My analysis turned out to be correct. The red Nexrad returns contained heavy rain mixed with big wet snowflakes. There was occasionally moderate turbulence, but none of the up- and downdrafts of convective weather. By the time we got to Savannah we were flying in light rain between layers on top of a low overcast and were number eight for the ILS approach. I spoke with a couple of light airplane pilots after landing who all wanted to continue north but stopped in Savannah because of what they and weather briefers saw on the radar, and because of forecasts of ice. There was no ice, and the precip was nothing but wet. I don't blame them for being cautious because it did look bad to anybody with a radar picture.
So, for the many in aviation who believe that Nexrad and other current weather data in the cockpit are going to answer all go, no-go questions for pilots, they're wrong. If you avoid all Nexrad returns you won't get wet, but you will also delay or cancel many IFR trips that are no threat to a competent instrument pilot. It is still necessary to consider the overall weather picture to fly in and around precipitation while still avoiding thunderstorms.
I am probably the only pilot with both the Avidyne EX500 and Garmin GDL 49 datalink systems in the same airplane. It makes no sense to have both because they can report much of the same information, but it is a test to compare the two because both use the same low earth orbit constellation of satellites.
The Avidyne EX500 is fairly new, while the Garmin system has been available for a few years. The Garmin GDL 49 is a remote satellite transceiver that is controlled by a GNS 430 or 530, which also displays the weather data. The EX500 is a self-contained multifunction display that shows moving maps, terrain and, if you have it, airborne weather radar, as well as satellite linked weather information. To use the Garmin system you request specific weather information, such as the Nexrad image and metars. The Avidyne system uses a technique the company calls narrowcasting to automatically retrieve Nexrad and other weather data along your route of flight, which the EX500 knows from the flight plan you have entered into your GPS navigation system.
As soon as you power it up, the EX500 begins automatically requesting and receiving weather data for your route. It will receive full text metars for airports along the route, little colored flags that show weather as VFR, marginal VFR, IFR and so on for each reporting station, and also diagrams airmets and sigmets over the moving map. Avidyne also receives and displays the location of temporary flight restrictions (TFRs) on the moving map, but the FAA's reporting of those restrictions is not reliably timely, so Avidyne cautions that the TFRs shown on the EX500 may not be complete.
I like the automatic operation of the Avidyne system and find the graphical display of airmets and sigmets over the moving map to be very useful compared to a text definition of the boundaries of affected area. The EX500 also does a wonderful job of operating and displaying returns from my airborne weather radar. The radar is an older Bendix RDR 160, which has been a popular and reliable radar, but the EX500 transforms the raw data from the radar into a picture with superb resolution.
When I first started flying with the GDL 49, and now the EX500, I worried that the 10 or 20 minutes that may have passed since the Nexrad mosaic was assembled on the ground would diminish the value of the image in the cockpit. But I haven't found that to be a problem. The Nexrad radar picture gives you the information to make major course deviations to avoid weather, or to analyze it and fly through it, as I did on the trip down the coast. Even fast-moving storms don't change position that much in 10 or 20 minutes, so the "latency" issue of the image just isn't a factor. If you're trying to determine if a storm is on the localizer, or a few miles to either side, these systems can't do it. You need your own radar in the nose for that kind of real-time weather information, and even with that data, you probably want to avoid a thunderstorm by more than a few miles.
However, before you buy either the Avidyne EX500 or Garmin GDL 49, you need to know that there are periods when you won't receive any data. I have seen as much as an hour go by without receiving a new Nexrad image, or any other fresh data. These reception outages are completely unpredictable, and I haven't been able to find any common pattern, such as flying in a cloud, that could cause precipitation static, certain altitudes or routes.
Avidyne and Garmin are both trying to develop new software that improves reception, but nobody knows for sure what causes the problem. My theory is that even though a satellite in the constellation is in view 99 percent of the time, the geometry between the positions of the antenna on the airplane and the satellite is poor. I believe this because both systems suffer signal loss at the same time. I have never seen the EX500 or GDL 49 work well when the other didn't. The only common link is that both are using the same satellite network.
I hope that the reception problems can be overcome because the fundamental technology and performance are so helpful. You can receive the signals at any altitude, even on the ground before takeoff. The Avidyne EX500 usually has a Nexrad image and most metars for my route before I take off. The EX500 also delivers a great deal of capability for the money. The big screen multifunction display, including the satellite transceiver, costs $8,885. For that you get an excellent moving map, a terrain depiction including obstacles, and data other than weather, such as TFRs. The EX500 with airborne weather radar capability costs $9,995 for basic radars like mine up to $14,995 for the most complex big airplane systems, and it replaces your weather radar display with an improved image, plus all of the other satellite and map data.
Buy the EX500 with the knowledge that you will get one of the best values in a multifunction display all of the time, and get Nexrad and other weather data 85 to 90 percent of the time. But there will be periods when satellite reception won't be possible, and at this time there is no fix for that. And no matter what, believe Richard Collins. You do need to understand the big weather picture to put the new cockpit weather data we have available to optimum use.