Primarily for general aviation discussion, but other aviation topics are also welcome.
By Mr Dinos
#1852647
Hello,

I was wondering if anyone has experienced a similar issue to one that I’m currently struggling with and is only a recent phenomenon in the last few months but cannot put my finger on what might be causing it.

Device is an iPad Mini 5 cellular with built in GPS running the latest IOS running the latest version of SkyDemon.

In summary immediately after takeoff and close to the ground I get very erratic GPS performance which can be seen in the following Skydemon track log. From the track log the altitude is bouncing around quite a bit and the location is equally erratic and a little bit off. It behaves this way when closer to the ground but as I climb it sorts itself out and becomes more accurate.

It’s something I’ve never seen previously and cannot put my finger on what’s happening.

I’ve since purchased a Garmin Glo but haven’t had a chance to test it out. It seems to be confined to my home airfield Elstree and in my specific aircraft, a C172. I’ve tried moving the location of the iPad from lap to yoke with the same result.

Is this something anyone else has experienced and if so am I missing something obvious?

Would appreciate any thoughts


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By Flyin'Dutch'
FLYER Club Member  FLYER Club Member
#1852651
1.I know nothing
2. If I had to guess - could it have to do with the iPad trying to locate itself close to the ground by mobile phone masts and that this is no longer possible above the 1500ft where the track recording gets less erratic?
By Mr Dinos
#1852652
Thanks @Flyin'Dutch'

That had crossed my mind that it could be the proximity to Mobile phone masts are allowing (forcing?) those to be used in preference to more accurate GPS location. I was going to experiment on my next flight by turning off mobile data (and wifi) and seeing if that makes a difference.

I guess my question is if that’s the case why would that be happening.
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By Mr Dinos
#1852672
That’s what I thought but then I came across this statement on an apple support article and wonder if there’s more to it.

“Location Services uses GPS and Bluetooth (where they're available), along with crowd-sourced Wi-Fi hotspots and cellular towers to determine the approximate location of your device”

This is almost suggesting it uses these sources continuously where available rather than just initially.
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By johnm
FLYER Club Member  FLYER Club Member
#1852690
I run a iPad which uses SE2 or its own GPS and has a SIM which provides mobile connection unless I put it in airplane mode which I often do to stop headset noise or if flying at FL100. Never had a problem.

The only phone we ever actually chucked was a Samsung running Android
By Mr Dinos
#1852691
To be fair this is only a recent issue. I’ve been using various iterations of iPad running Skydemon for many years and have always been rock solid and no different than either panel mounted Garmin or my trusty Garmin gpsmap 296 in both reliability and accuracy.

That’s what’s making this all the more frustrating!
By Lefty
FLYER Club Member  FLYER Club Member
#1852702
1. If it only occurs on take off from Elstree then I strongly suspect that there might be somebody or something that is jamming / interfering with the GPS signal.(whether intentionally or not). If the source was in your aircraft it wouldn’t correct itself shortly after takeoff.

2.The more expensive / dedicated aviation GPS’s (eg the Garmin h/helds and installed units) download and store a database of the orbits of all the GPS satellites which it uses to predict which satellites will be visible (usable) when it is switched on. This database is known as the “Almanac”. The satellites that will be visible changes by the time - and your location on the planet, so if you were to switch on your Garmin GPS more than approx 200nm from where it was last used, it can take 15-20 minutes to download the Almanac and establish its position.

3. To avoid having to spend 15 minutes downloading the Almanac, consumer GPS’s (eg phones and tablets) use nearby cell towers and wifi signals to find their (approximate) position which then allows the device to know which GPS satellites should be usable. Once it has locked onto the appropriate GPS satellites, it continues using the GPS satellites for it’s accurate navigation. For this reason, it is a good idea to ensure that your phone / tablet is switched on in the clubhouse for a couple of minutes before you go flying, to allow your phone to find its approximate location.
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By GAFlyer4Fun
#1852708
I have an ipad mini 2 cellular and that gives an SD position so much quicker than the panel mount even though the panel mount gps status screen shows it has several satellites to give it a good position.
Thats with the aircraft in exactly the same position as the panel mount gps was turned off a few hours earlier.

I suppose certified kit has to go through a few more hoops.... that is not just admin.