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12/10/2019 11:03 AM
 

Walter, thanks for the response. That explanation reguarding the Echo sounds resonable. I have been blanked out from radar when flying lower in the Appalachian foothills and notified by ATC that they were losing my contact. I'm assuming this is not a problem if you are not changing altitudes and the Echo is reporting your last interrogated pressure altitude from the transponder. I actually did have the Pressure Altitude function turned on - just didn't remember setting that up!

John

 
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12/10/2019 2:42 PM
 
Walter wrote:

We've had a few customers report inacurate altitudes, random "terrain alerts" mid flight, and dramatic changes to rate of climb.  We've traced this back to the pressure altitude coming from the Echo.  It doesn't affect everyone, but it has some.  I recently heard something that may explain this: The Echo is passively getting pressure altitude from the transponder, but a transponder doesn't always transmit, it waits for a radar ping, then it replies.  So if you are in the middle of nowhere it might be a while between sweeps, so a change of altitude wouldn't be registered for a while.

Thanks, Walter. I hadn't thought about the need for a ping to get the Echo to report altitude. I had a different condition a few days ago, when in a flight of two Seareys, flying at about 100 feet above the James River in VA. The other guy could see me on his EFIS (not an iFly) but I couldn't see him. I did, however, see other traffic about 1,100 feet higher and more.

Flght Aware usually tracks me when I'm above 1,500 or 2,000 feet, and occasionally even when I'm on the ground. FlightRadar24 almost never spots me at all. A uAvionix tech told me that's because they look for 1090 mHz transmissions, but the Echo only transmits on 978. So they see 978 mHz traffic only when the signal is re-transmitted by a 1090 setup.

 
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12/19/2019 8:09 PM
 

Don and all,

An interesting aside reguarding FlightAware that I ran across a few weeks ago. I was flying from AHN to MDQ VFR with flight following when the rest of my airport buddies were at our usual Friday lunch BBQ Shack. They decided to check on my progress during lunch with FlightAware. When they pulled my flight up it appeared that I was having great dificulty maintaining altutide. It was a little turbulent and I was busy chaging freq and responding to ATC across five sectors north of ATL while looking for traffic, but I was usually within 100 feet of my declared altitude. What they were seeing was altitude excursions of 100s of feet. The ribbing I upon my return was considerable until I pulled up the data to look for myself and showed them an interesting correlation. My reported altitude was correct anytime the data came from ATL Center or TRACON sources but was consistantly 300 - 400 feet low when the source was a FlightAware ADSB Station. Don't know what the FlighAware station data problem is, and I doubt it affects what ATC is seeing since ATC never questioned my altitude, but it apparently does show up in the FlightAware system. BTW, the iFly 740b is such a pleasure to fly with! Seeing traffic displayed enroute through the busy north ATL airspace is a great help as is picking up the current Wx at the destination when still out of radio range. I've attached a portion of the FlightAware data to show what I found.

Fly Safe,

John

 
 AHN-MDQ FlightAware Errors.JPG
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12/20/2019 8:54 AM
 

ATC receives your pressure altitude from your transponder, which does not include a Kollsman correction, and will apply a Kollsman correction at the controller's console.

Flightaware may not be applying the Kollsman correction.

 
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