GPS Failure on Approach?

[colohan]

I am currently pursuing my instrument rating.

I was out flying with a much-more-experienced pilot friend of mine last week, and we were doing the VOR DME RNAV/GPS-A approach into KTRK using a GPS. Around the FAF the GPS glitched (lost all satellites for a few seconds), and this got me thinking...

In this approach you are flying into a mountain airport descending between two peaks, and the missed approach procedure involves first flying to the airport (which you need the GPS to identify in IMC), then a left turn to a waypoint (which also needs the GPS, but I suppose you could approximate it by holding a heading) -- if you turn too little or too much (or not at all) and go straight, you may also be heading towards some other mountain peaks.

If you are on a GPS approach, and your GPS completely fails, what is the "correct" procedure? Is there a single correct procedure, or can you only rely on your judgement and planning?

Chris

 

[TangoWhiskey]

This question should provide good discussion.

My first thought was "getting to the MSA" for the area... can't hit rocks if you're high enough. In other words, if/when I lost RAIM, I'd be aware of where the high ground was and start climbing on the approach path heading NOW... and be aware of whether or not I could continue to climb straight ahead for a while. In this case, I know that the HIGHEST terrain in the area is straight ahead, so I'd be starting a climb and beginning a turn to the North/Northwest while asking ATC for vectors. Even at 9400' before IPODY, I'm higher than anything to the N/NW [I should say higher than anything on the IAP plate to the N/NW... a check of a sectional would be advised here, preflight, to highten awareness and to know the grid MSA's around the airport, and know where the lower terrain is].

Interesting thing: http://204.108.4.16/d-tpp/0807/06021VDRGA.PDF

There is no MSA circle on this plate. Why?

The GPS Rwy 19 has one, indicating 11,800, so I'd use that in lieu of anything else.

 

[poadeleted20]

If you are on a GPS approach, and your GPS completely fails, what is the "correct" procedure? Is there a single correct procedure,

No.

or can you only rely on your judgement and planning?

...and any other systems you have on board, like a handheld GPS (assuming it was the receiver, not the satellites, that glitched) or your VOR's. And this is another reason why doing all five of the famous T's is so important even when the GPS is doing all the work -- if you've got that timer running since your last fix, you can run a DR from that point. If not, you really are lost.