My GPS source is not the iPad, it’s an SBAS augmented GPS on the SkyEcho 2. Also, using a brain and knowing your airport’s elevation + having an idea about the terrain around it + using your altimeter in the airplane, is a good idea.
Having said that, I’m. not. going. to. try. it. And nobody should actually fly an ILS approach using a Yaesu 750 either. But hey, I’m just trying to answer the original question posted by Peter.
Dimme wrote:
The GS goes away at 800 feet GPS altitude
It is actually 500 ft AAL, which figures as ESME has an elevation of 296 ft.
Peter wrote:
why doesn’t someone do LPV?
There you go! Accepts Jeppesen database
Not quite a handheld but one could easily make a casing with 3d printer and mount it like an Ipad.
Given that the aim of the exercise is to land an aircraft with a handheld device to CAT 1 limits it would seem that breaking the rules and using untested high tech equipment seems to have blinded some to the legal option.
The first thing to do to is to get an external antenna connected to your hand held VHF radio ( you can expect the range to go from 7-10 miles using the rubber antenna to 50 miles + with the external antenna ). Next make sure you have your headset connected to the VHF radio.
Most military airfields have Precision Approach Radar, declaration of an emergency will open up the military airfields to you and the PAR will give you the ability to fly to CAT 1 staying legal and to touchdown in practical terms.
The minimum equipment needed is the VHF radio, altimeter & turn coordinator.
Peter wrote:
It may not actually be illegal.
It certainly is in the US. However, in an emergency, anything goes of course. A_C’s idea about a PAR approach is a good one. Depending where you fly, there’s mostly a mil field not too far away (certainly the case here in CA !).
A_and_C wrote:
The minimum equipment needed is the VHF radio, altimeter & turn coordinator.
If the handheld VHF and GPS work while everything is off, I will give the Mil PAR a go, usually their runways are long enough to go easy
No way one would just go there NORDO and ATC are rarely around on weekends 
Back to the OP, in this “unlikely scenario” anything with lot of precision and too much airspace/terrain/procedure complexity and RT distraction is really bad
Assuming an emergency, the sensible and practical option is a long 3km coastal airfields (even with no CAT1/CAT3 glide slopes), just “SkyDemon/GTN VFR guidance” to 500ft/2nm from threshold
Then one would just fly fixed ASI+ROD bellow 500ft agl down to ground while counting his watch time, say 120kts at 400fpm
My guess it has to in one go and hope runway is long enough: no go-around from bellow 500ft outside a clear LOC/GS signal
IMO first priority is to fly: that means stable ASI+ROD bellow 500ft not trying clever navigation around sluggish NAV signal
Altough far more easier to just fly wing level find VMC and land (with enough fuel anyone can make south of Spain)
PAR does exist at some military airports, but many military airports in the US don’t have PAR, so the nearest might easily be several flight hours away. I would opt for a battery backed up system or a standby alternator. In a dire emergency, an iPad/flight bag would have to do.
Very few UK airports have PAR. The chance of a GA piston pilot being within range of one is miniscule. I recall once flying a PAR into Newquay EGHQ (the RAF is long gone there) and their radio was so poor I could barely make out the ATCO’s voice… that was a well known thing with RAF stations back then (they bought some crappy radio kit). PAR also requires a lot of practice; it is no easier than an ILS, IMHO.
That GRT product, mentioned by @RV14TDbuilder, is interesting. It states Our US navigation database now includes IFR approaches within it for most GPS, ILS, and VOR approaches. Soon Jeppesen databases will support IFR approach and may also be purchased. In the past, it appeared (but was never proven) that Jeppesen would refuse to sell their IAP data to anyone making an uncertified navigator GPS. It was assumed that this was due to liability. So I would be quite surprised if they do offer even just the display of the Jepp terminal charts let alone LPV capability. However, anyone can make a navigator which is windows based and can run Jeppview, so Jepp wouldn’t need to know anything about that, and LPV capability is no more than implementing the “hex block” which for each airport is published in the AIP. And Jepp appear to want to abandon the PC/windows platform…
From memory I seem to recall that LPV has several requirements:
1. SBAS (WAAS, EGNOS, …) to be available and working – no RAIM issues. Is your iPad SBAS-aware or do you need an external GPS thingy? (Honestly don’t know.)
2. A panel-mounted GPS with proper annunciators and a few more requirements.
Because of the second requirement, even if you could get LPV working on a proper SBAS-enabled handheld device, I don’t think Jeppesen and the like are going to sell you their database.
My old Garmin GPS III from the beginning had CDI with glidepath needle that disappeared 500 ft above the waypoint elevation. I made a spreadsheet with runways, their elevation, (M)DA and final approach glideslope angle, and from that calculated the waypoint offset (NM before/after reference point) and a phantom runway elevation. By entering those values into the GPS III, the HSI would take me down the chosen glideslope, with the glide indication disappearing just as the (M)DH was reached. In effect, an LPV with built-in (M)DH alert. It did work, but as the GPS III was an early-gen GNSS and without SBAS, it was not accurate enough to comfortably go much below 500 ft anyway.
I do not think the trick is possible on newer GPS’s as airfield elevations cannot be modified by the user. But I use SkyDemon as in @Dimme’s picture above, and it works fine down to 500 ft.
