It's been a tough year for business jet makers with few new orders coming in and cancellations diluting previously large backlogs, but demand for the light jet Citation Mustang is holding up better than for other models. And now that deliveries of Mustangs with Garmin's synthetic vision technology (SVT) are underway there is one more reason to want Cessna's entry-level jet.
The Mustang has logged a number of firsts. It was the first of the current crop of new light jets to receive full and unlimited certification. Approval in Europe quickly followed and deliveries of Mustangs to dozens of countries is underway. And now Mustang pilots can see the virtual picture of the terrain ahead on the G1000 system thanks to Garmin's SVT.
Since day one the Mustang has had the big Garmin 10.4-inch primary flight displays (PFD) in front of each pilot position, plus an even bigger 15-inch multifunction display (MFD) in the center. Flat-glass displays of such size and capability exceeded what was available in many midsize and larger jets, and was unheard of in a light jet before the Mustang. With the large and sharp flat-panel displays already in the cockpit, and a powerful central flight management computer driving the integrated system, the stage was set for Garmin to create the virtual view of SVT.
The synthetic view of terrain, obstructions and runways ahead of the Mustang is the result of a detailed database of terrain features that was originally created to warn pilots of a possible collision with terrain or an obstruction. That function -- generally called terrain awareness, or ground proximity warning system -- is, of course, still part of the Mustang's avionics system. But as the computers became faster, and the database ever more detailed, the people at Garmin realized they could create a virtual picture of the terrain ahead in addition to merely warning that a pilot was flying too close.
Garmin was not first to certify synthetic vision, but its timing was good because the technology allows a much more detailed and useful image than was possible even a few years ago. And Garmin also has the advantage of building the entire G1000 avionics system as an integrated package so there are no compromises when various elements of the system work together, as they must, to present a complete picture.
But generating the image of the world ahead of the Mustang is not the most demanding aspect of synthetic vision. The real challenge is to calculate the airplane's flight path and display it accurately. To me this is the most impressive aspect of Garmin's system because it would not have been possible even a few years ago at a price and physical size and weight that would suit a light jet such as the Mustang.
The key elements that make Garmin's flight path calculation possible are the precision of WAAS-enhanced GPS and the microelectronic gyros that are the heart of the dual attitude-heading reference systems (AHRS). These tiny and relatively low-cost nonmoving gyros calculate both the attitude of the airplane and its path through the air. As all pilots know, or quickly learn, airplanes do not necessarily go where they are pointed. Any wind will alter the flight path over the ground so heading will not exactly match ground track. And acceleration determines whether the airplane is going up or down no matter which way the nose is pointed.
The result of this flight path calculation is a circular symbol on the PFD that has tiny wings and a vertical tail. This symbol represents where the airplane is actually going, referenced to the earth beneath, based on the instantaneous inertial calculations provided by the AHRS sensors. If the flight path symbol is below an obstruction ahead, you will hit it unless you do something to change the path. The same is true for lateral displacement. If the flight path symbol is on the runway you will get there, no matter where the nose is pointed.
The flight path is what every pilot wants and needs to know, but until very recently we each had to calculate that path in our heads. By observing drift over the ground in visual conditions, or combining the information from a variety of instruments when flying in the clouds, we can come up with a reasonable calculation of flight path. But what a demand on available brain power that takes. It is so much more useful for the human to be able to spend his time in the cockpit thinking about the overall situation than concentrating almost totally on the minutia of continuously interpolating the readings of several instruments to estimate where the airplane is going. Garmin's flight path calculation and display does what computers do best and leaves what computers can't do to the human pilot.
The other essential element of synthetic vision is WAAS GPS navigation. The flight path computer is showing how you are progressing relative to the earth beneath, but it is the WAAS GPS solution that shows you exactly where you are and what's down there. The amazing precision of WAAS GPS locates the Mustang exactly over the spot on the earth below, and also shows the terrain ahead just as it is. With flight path only you would know that you are going left or right, or up or down relative to the ground, but WAAS GPS with its near perfect position fix allows you to see exactly what is down there, and out ahead.
