In the clouds with space vehicles
As the Global Positioning System continues to mature and become an indispensable part of our navigational repertoire, much attention has been focused on the instrument-flight-rules approval of many stand- alone and multisensor panel-mount receivers. In concert with the proliferation of moving-map displays, the transition to en route, terminal, and approach approval according to Technical Standard Order (TSO) C129 has been the big news. (The other GPS hot spot is, of course, the inexpensive and tremendously capable handhelds.) Today, the majority of the GPS manufacturers already have en route and approach units on the shelves, and a few more have approval pending. All are, to some extent, preparing for WAAS (wide area augmentation system) to come on line and provide differential correction that will make GPS suitable for precision approaches. But we're not there yet. So, what does instrument approval mean for buyers today? Depends upon what's in the airplane now. If you've got a panel full of radios and the equipment to file "slant romeo," the IFR-approved GPS in reality buys just those approaches served only by the satellites. Currently, there are about 5,000 GPS approaches in the United States. All but approximately 400 of those are overlay approaches, basically mimicking the procedures set by the ground- based navaids. Of those, about 40 percent are Phase II approaches, meaning that you must have the equipment to use the underlying conventional approach, although you can be using the GPS as your primary guidance. Phase III approaches need only the proper GPS receiver to be used legally, and the underlying approach aids may even be notam'd out of service. About 400 of these approaches are clean-sheet, GPS-only versions with no conventional underlying approach; that number is expected to rise to 500 by the year's end.
The approved GPS does, however, offer a more accurate means of shooting those nonprecision overlay approaches and will allow RNAV-style direct routings without the VHF-based equipment.
Upon glancing through catalogs, you'll notice a great price disparity between similar IFR and VFR models — sometimes by a factor of two. This difference represents a manufacturer's way of recouping extensive TSO-approval costs, as well as an understandable tariff on the additional software and hardware requirements of approach approval. What's different? First, the IFR- approved box must have RAIM (receiver autonomous integrity monitoring), which is a software routine that ensures flagging of the navigation display if there's any question about a position fix. Common GPS receivers will also flag when satellite lock is lost, but the RAIM requirements are far more stringent. In addition, the TSO C129 radios must also have something called predictive RAIM; this feature looks ahead to your planned flight and, using stored satellite-position data, determines whether there will be sufficient satellite coverage for operation within IFR parameters.
But just purchasing an IFR-approved GPS receiver is only part of the package. These days, a full installation — which requires sophisticated switching and annunciation modules and connections to many of the airplane's existing instruments — can add $2,000 or more to the basic cost of the GPS. Here's where you need to shop for your avionics store carefully. Ask around — find out which GPS your shop installs most often. These IFR packages are not trivial slap- ins, nor is completion of the paperwork a five-minute job. Instrument-approved receivers are installed under a multiple STC (supplemental type certificate), and many FAA regional offices require flight testing to prove the installation. You may be asking for trouble — and paying for plenty of on-the-job training — if yours is the first installation of a given box by that facility. Also, budget for frequent database updates for your IFR model — on the order of $500 a year.
Plan also to spend time getting to know your IFR GPS and the specific approach procedures. While satellite navigation is far more accurate than most of the familiar ground-based aids, shooting GPS- based approaches is not as easy. Care must be taken to understand the GPS receiver's various approach modes and to become familiar with the routines regarding external annunciation and indicator switching. And because of the differences in each manufacturer's methods of complying with the TSO, don't assume familiarity with one maker's box will transfer to another's.
Whether IFR or plain old VFR, today's panel-mount GPS receivers contain feature sets that are nothing short of stupendous. Airport and navaid information galore, including runway diagrams, is common; and the IFR-approved units all have en route and approach- related intersections built in. Most of the GPSs use parallel receivers with as many as 12 channels — meaning that up to 12 satellites can be tracked and monitored simultaneously. Garmin is the notable exception; the GPS 155 uses the firm's proprietary MultiTrac 8 scanning receiver that can track up to eight satellites.
Here's a sampling of some of the boxes available today.
An early leader in the loran field and a major proponent of loran for IFR, Arnav Systems fields two very similar GPS receivers, the Star 5000 and the FMS 5000. The Star 5000 uses an internal five-channel GPS engine, while the FMS 5000 can be mated to one of two (five- or 12-channel) external GPS receivers. The FMS 5000 is currently certified under the multisensor TSO for en route and terminal IFR. Both models of the 5000 use a bright, two-line dot- matrix display and direct-to menu buttons on the front panel. Since this machine's beginnings as the R-50 loran in the late 1980s, Arnav has continued to tweak the operating system to make it become more friendly to pilots. Suggested retail price for the stand-alone Star 5000 is $3,995, while the FMS 5000 starts at $4,495 with the five-channel receiver.
From a newcomer to aviation but an old hand in the surveying industry comes the Ashtech Altair AV-12, a 12-channel GPS receiver with a color CRT display and sophisticated moving map. This receiver had been on the "coming soon" list for some time but became available this summer. It combines a complete Jeppesen database — as do most of the GPSs on the market today — with an extensive listing of airport and navaid information.
