You could just forget about quaint old QFE like everyone else in the world does

Amen, Biggles.

One of the first things that we do as pilots when preparing to take off is set the altimeter to the regional QNH to display altitude and one of the last changes that we make to the altimeter as we approach the field is to set it to the runway threshold QFE to display height.

So why not have a feature in SD which allows for the same operations in order to correct any inaccuracies in the GPS acquired altitude as displayed on the moving map screen and any derived calculations that SD makes.

A "slider" (knob or something) on the side of the map which allows me to "adjust" the displayed altitude to that as shown on the cockpit altimeter would resolve the problem and improve the accuracy of any subsequent height based calculations such as the virtual radar, RoD and glide slope display on the ILS.

I have to say that the difference between the GPS SD displayed altitude & the cockpit altimeter has been, in my experience, very little and I have been really pleased with the accuracy of the iPad derived GPS data however I do accept that this is solely dependent on the visible number and orbital position of the GPS satellites.

Having said this it goes without saying that the primary source for altitude/height remains the cockpit altimeter.

One final thought that needs clarification which sprucegoose's post correctly identifies. The QFE measures height above the airport's chosen runway however, as far as I can make out, the height as indicated by SD uses terrain clearance at the current GPS coordinates, whereas the altitude readout gives AMSL, which means I would never use SD's height option when approaching an airport. I stick to the altitude option on the display otherwise sprucegoose's noted QFE/height inaccuracies will always be present and the height information unreliable at any given point if you treat it as the QFE readout while carrying out an approach.

Biggles -- EGKB

On my iPAD3 the GS is always 1/2 scale deflection down when on the Glide Slope. Surprisingly, my Chinese GPS navigator is as accurate as the actual ILS needles (bearing in mind the hide & seek factor of the GS needle in SD). However, all that is beside the point. The real point is that here all is not at the pilot's disposal. Having some approximate information is better than having zilch & a psudo ILS that does not play hide and seek would not make flying too risky. Hiding it would not enhance safety.

Very Newbytheway

DurhamTeaseAirport

On my iPad 3 the gps derived height is around 200' below the QFE, and the SD glideslope is on the bottom of the scale when I'm actually on slope. So I'm not about to rely on a £600 iPad to keep me alive any time soon, and even as backup I think I'd have to have a WAAS gps addon before I even went to 600'

More relevant information, is a prerequisite to better decisions. ROD and AC position constantly vary in flight. Now would it be better to avail such info to the pilot or do we feel that it would be unsafe to do so? I certainly would have appreciated even approximate info when both my suction pump and air speed indicator packed up on take off. Something is better than nothing I'd say.

Very Newbytheway

DurhamTeaseAirport

I realise that SD is a VFR flight software application but "information is everything when flying, redundancy is reasuring and I'm looking out the window as you suggest and and and ......."

White fluffy things, 100% coverage -- currently @ 1200ft QFE with DH of 600ft and required RoD uncertain but cockpit GS indicates I'm high which is confirmed by SD's GS display; I'll guess at about 450-600ft/min (give or take a few hedges).

......and and and, let's look on the bright side, the guys in the tower might quite like another hedge cutting

Biggles -- EGKB

Ummm, I think I'd rather you just looked out of the window to be honest...

Multiple airspeed by 5 and that gives me my RoD for a 3.5 deg glide slope - yes I remember that from my PPL training days. That's great if the aircraft is properly established on final and the aircraft remains in this ideal world but if SD's GS indicates that I am too high at 2nm with a ground speed of 80kts multiplying by 5 has a tendency to land me on the upwind numbers on a medium length runway (leaving me heavy on the brakes and no rubber on the tyres) and in the hedge on a short runway (leaving the airfield with no hedge and me a very expensive lawn mower)

Now with a constant display graphically (which SD already gives via the GS) and the possibility of displaying digitally the actual RoD required to achieve the landing point (just an idea at the moment), serves to improve my chances of landing on the downwind numbers which the nice people in the tower suggested might be a good idea next time I give it a go!

Also, thinking back to my PPL training days I never could quite understand the "rule of thumb" of multiplying the airspeed by 5 (it doesn't work) as you quite rightly state it is your ground speed that's important in working out the RoD not your airspeed and what is the one thing that the standard 6 pack instrument cockpit display doesn't give you that a GPS device like SD does -- yes, you've got it GROUNDSPEED.

Now where did I put my Pooleys?



Biggles -- EGKB

Biggles-EGKB, iPlease permit me to iAgree with you once more.