Heres what I did to try and find solution
1st- uninstalled Kaip addon and simpilot Result: all good but very boring. Alt of airfield:113.7ft
2nd- default with Kaip addon. Result: fine and boring except for the really good addon
. Alt 113.7ft
3rd- Kaip addon and Simpilot Topo(either way on priority gave the same result) Result: All fine except extra road into airfield which doesnt matter. Alt 113.7ft
4th- Kaip addon and Simpilot topo+mesh(either way on priority gave the same result). Result: Airfield in a hole at alt of 113.7ft and the outside terrain was at 134.8ft?
I managed to fix the problem at Springhill by changing the airport elev and putting a "flatten polygon" to the same alt as the mesh around the airfield on my freeware ADE. But when I tried to do the same with Kaip and try to open 'Kaipara Flats NZKF.bgl' these error messages appeared: