When loading a GPS approach the system will allow modification to the Active Flight Plan GPS approach service level without disabling SBAS. For example, a crew could choose to execute an approach marked LPV as though it were an LNAV+V approach. The Service Level Button is accessed through the menu button on the approach window. The service levels and vertical sources available in this selection are limited to those applicable to the approach, and invalid combinations (such as executing an LPV with Baro vertical guidance) are prevented. The Approach Mode default setting is 'Auto', for which the optimal service level and vertical source will be displayed, as determined by the system for the selected published approach.