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Aviation Alerts and Advisories

Service Advisory 1558: Procedures with Headings and Altitude Legs

 GPS400(W), GNC420(W), GNS430(W), GPS500(W), GNS530(W), GTN625, GTN635, GTN650, GTN725, GTN750

 This advisory provides clarification regarding the operation of Garmin GNS 400(W)/500(W) and GTN 6XX/7XX navigators while flying procedures that include heading and altitude-based legs.

 The following are best practices for Garmin GNS and GTN systems used for primary navigation guidance during instrument procedures:

  • Before using the GTN or GNS navigation system for primary navigation guidance for any part of an instrument procedure, always compare each leg of the applicable and current published charted procedure to the flight plan displayed on the navigator. The navigation system may not support some specific navigation leg types, it is important to understand how each leg will be navigated prior to conducting the procedure.
  • When a procedure includes navigation legs defined by a specific heading, or that end at a specific altitude, it is important to understand how the navigation system will behave and how that system behavior can affect autopilot operations, if coupled.
  • Before manually sequencing a leg in a procedure, verify what specific navigation guidance will be provided by the GNS/GTN for that leg, and activate the leg only upon arrival at the appropriate point in the procedure.
  • Use available documentation, including Flight Manual Supplements, to understand the operation of the specific GNS or GTN system installed in the aircraft.
  • Learn and gain a thorough understanding of instrument navigation operations and general system behavior on the ground using the GNS or GTN PC Trainer provided free of charge at

For more information regarding instrument procedures, refer to the GNS 400(W)/500(W) Series and GTN 6XX/7XX Series Instrument Procedure Leg Awareness document (Garmin P/N 190-02052-00) available on .

Download 1558A Download 190-02052-00_1