What really sets the Ashtech apart from the rest of the field is its color CRT display. Only it and the Bendix/King KLN 90B (in monochrome form) use these CRTs, but many users feel the excellent resolution and flexibility of the displays make up for the cost. Ashtech's combines the usual navigation information with a full- feature moving map, complete with special-use airspace. We've sampled the Ashtech's map at various trade shows — but not yet in any airplane — and have been impressed. The color coding of waypoints and airspace helps to reduce screen clutter tremendously. Ashtech's AV-12 is not yet approved under TSO C129 for approaches, but the company says the current box is fully upgradable and will accommodate WAAS for precision approaches later on. Suggested retail price is $8,500.
With its roots way back in the KLN 88, probably the most sophisticated loran ever made, the Bendix/King KLN 90B GPS represents the culmination of the firm's tweaking of this family of navigators. Currently approved for IFR en route, terminal, and nonprecision approaches, the 90B retains the moving map and nearly overwhelming amount of ancillary information of its older brethren. The 90B's map is useful for position awareness and for showing the segments of the approach; and the CRT display helps to give the display tremendous flexibility.
The KLN 90B uses a data cartridge mounted behind the unit, but the extensive database can be updated from floppy disks with a PC and data-loader cable. As one of the most capable GPS receivers around, the KLN 90B is also one of the more expensive, at a suggested retail price of $8,495.
Garmin's GPS 155 is the IFR-approved outgrowth of the firm's panel-mount GPS 150 . Using a four-line, dot-matrix display, the Garmin 155 also complies with TSO C129 for en route and nonprecision approaches. Its Jeppesen-compiled database goes in through a front-panel slot and contains the normal navigation information in addition to a plethora of facility and airport radio frequencies. An uncommon feature of the 155 is its built-in battery backup, which can keep the 155 navigating for up to two hours in the event of power loss, according to the company.
Garmin is currently selling the 155 for $4,995, with a special annunciator package running an additional $799. Through the end of January, with the purchase of the 155 Garmin will also throw in a GPS 90 handheld or a one-year database update schedule.
Magellan Systems says up front that it has no intention of certifying the Sky Nav 5000 under the current IFR TSO. Instead, it will parlay experience, developing its new CNS-12 high-end flight- management system into a new IFR receiver. That means the Sky Nav will remain a VFR receiver. Magellan says that a relatively inexpensive upgrade path to the IFR-certified receiver will be available to owners of the Sky Nav.
Even without IFR approval, the 5000 comes to the party with many desirable features, including a bright fluorescent display and front-panel database card. The Jeppesen database includes all U.S. airports with runways longer than 1,000 feet, as well as VORs and NDBs. The Sky Nav also packs a five-channel parallel receiver. As is true with many of these panel-mounts, the Sky Nav includes a data- out port to drive moving-map displays, and it can also drive external course deviation indicators or HSIs. Suggested retail price is $1,899.
One quick look at the Northstar M3 and you might think the company has changed its products little since the M1 loran days. And while it's true the M3 is externally quite similar to the M1, there's little that is familiar inside. Today the M3 is is driven by a 12- channel parallel GPS engine and is approved for IFR en route and terminal navigation. Northstar says that approval for nonprecision approaches will be coming by the first quarter of 1996. The upgrade will be a no-cost feature for current owners of the M3.
Like the M1 before it, the M3 uses a single-line LED display. You can also upgrade the M3 to SmartComm status, which adds an external 760-channel com radio. Suggested retail price for the M3 is $6,395, and the SmartComm option adds $1,995 to the tally.
Another firm with a panel-mount on the cusp of IFR approval is II Morrow with the Apollo 2001 GPS. According to the company, the 2001 will be approved for nonprecision approaches by the first quarter of 1996. Part of the delay, according to the company, stems from its seeking a slightly different approval track. Instead of the usual connections to the CDI or HSI, II Morrow is seeking approval without the need for so-called resolver input. This is the signal sent back from the CDI or HSI to tell the GPS which course has been selected. (Trimble has successfully traveled this road; see below.)
Otherwise, don't expect too many changes to the 2001, which can be had in either stand-alone eight-channel GPS form, or with the already-certified loran sensor on its networked data line. As before, the 2001 uses a three-line dot-matrix display and a front-panel Jeppesen data card. Suggested retail price for the current VFR-only 2001 is $3,995.
Trimble has been continuously developing the TNL-2000 line and the latest offering is the TNL-2000 Approach. Certified for both en route and nonprecision approaches, as the name implies, the 2000 Approach continues to use the previous 2000s' twin-line display and front-panel Jeppesen data card.
As mentioned earlier, the Trimble Approach package includes a provision that could result in somewhat simpler installations than the other IFR receivers listed here. In seeking compliance with the TSO, Trimble managed to convince the FAA to allow course-setting cues to be entered on the receiver's main display, as opposed to being done remotely through the CDI or HSI. Depending on the brand and capability of the indicators already in your airplane, this could ease installation.
Trimble's current price for the TNL-2000 Approach, which contains a nine-channel parallel receiver, is $5,995. There are also several upgrade schemes to trade from other Trimble units to the TNL-2000 Approach, costing as little as $1,500.
It should be clear from the offerings here that the panel-mount GPS market is maturing quickly. With any luck, the current trend of ever-greater sophistication will be met with ever-decreasing prices. That way we'll all be winners in this extraterrestrial gambit.
