS upgrade? In addition to $1500 to Garmin, plan on another $800 for a minimal, no-problems installation. If you need annunciators, cable and other work, it will be closer to $2000, but perhaps quite a bit more in cabin class pressurized airplanes. Overall, the upgrade to a new GNS WAAS box wont be difficult work it will just be more involved than initially anticipated, which shouldnt be a surprise.