The place for technical discussions about GA and flying.
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User avatar
By flyer5
#1891419
The ILS display on SkyDemon cuts off at 500 feet.

I seem to recall someone I didn't know showing me an app on his phone which provided guidance down to zero feet. I've had a rummage around since then but app stores are like the Wild West and I've not had any luck.

Do you use any GPS apps that provide guidance throughout the approach?
User avatar
By AndyR
FLYER Club Member  FLYER Club Member
#1891455
Not sure I’d trust any mobile device for an accurate enough GPS ILS indication.

Obviously fine for VFR guidance but why would anyone need that below 500’?
Last edited by AndyR on Mon Jan 03, 2022 10:57 pm, edited 1 time in total.
User avatar
By Rob P
FLYER Club Member  FLYER Club Member
#1891456
Timothy, a hugely experienced CPL, wrote off his aeroplane on a landing.

This might inform your opinion of the efficacy of this app.

Rob P
By riverrock
FLYER Club Member  FLYER Club Member
#1891461
I don't remember his write off to have anything to do with an app?

With Sky Demon they haven't coded the touch down point, so for runways with a real ILS you are aiming at a different point ( piano keys).
Doesn't matter much when you are at 500 feet though.

I wouldn't trust an app for vertical guidance.
The use of phone location services as GPS means updates approx once per second ( rather than continuous) so you will travel 40 meters before your next update. Height accuracy will depend on how good the signal is received from many satellites, atmospheric conditions ( no EGNOS to provide corrections), which goid and correction factors are in use ( and whether it matches the one in the app), prediction algorithm within the device ( for an illusion of smooth updates, it guesses where you are between measurements).

Some apps may interrogate the onboard or external satellite recievers directly for more accurate results, but you are trusting in the app coding even more.

They are good for training aids in VMC but not too be used "for real".
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User avatar
By Paul_Sengupta
FLYER Club Member  FLYER Club Member
#1891464
Rob P wrote:Timothy, a hugely experienced CPL, wrote off his aeroplane on a landing.


Doing a standard instrument approach and not stopping in time on the runway due to a bit of a tailwind.

Rob P wrote:This might inform your opinion of the efficacy of this app.


Indeed it might. He said if he'd used his first instincts to use it to come in from the other end that accident probably wouldn't have happened.

However...

riverrock wrote:I wouldn't trust an app for vertical guidance.
:
no EGNOS to provide corrections, which goid and correction factors are in use ( and whether it matches the one in the app)


This. I haven't come across many phones or tablets which do EGNOS. And even if they did you'd need a clear view of the sky to the south and have some sort of flag to say it was being used...which isn't coded into the GPSILS app.

Using my EGNOS enabled GPS in my PilotAware for Sky Demon, my altimeter and GPS altitude on the tablet are usually within 20ft of each other. I can't say the same for the GPSILS app relying on the tablet's internal (non EGNOS) GPS.
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By Dave A
#1894387
Unfortunately, the developer of the GPS ILS Android app discontinued it in 2015 when it stopped working properly on later versions of Android.

A shame, as, once you'd told it where you wanted to touchdown on any particular runway (which you could double-check with Google Maps), it would bring you down to exactly that spot. I never used it in anger, but my trials showed it had unerring accuracy.

Never found anything similar to replace it.
User avatar
By flyer5
#1894975
It's arguably too much.

The magenta line gives you all you need to fly, and approach in VMC. So what's the ILS for? The notion you use it for some sort of practice, is somewhat implausible.

Most of us are not allowed to fly in IMC and none of us is allowed to make an instrument approach using SkyDemon on a tablet.

Once you accept that, then your views on GPS ILS are more complex. I've never used SkyDemon for IMC approaches but I would imagine that in general it is superior to non-precision methods. 'In general' is an important caveat but nevertheless, if a capability is possible, why not have it as an option?
User avatar
By Paul_Sengupta
FLYER Club Member  FLYER Club Member
#1894978
flyer5 wrote:It's arguably too much.


It's free!

flyer5 wrote:The notion you use it for some sort of practice, is somewhat implausible.


Why's that?
User avatar
By GrahamB
FLYER Club Member  FLYER Club Member
#1895019
flyer5 wrote: .. and none of us is allowed to make an instrument approach using SkyDemon on a tablet.

Would you like to post the regulation that specifically prohibits that?
User avatar
By flyer5
#1895032
To use ‘RNP approaches’ aircraft need to
have a suitable IFR approved GNSS set-up
installed. The equipment must also contain
an up-to-date navigation database with
details for the required ‘RNP approach
procedure’ to an airfield. When activated,
the aircraft navigation equipment
automatically sequences through the
procedure’s legs to bring the aircraft to
the runway.
There must also be an On Board
Performance and Alerting system to warn
the pilot of positioning errors, loss of
signal, degraded tracking accuracy and
other parameters.


From https://publicapps.caa.co.uk/docs/33/EGNOS_V4.pdf
User avatar
By GrahamB
FLYER Club Member  FLYER Club Member
#1895033
flyer5 wrote:
To use ‘RNP approaches’ aircraft need to
have a suitable IFR approved GNSS set-up
installed. The equipment must also contain
an up-to-date navigation database with
details for the required ‘RNP approach
procedure’ to an airfield. When activated,
the aircraft navigation equipment
automatically sequences through the
procedure’s legs to bring the aircraft to
the runway.
There must also be an On Board
Performance and Alerting system to warn
the pilot of positioning errors, loss of
signal, degraded tracking accuracy and
other parameters.


From https://publicapps.caa.co.uk/docs/33/EGNOS_V4.pdf


That's not a regulation, that's a magazine article, notable that it doesn't reference a regulation either.

To be fair, I'm playing Devil's Advocate here! There are all sorts of approvals required for equipment and installations used for RNP approaches, and I'm not advocating rocking up and flying an approach on less than certified equipment. However, the law is strangely silent on making up your own approaches, so making one up that closely follows a surveyed and properly designed track and profile is probably safer than one to your home strip in the back of beyond.