If you’re stepping up into the world of higher-end twins and some high-flying singles, you’ll eventually be faced with maintenance of onboard weather radar. Upgrading and maintaining weather radar is an expensive investment, and the benefits of real-time ship’s weather radar might not be obvious to today’s datalink pilot. But resist the urge to yank ship radar from the airframe—it still has its place.
On a recent trip up the East coast in a small twin, we were picking our way along the back edge of a slow-moving line of Gulf-fed buildups that offered no shortage of drama for hundreds of miles. It was a tense flight, but tempered by the NEXRAD images steadily arriving from XM.
But as we motored closer to a large cluster of buildups, XM’s image just wasn’t jiving with our view through the windscreen. A watchful controller then offered a heading through a gap that would have been through the heart of a red NEXRAD return. However, overlaying a stabilized image from the Bendix/King radar on the MFD moving map confirmed just what the controller was painting: a comfortable path that NEXRAD said didn’t exist. That’s how ship’s radar earns its keep.
Ship’s Radar 101
Pulsed radar locates targets by transmitting a microwave pulse beam that reflects off precip and back to the radar receiver as a return often called an echo. The microwave pulses are focused and radiated by the system’s antenna, located in the nose of twins or enclosed in a wing pod on singles. The same antenna is used for both transmitting and receiving.
The returned signal is processed and displayed on either a dedicated radar display, or as a remote input to an MFD. The MFD option has been the saving grace for a mostly stagnant GA radar market because the color MFD has greatly enhanced the display and effective usefulness of aging systems.
Still, it’s not all roses. An accepted limitation for small airplane radars is the diameter of the antenna, which is limited by the radome you have to fit it inside. The radar beam is much like the beam of a spotlight; the farther the beam travels, the wider it gets. The smaller the antenna, the wider the radar beam and the more its energy is dispersed over each mile it travels away from the aircraft. A 10-inch antenna (the size you’ll typically find stuffed in a wing-mounted pod) has a 10-degree beam. A 30-inch dish in the nose of your average airliner shoots a three-degree beam.
When scanning longer distances with a smaller antenna, a storm won’t fill the beam’s entire width. Energy is lost as it moves past areas where water droplets reflect it back. A small-dish radar sniffing out 100 miles might paint a puny return for the pilot that is, in fact, a Level-6 disaster waiting to happen. Wide-beam radar needs to be closer to the storm to assess it accurately. Talk about the proverbial cat in a room full of rocking chairs.
Bendix/King RDR2000
Honeywell’s four-color RDR2000-series digital radar came trickling down from its higher-end system’s years ago. The higher-powered RDR2100 system adds a 120-degree scan plus an auto-tilt feature that smartly manages tilt angle while the aircraft climbs or descends. But Honeywell no longer sells this system with a dedicated display, expecting you to use a KMD850 or Avidyne EX-series MFDs. The systems sans display are the ART-2000 and -2100 for $22,682 and $42,186, respectively.
The 2000-series is a solid-performer that’s been used extensively as original and aftermarket equipment in everything from Beech Barons to turboprop singles and twins. It was also an integral component with the Honeywell IHAS integrated hazard awareness suite, overlaying weather on the KMD850 MFD. There’s an EFIS interface for older glass panels, and software is in the works to play on the new Avidyne IFD540, which replaces older Garmin GNS 530s.
The ART-2000 is stabilized, which means it gets a pitch reference from an attitude gyro or AHARS source. This stabilization is an important part of seamless radar operation, keeping the picture in proper orientation with the aircraft’s nose. The ART-2000 makes 4 KW of peak power and has a vertical profile mode.
This vertical profile feature made the RDR2000-series a big seller for Bendix/King and on the used market. It still remains one of the more sought-after radars for light twins and turboprops. It’s a proven performer, with a 227-nautical mile range and a magnetron (what actually generates the radio energy) with an advertised 8000-hour average life. That’s a long time in the life of magnetrons.
The RDS-81 model was good radar in its day, but we’re seeing more failures as these systems age. A popular fix is to bolt the ART2000 in its place. The interface connector is different, so you’ll pay for some wiring work.
