I WAS LANDING FOR FUEL at Kinston, North Carolina, and the weather was 300 feet overcast with one-mile visibility in light rain. The Garmin G600 flat-glass avionics had been in my Baron for only a few hours, and it was my first chance to fly an instrument approach in low conditions.
Though I have done this many times before and know that there is a runway — a very long one in this case — at the end of every ILS if you just keep the needles centered, the G600 made a huge difference. Yes, the needles still needed to be centered, but at every moment during the approach, the G600 showed me information that I never had before in my aging airplane.
Probably the most dramatic change is the synthetic vision technology (SVT) picture on the primary flight display (PFD). In addition to seeing a centered localizer and glideslope, I watched the image of the runway loom ahead even though I was in solid cloud and rain. There was a little crosswind, so the nose of the airplane was not pointed directly at the runway. But the flight path marker that shows where the airplane is going, not where it's pointed, remained right over the touchdown zone of the runway.
It's pretty flat around Kinston, so there was no high terrain to see between me and the runway, but if there had been, or if I had descended too low on the approach, I would have seen a synthetic view of that terrain too. I may not be the ace of the base, but I do believe that I will not fly into terrain that I can see, whether with natural or synthetic vision, so that has to be a big safety edge.
The weather report was pretty accurate and, as I neared the decision height, I could start to see the actual runway environment appear. By that time the synthetic view was showing runway details such as the centerline and other markings, including the runway number. The synthetic view and the gauzy view of the actual runway through the rain and mist lined up perfectly.
I had flown syn viz displays in a number of airplanes before with avionics from different manufacturers, but this was my first chance for a low approach in actual weather, and it's even better than I imagined. Syn viz may not be exactly perpetual VFR, but once you fly with it, taking it away is like going on partial panel. I never expected to see such capability in my lifetime, much less available for older piston airplanes, but the G600 has it and a lot more.
A Complete System
The G600 is a complete flat-glass PFD-MFD system designed for retrofit in airplanes equipped with conventional instruments. The PFD and MFD displays share a common mounting case that fits into approximately the same instrument panel space occupied by the common "six-pack" of primary flight instruments.
Supporting the G600 function are the attitude-heading reference system (AHRS) with its nonmoving gyros, and a digital air data computer (ADC) to measure airspeed and altitude and to calculate all other air data information, including vertical speed and true airspeed, and supply the necessary information for real-time winds aloft display.
The G600 system also contains an altitude alerting system and the roll steering commands for the autopilot so the system can automatically fly complete instrument procedures. Additionally, the system can display all manner of traffic, weather and navigation information on the multi-function display (MFD), with crucial information such as traffic warning also on the PFD.
The G600 has been certified and available since last year, but I was waiting for a final approval that is very important to the thousands of airplane owners with autopilots in the Bendix/King KFC family, and to others with autopilots that use attitude information to operate. That crucial certification that Garmin received last fall is for the AHRS system in the G600 to replace the spinning metal gyro in the auto-pilot system.
For the earlier G600 installations, pilots with attitude-based autopilots had to keep the spinning gyro in the panel in a prominent location. That old-fashioned gyro supplied the necessary attitude information for the auto-pilot to operate, while the advanced and superior AHRS was restricted to showing attitude on the G600 PFD. If the spinning gyro failed, so did the autopilot. And the rather frequent maintenance and overhaul requirements of the spinning gyro continued even though you had the electronic AHRS in the airplane.
Now the G600 certification allows the AHRS to operate directly with the autopilot. The autopilot — a KFC-200 in my airplane — gets the much more precise pitch and roll information from the AHRS, which also supplies heading, thus eliminating the compass system and its own spinning gyro. The only conventional gyro left in my panel is a basic three-inch attitude gyro for backup. Because I still need the vacuum pumps to power the deice boots, I also use that air pressure to power the standby gyro.
So far the G600 is the first flat-glass retrofit system capable of eliminating the autopilot and compass gyros in attitude-based autopilot systems, which are common in high-performance piston airplanes and even turboprops, such as the Cessna Caravan fleet, and other airplanes weighing as much as 12,500 pounds for takeoff. Getting rid of the spinning gyros with their maintenance and overhaul costs is a huge advantage for both dispatch reliability and costs, as well as in performance, because the AHRS is more precise.
