Garmin GPS 155XL Pilot's Manual & Reference

Also see for GPS 155XL: Maintenance manual Installation manual Installation manual

Basic Rules of GPS ApproachesThe GPS 155XL is the first GPS certified to meet the requirements of TSOC-129a Category A1. When using the GPS 155XL for non-precision approaches,you’ll encounter two types of approaches: overlay approaches (based on existing pro-cedures) and GPS approaches (new approaches designed specifically for GPS). TheFAA has approved a large number of overlay approaches, with plans to add as manyGPS approaches as possible to take advantage of the safety and convenience of GPS.Flying a GPS approach is not difficult, and varies from conventional approachesonly in the operation of the equipment being used. Although you’ll often be followingthe same flight path used in conventional approaches, the equipment operation pro-cedures will be different from typical NDB or VOR approaches.The following definitions, guidelines and examples that follow will help youunderstand the basic rules of GPS approaches, and guide you through some typicalapproaches. Think through the approach examples— this will assist you in gettingthe greatest benefit from the GPS 155XL. There are a few basic rules that apply to allGPS approaches. Remembering these rules will assist you in understanding theapproach procedures and ensure the greatest margin of safety for your flight.• The approach to be flown must be in the aviation database, and the databasemust be current.• You may select an approach any time after the destination airport is selected.If the GPS APR switch does not indicate an ‘ARM’ status within 2 nm inboundto the final approach fix, you run the risk of flying a non-approved approach.• When performing an approach, the GPS SEQ switch must be set to the AUTOposition with the FAF as the active to waypoint for the approach to go active.If the switch has not been set to the AUTO position 2 nm before the FAF, theCDI scale transition will be compressed, making the CDI change more abrupt.(continued on the next page...) 77SECTION5APPROACH NAVBasic Rules ofGPS ApproachesCDI Scale ramping during approach.0.3 nm30 nm2 nmFAFMAP1 nm1 nm5 nm1 minute