XM vs ADS-B

[Lenny Iszak]

I have both in my plane. One screen displays XM the other ADSB.

XM has base reflectivity and composite radar while ADSB has composite only, and composite almost always looks worse.

XM also has lightning data, cloud tops, satellite images, ADSB doesn't.

XM works in mountains and on the ground ADSB doesn't.

They both take time to update, but when cutting it close (not that i would ever...) and watching the weather move you get updates more often than you would from a single source.

ADSB has a cool feature that I haven't seen implemented yet: Special Use Airspace status. Is any software displaying that data on their map?

Foreflight has a good comparison of XM and ADSB: https://www.foreflight.com/support/xmvfisb/

At low altitudes I also use RadarScope on my iPhone, it updates faster, it's more accurate (super-res radar), and you can select any radar tilt you want, it even has live precipitation and wind data.

[Bluelabel]

Good info, thanks,
Does anyone know if, say you had a G3X with XM or the GDL51R, can you use the music side of it without the weather?

[Carl Froehlich]

Originally Posted by Bluelabel

Is it worth it?
Is there anyone that has flown with both? Preferably with the G3X system since that's what I have. SNIP

I was an early ADS-B in/out guy in the RV-10 (dual 10" SkyView setup with Dynon ADS-B receiver). I did not have faith in the ADS-B weather so I ran XM weather side by side with the SkyView system for the first long cross country to Key West. As is normal for Florida, we had massive thunderstorms to fly around. The SkyView ADS-B weather was identical to the XM, and in no case did the SkyView not update at least as often as the XM.

After returning home the XM receiver was removed from the plane and the overpriced XM subscription cancelled. I have several years flying with the SkyView ADS-B data and have always been ahead of the controllers on weather and contacts. Of late I've been flying an RV-8 that does not have ADS-B and have used an iPad running ForeFlight and a Bluetooth connected ADS-B in receiver. While this works, I hate it. With the SkyView the data is always displayed. With the iPad you have to think about looking and just when you really want data the iPad picks that point to overheat and shut off. While the iPad is a good backup, I recommend it not be used as a primary ADS-B display.

Carl

[Dan Langhout]

Originally Posted by Bluelabel

. . . . . Does anyone know if, say you had a G3X with XM or the GDL51R, can you use the music side of it without the weather?

I do this now on my GDU-375 G3X display - don't know about the GDL51R. Used to have the XM weather as well, but dropped it when I went to ADSB using the GDL-39R.

[Robert Anglin]

This year our little 8 went to KOSH and had to face a lot of weather, headed down to the south east on Thursday to get home. The refresh rate was about every five minutes and was very correct all the way home for some 575 Nm.
The square blocking look to it we found was not a hold back. You just got used to it and it did paint everything with the correct coloring for what we had to work around, through and in. If it were not for the G3X "GDU-460" we should have stopped in Frankford Ky. for the evening, but we could see that we would be able to go do south down to Knoxville and then get behind a long line that was across our path. We then worked around the south edge of that line watching the weather most of the way for another 150 miles or so. We found it to be fully useful and up to the task. Hope this helps, Yours, R.E.A. III #80888

[BobTurner]

I hope everyone remembers that the refresh rate, and the update time shown on the screen, are not the true total delay. Whether xm or ADSB, they have to wait for all the radars to sweep, and for the NWS computers to put it all together, and send it out. While usually just a few minutes the actual delay is unknown to the pilot. This data is great for strategic avoidance. It was never meant for close in maneuvering.

[vic syracuse]

Originally Posted by BobTurner

I hope everyone remembers that the refresh rate, and the update time shown on the screen, are not the true total delay. Whether xm or ADSB, they have to wait for all the radars to sweep, and for the NWS computers to put it all together, and send it out. While usually just a few minutes the actual delay is unknown to the pilot. This data is great for strategic avoidance. It was never meant for close in maneuvering.

Very well said. These tools are for strategic weather avoidance, and should never be used around fast-moving fronts for penetration. The delay is just too great. Using them in far enough ahead during the trip usually means heading changes of only 5-10 degrees along the route.

Except in the Southeast in the summer time with the thunderstorms. The T-storms tend to stay put as they are not associated with fronts. You really can use it to circumnavigate the big ones, giving them a wide margin. I fly trips from Atlanta to Florida now that I would never have done just a decade ago. However, I never file IFR when there are T-storms along the route. I always use flight following and its a lot easier to make heading and altitude changes without waiting to request it from ATC. Usually the frequency is the busiest right when you need to make a request. I've learned to tell ATC that I'll be up and down, sometimes 4K'-5K' with some heading changes. They can usually see what you are looking at as well, and it works out well. I also like to see that the view out the window is matching the picture depicted on the screen. If it's not matching close enough, I make the appropriate routing changes.

Back in the late 70's before we had all of this on-board weather equipment, I was inadvertently left to fly into a really big cell while IMC over the Gulf of Mexico. I don't ever care to see the inside of a cell again.

Vic

[JPalese]

Originally Posted by BobTurner

I hope everyone remembers that the refresh rate, and the update time shown on the screen, are not the true total delay. Whether xm or ADSB, they have to wait for all the radars to sweep, and for the NWS computers to put it all together, and send it out. While usually just a few minutes the actual delay is unknown to the pilot. This data is great for strategic avoidance. It was never meant for close in maneuvering.

I want to echo and underscore what Bob said about both of these products -- they are designed for strategic planning, not tactical maneuvering.

There have been fatal accidents that resulted from folks using ADS-B or XM radar data as if it were weather radar to try and navigate through severe weather.

Both products are great and both have the same limitation - what you see is what has already happened - it is NOT a CURRENT or LIVE picture of the weather - merely a picture of where the weather was at a certain PAST point in time.

Generally speaking the information on "how old" the data is indicates how long ago it was transmit, not when the data was actually recorded.

There can sometimes be up to a 30 minute delay from data collection to actual transmission.