Avoid proprietary FBL entirely. If you control map creation, store originals as GeoTIFF + OSM XML or GeoPackage to prevent format lock-in.
Use a hex viewer or fblinfo.exe (from FBL2IMG package): fbl map files download convert
[FBL + FDA + FPA] ↓ iGO Map Tool (export to KML) ↓ KML file ↓ QGIS / ogr2ogr ↓ GeoJSON / Shapefile / GPKG Avoid proprietary FBL entirely