Marrying into a moving map family
With the acquisition of the Terra line of avionics now complete, Trimble joins Narco and AlliedSignal as the only companies offering complete radio stacks to general aviation. With a virtual lock on the new aircraft market and a strong presence in all general aviation aircraft built in the past 15 years, there is no doubt that AlliedSignal's Bendix/King product line rules. Particularly in IFR GPS shipments, AlliedSignal seems almost untouchable. Nonetheless, Trimble is making inroads. It recently became the official avionics manufacturer for Cirrus and is in discussions with virtually every airframer out there.
With 10 to 20 percent of the IFR GPS market, Trimble's 2000 Approach unit has held its own against units from Garmin, II Morrow, and, now, Northstar. However, Trimble's higher- end GPSs for the commuter market and retrofits for older jet transports have gained wide acceptance.
AlliedSignal has held onto its lead in the general aviation market by being the only manufacturer to offer a complete line of GPSs with moving maps built in. When one is flying a complex procedure such as a nonprecision approach, a picture really is worth a thousand words in maintaining positional awareness. To make up for its lack of a moving map, Trimble has partnered with Eventide to package an Argus moving map with the 2000 Approach. Together, the two units sell for about the price of the Bendix/King KLN 90B, which has a built-in map. The standalone 2000 Approach lists for $4,895. Add an Argus 3000 and the price climbs to $7,890; substitute an Argus 5000 and the price jumps to $9,890. The KLN 90B lists for $8,595.
Trimble provides a number of upgrade paths to those customers who own its VFR receivers. Those worried about obsolescence can rest assured that Trimble offers an upgrade path from the 2000 Approach's nine-channel receiver to a 12-channel receiver with wide area augmentation system capability, for installation when that system comes on line in the next decade.
The combination of the 2000 Approach and the Argus provides terrific positional awareness during the approach; watching it depict and then fly the DME arc portion of the approach will give goose bumps to any technophile.
The disadvantage of the Trimble/Argus combination is that it requires not only a place in the avionics stack, but an instrument hole as well. Trimble officials counter that by saying that you can put the Argus in your main scan, making the moving map even more valuable.
No matter the unit involved, expect to spend about $2,000 installing an IFR GPS. Trimble reduces the installation sting a bit for some customers by eliminating the need for a resolver unit to convey the setting of the external omnibearing selector back to the GPS. Technical Standards Order C129, under which all approach-capable GPSs are certificated, requires that the units be connected to an external CDI located in the pilot's scan. The electronic CDIs on the units themselves cannot be used for the approach. Further simplifying the installation, the 2000 Approach needs no external switches; just a small annunciator panel is required. Installation of an Argus will probably negate any of these savings.
Like the rest of the IFR GPSs available today, the 2000 Approach offers excellent accuracy, a database brimming with features, and an easily readable display. Pilots shopping for an IFR GPS should buy first on functionality and then on price. All of the IFR units have demonstration or simulator modes, so it's easy to bench fly each of them at your local avionics shop.
While the 2000 Approach can display only two lines of data, it makes good use of those lines by allowing the pilot to customize them. Display about anything you want on either line; you can even display bearing, distance, and time to a second waypoint on the second line.
While there's been no small amount of grumbling from the pilot community over the complexity of flying GPS approaches, standalone and straight-in overlay procedures can be quite simple, provided ATC throws you no curves. The confusion factor rises only when you must fly a course reversal or when ATC switches the initial approach fix at the last minute.
To fly a straight-in approach, for example, a pilot need only select the approach from the database. Unlike some of the other receivers, the 2000 Approach gives the pilot the opportunity to select the procedure directly; the same with SIDs and STARs. Other receivers require the pilot to select the airport and then choose the approach or SID/STAR from a submenu. The Trimble, though, offers approaches as a database choice, along with airports, SIDs, STARs, VORs, NDBs, intersections, and user-created waypoints. If one is using a flight plan, the approach waypoints will be added to the end of the flight plan.
Once the desired approach is displayed, the pilot can then slew through the approach waypoints to choose the desired initial approach fix. From there, hit the Direct key and go back to the Nav page to navigate to the fix. When the airplane is 30 nm from the airport, the system will automatically inquire: "Approach enable?" and suggest the ENT key. Throughout the operating system, the 2000 Approach is good at suggesting which key to hit. At the same time, the system requests that the current barometric pressure setting be entered.
From there on, it's just a matter of flying the waypoints to touchdown.
At 2 miles from the final approach fix, the APR annunciator lights to remind the pilot that the system is functioning normally in the approach mode. If a missed approach is necessary, the pilot simply pushes the Direct key twice at any point after the final approach fix and the unit will lead the way to the missed approach waypoint.
Things get a bit more complicated when the aircraft is flying an approach that requires a procedure turn or hold. In those instances, the pilot and the receiver must know whether to sequence through the list of waypoints or to stop the sequencing at some point while a procedure turn is flown. Unlike some of the other approach-certified receivers, the 2000 Approach applies logic to the hold/sequence issue.
Some of the other receivers require the pilot to switch the receiver to a Hold mode manually prior to crossing a fix outbound for the procedure turn and switch it back into a sequence mode when turning inbound. Otherwise, the unit would attempt to sequence the pilot directly back to the final approach fix when he's still outbound.
The Trimble, though, goes into a hold mode automatically if the track being flown differs from the final approach course by more than 70 degrees, as it generally will if the pilot needs to fly a course reversal of some kind. Once crossing the fix outbound, the system then requests that the pilot enter the course to be flown for the procedure turn. Most pilots may well ignore the step and simply fly the depicted course reversal without navigation system guidance.
Once turned inbound and within 70 degrees of the final approach course, the system will request the pilot to "Enter FAF Inbound Course." Typically the suggested course is the correct one, so it's just a matter of hitting the Direct key.
Of course, the pilot has the option of manually entering the Hold mode at any point and staying there if a holding pattern is necessary.
When paired with an Argus moving map, the 2000 Approach makes a DME arc approach look deceptively easy. The Argus displays a series of linked segmented lines that form the arc as outlined in the approach procedure, leading the pilot to the turning waypoint and then inbound on the final approach course. While it may be tempting to ignore the Trimble's display and simply fly left or right to keep the little electronic airplane on the Argus' depicted arc, you'll fly it more accurately by also watching the GPS's display. During the approach, the Trimble's navigation page shows the active waypoint at the end of the arc and the bearing and distance to it, along with the all- important desired track to remain on the arc. Also depicted are a CDI, cross-track error, the identifier for the station upon which the arc is based, and the DME distance.
As you might imagine, it's a lot of information to absorb, even with the pictorial help from the Argus.
Pilots take months to learn to fly DME arcs or any other IFR procedure the old- fashioned way — and years to perfect the techniques. GPS offers uncanny accuracy and a helpful database full of information, but don't expect to master such a powerful tool on only a flight or two. The same common sense that applied when you first learned to fly VOR or ILS approaches applies to flying GPS approaches. Whether you're using a Trimble 2000 Approach or any other IFR GPS, fly approaches in actual conditions only after practicing extensively in VMC. Even then, fly the first approaches in "light" IFR, when you know the ceilings are high and visibility is good and when you have a convenient alternate with a conventional approach.
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