We spoke with a couple of respected radar shops, including Duncan Avionics and Fieldtech Avionics, and got the impression there’s still reasonable repair support for the RDR160 and RDS-81, but the RDR2000 series is clearly the favorable upgrade on the used market. Healthy, lower-time RDR2000s earn impressive dough—over 10 grand in many cases.
Garmin GWX 68
Believe it or not, Garmin’s $20,995 GWX-series digital radar started life as the once-popular general aviation King KWX58. In the late 90s, Garmin purchased the KWX, if only for an R&D building block. The brilliantly re-engineered system sports a magnetron with 6500 watts of transmit power. (See the sidebar for the just-introduced GWX70, a solid-state descendant of the GWX68.)
Like other remote units in Garmin’s modern line of glass cockpit technology, the GWX 68 is considered a Line Replaceable Unit (LRU) with an open architecture that outputs weather radar data to an external MFD, including the GMX200 Radar MFD, G600 PFD/MFD-combo (or G500 with an enablement card), G900X and G1000 avionics suites and the GTN750 navigator with version 3.0 software. The GWX 68 communicates with other LRUs in the suite using ARINC 429/453 or Ethernet.
A flat-dish design, the GWX 68 is offered in 10- and 12-inch antenna sizes to accommodate a wide variety of light twins and high-flying singles and is stabilized. There’s also a feature called sector scan. With user-adjustable scan angles of up to 90-degrees, scanning sectors is helpful for a focused look at storms in a given sector. Vertical scanning looks up and helps to analyze storm tops, gradients and cell buildup activity at higher altitudes.
Garmin tries hard to overcome the shortcomings of magnetron-based radar with what they call Weather Attenuated Color Highlight (WATCH). This helps to identify where return echos are weakened by intense precipitation and may not fully reflect weather that exists beyond what’s being painted. The GWX68 is always at work with a Weather Alert mode that looks ahead for intense cell activity up to 320 miles out, even if the pilot isn’t monitoring returns at that distance.
MFD Boosts Performance
While failures of a radar trans-ceceiver might be more common than display failure, a faulty CRT is usually a throwaway. Moreover, old monochrome technology isn’t exactly your ticket to modern cutting-edge weather mapping.
Saddling an existing radar with a MFD is an easy ticket to jumpstarting the older, but otherwise healthy, system. Avidyne offers the most MFD/radar combinations. The drill is to install a pre-fab radar interface cable between the existing radar and an Avidyne EX600 (or older EX500). An adapter board and software inside the MFD create a dedicated radar page and an overlay on the MFD moving map—a real gain in utility compared to a standalone screen. However, the MFD must have a heading signal for proper weather orientation. An AHARS-feed or 400 Hz analog synchro signal from an HSI will do the job.
Garmin’s new version 3.0 software for the GTN750 touchscreen navigator enables the play of ARINC label 708 digital radar, including Honeywell’s ART2000/2001 and RS181, as we’ll as Garmin’s GWX-series. This real-time weather overlay includes the vertical scan functionality. Given the suitability of the GTN-series for a wide variety of aircraft, this new interface opens up a huge opportunity to play ship’s radar in aircraft that can accommodate a radome. There’s no radar overlay on the smaller-screened GTN650.
Decision Time
Whether to repair or remove your aging radar really comes down to mission need and the age of the gear. We wouldn’t sink real money into anything older than an RDR2000, or perhaps an RDS81 if a qualified shop blesses it as a keeper. For those units, though, we think it’s worth keeping, especially if display on an MFD is an option.
Buying new? Our experience over time with the GWX68 has convinced us that it offers solid performance and reliability that’s priced right. For bigger turbines, the new GWX70 seems the logical match.
Lastly, we think Garmin’s new GTN750 radar-enabling software will solve a huge problem for a lot of owners who otherwise go without radar because they don’t have space for a MFD. There’s a sizeable investment involved installing a GWX68 or 70 but we think it’s smart money for high-flying and go-places aircraft with a place to put the antenna. In fact, a GWX+GTN750 combo might be the ship radar for GA to date.
