A key point to note is that with this 'terrain' database derived from Nasa, it has missing data and so cannot be deemed reliable for flying in low visibility below MSA (even if you have a very accurate position derived from EGNOS, the EU equivalent of WAAS which is fully deployed but not yet certified for use with safety-of-life operations - see
www.esa.int/esaNA/SEMKMQWO4HD_egnos_0.html )
On various trips around Scotland, for example, I have found the following very substantial islands/hills missing (i.e showing clear blue water
) :
Scarba (1500' island just north of Jura)
Muck (450' island south of Rum and Eigg)
Scalpay (1300' island NW of Isle of Skye, Broadford airfield)
Then on another recent trip I departed on a leg from Dresden to Hungary which took us south into the Czech Republic. We were VFR as we headed over ground rising from about 1000' to 3000', but with plenty of steep valleys. Prague Information were keeping us very low and I observed there were several substantial hills up to 2800' or so that the Garmin 496 and 530 'terrain' functions were indicating as part of the valleys - i.e absolutely no indication of these massive obstructions.
I did contact Garmin and asked them about the fact that Scarba, for example, was missing off the terrain and map pages even though it was a pretty impressive rock rising steeply out of the water to 1500'. They pointed out that the GPS units are for VFR use only and to read the warnings carefully (see below) (and they suggested updating to the latest database, which I did but this didn't sort the problem)
So in my view the terrain function is fine to use as a elevation 'trend' indicator but stick to VFR navigation for vertical separation. If you're IMC then MSA is the only way to do it. If you're flying IFR then I don't really see what the use of synthetic terrain is . . . at least until they can guarantee it is 100% correct. But it does look very pretty !!
Garmin warnings:
"For VFR use only as an aid to prudent navigation. All information is presented for reference only. You assume total responsibility and risk associated with using this device. Terrain and obstacle data are provided only as an aid to situational awareness"
"Terrain data MUST NOT be used as the sole basis for decisions or maneuvres to avoid terrain or obstacles. Terrain data MUST NOT be used for navigation"
Drambuster