Replacing the gyros isn't an issue for airplanes equipped with S-Tec auto-pilots, because those systems do not use attitude information. S-Tec uses a turn coordinator gyro along with static air pressure changes to control the airplane, so you will see no change in performance or precision of the S-Tec autopilot with a G600 installed.
The key ingredient that makes it possible to link the G600 and its AHRS to a legacy autopilot is the Garmin GAD 43, a magic box that allows old and new systems to communicate. Spinning gyros create an analog reference voltage to tell the autopilot the airplane's attitude, but the AHRS sends out a digital electronic report of attitude. The GAD takes in the AHRS digital attitude information and converts it to an analog report the autopilot computer can understand. Maybe a tiny bit of the AHRS precision is lost in the translation to analog, but what I have seen in my airplane is improved autopilot performance in every way.
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How AHRS Works A spinning gyro remains rigid in space, resisting the forces of acceleration. So the attitude gyro is spinning about a vertical axis and remains vertical as the airplane pitches and rolls around the gyro. That little airplane symbol we see on the face of an attitude indicator is actually remaining stationary relative to the horizon while the airplane — the background of the instrument — moves. An AHRS uses tiny sensors to measure acceleration, and a fast computer chip analyzes those forces and calculates airplane attitude. By sensing acceleration in all axes, the AHRS can calculate how attitude has changed and thus determine the actual attitude of the airplane at any instant. A fundamental part of the calculation is also track over the ground. A remote flux detector measures the earth's magnetic field, and that magnetic information is applied to the track calculation to determine the compass heading we all see on the PFD. The complexity of the AHRS calculation and the necessary sensitivity of the sensors in the system are almost impossible for most of us to fully understand. And that such a precise device would be affordable to piston airplane owners is truly mind-boggling. The first AHRS - though we call it an inertial reference system — was developed by Honeywell and used laser beams to sense acceleration. The laser beams race around a small track reflecting off mirrors in each corner of the loop. Any acceleration deflects the laser beam, slightly changing the frequency of the received light at the end of the loop. The magnitude of the change in light frequency is proportional to the acceleration. The laser reference is still the gold standard for determining attitude, and the systems work wonderfully and last almost forever, but cost hundreds of thousands of dollars. What made the AHRS price breakthrough possible a few years ago was development of sensors for the automotive industry. The skid- and traction-control systems in a modern car also need very sensitive acceleration sensors, and it was the demand of the auto industry, and its huge volume, that drove down the cost of the essential electronics to help make AHRS available for airplanes of all categories. Some AHRS also use air pressure changes in the attitude calculation. A change in vertical speed or airspeed as measured by a digital air data computer can help stabilize and refine the attitude calculation, and these systems are called ADAHRS (air data attitude-heading reference systems). The AHRS used in the G600/500 is the Garmin GRS 77, which is part of the thousands of G1000 integrated glass-cockpit systems delivered over the past several years. It does not use air data in its calculation and can realign itself in flight, which is not necessarily true of all lower-cost AHRS. |
Great Glass
There are continued improvements in flat-glass technology driven mostly by the computer and consumer markets, and aviation rides along on that tide. That means the avionics system designed and certified most recently is going to have better flat glass than those designed earlier, and the G600 is a recent design, so the resolution, brightness and viewing angle of its display are as good as any at any price point, even for the big jets.
At first, I wondered about the usefulness of packaging the G600 PFD and MFD in a single 10-inch-wide case. After all, I had MFD information on the GNS 530 and 430 in my radio stack. Would the MFD in the G600 be that useful? The answer is an unqualified yes.
The MFD display in the G600 has more space than those in the radio stack do, so it can show more information. It also has a much more powerful computer processor, so it can deliver more weather, navigation, chart and other data than most other MFDs can. And I have found that looking at the MFD right in the center of the panel is significantly better than looking over at the radio stack is.
The MFD is divided into four sections for navigation, weather, auxiliary and flight-plan functions. In each of those sections are pages, most of which can be totally customized by the pilot. A long menu of options allows you to configure each page for what information you want to see and at what ranges. A declutter button allows quick removal of less important data when you want to focus on a Nexrad weather radar picture or a map of the approach, for example.
The MFD pages are not exclusive either. For example, you can see Nexrad returns on a nav map page, and see nav data on a weather page. You can select between plain background for the maps, or chart-style color-coded terrain.
