What Maptech program and version number (which can be found in the Help> About menu) are you using?
If it is Terrain Navigator, first ensure that you have the latest version available from this website in the downloads section, version 5.03. Once 5.03 is loaded, you will need to select Plane as the symbol in Tracking Preferences, then hit Apply, then OK. Then begin the real-time positioning.
Thanks,
- Mike