Belfast OSM2CITY + OSM2ROADS for FlightGear. Add Belfast-fg-CustomScenery/Belfast to $FG_SCENERY. Make sure to use TerraSync terrain, right below Belfast. As such: BELFAST TERRASYNC
This will ensure you have Terrain and existing Objects!
There is also a EGAC.btg.gz file; you may overwrite the TerraSync EGAC.btg.gz if you wish...