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12/4/2019 12:29 PM
 

Hello,

I have a Stratux box (ADS-B in) with iFLY GPS software on a Samsung tablet.  The other day I had a close encounter with another plane that came within about 1 mile of me at very nearly the same altitude - VMC conditions.  He was overtaking me, and I was on an IFR flight plan.  The app indicated zero (to slightly low) altitude delta and was showing red at my 6 o'clock. This caused me great concern so I called ATC, who indicated that the other plane was VFR and he was not talking to him. I climbed to move away from the other plane.

After the flight, I reviewed the ADS-B data which indicated that the other plane was actually at 5500, while I remained at 6000'.

Question: Why did the iFLY indicated zero altitude delta when the recorded ADS-B data indicated otherwise?  Why didn't I see the actual (GPS/ADS-B data) 500' delta indicated?

See attached Google Earth view.

Jeff

/Portals/0/Uploads/MPV%20Flight.jpg

 
 MPV Flight sm.jpg
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12/4/2019 5:38 PM
 

Hi Jeff,

There are several things that can cause altitude discrepancy.  Best guess, your Stratux/iFly is using GPS altitude, the ADSB Out from the other aircraft was pressure altitude.  There is a setting in iFly that attempts to compensate: Menu -> Setup -> Units of Measure -> Pressure Altitude Support.  If selected, iFly will use pressure altitude data.  Current Stratux builds have a pressure sensor, but it won't work in a pressurized cabin.  Some ADSB in/out units send pressure info that comes straight from the transponder (Echo and SkyGuard are 2 examples)...but the Echo is very problematic for some reason.  Anyway, iFly can use this raw pressure data and combine that with the altimeter setting from the nearest metar to get a good pressure altitide.  

-Walter

 
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12/4/2019 6:04 PM
 

Thanks for the feedback. I'll take a look at that function. 

Jeff

 
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12/9/2019 9:10 PM
 
  Some ADSB in/out units send pressure info that comes straight from the transponder (Echo and SkyGuard are 2 examples)...but the Echo is very problematic for some reason. 

-Walter

Would you explain a bit more reguarding the problems seen with the Echo. I have one and it seems to be operating well and integrating with the 740b fine, but I have not been looking for problems either. It did take some tuning of the sensitivity level to pass the ADSB flight testing, but no problems since then and no complaints from ATC. I was not aware of the iFly pressure altitude option and may give that a try.

Best,

John

 
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12/9/2019 10:02 PM
 

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.


Walter Boyd
President, Adventure Pilot
 
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HomeHomeDiscussionsDiscussionsiFly Owners Q&AiFly Owners Q&ADelta Altitude Depiction IssueDelta Altitude Depiction Issue