Narrative:

While enroute and initiating the STAR into hou; we were cleared to coach. The aircraft is equipped with dual garmin 530 units; and programming the STAR did not 'drop' the destination identifier...but kept it in position and created yet another one at the end of the STAR. Therefore when the STAR was initiated; the destination became the next waypoint without being obvious to the crew. Furthermore; when I became suspicious of the navigation the autopilot was following; the display showed the word/name 'coach' displayed upon the direct route to hou...which was where the unit was actually navigating. This made it appear that the unit was indeed navigating to 'coach' when in fact it was navigating to hou directly. The captain was distracted with other cockpit duties during this event and was relying upon me to monitor navigation. Autopilot was tracking the garmin units. To complicate matters; center had switched us to a frequency which was not valid for a center frequency; and although I read-back the frequency; center did not correct the error. (Unknown whose error this was.) I attempted contact and due to other conversation on-freq I believed ATC too busy to immediately respond. In actual fact; this was not a valid center frequency; which was discovered only because ATC (apparently) recognized the error and contacted easterwood tower (whose freq it actually was) who called us in-the-blind and instructed us to return to hou center; which we did. Center advised us we almost penetrated a departure corridor and requested us to telephone them when we landed. We did and resolved the errors. I believe additional causes of this problem was the garmin unit's presentation of the next fix upon a new (erroneous) course-line; and the unit's 'auto-zoom' feature; which may confuse the crew due to changing scale of display. Without that problem I may have realized that the new course was not upon the arrival route. I intend to always keep the second nav unit displaying the active flight plan in order that the dual installation not merely 'copy' the erroneous display of the primary unit; so as to more readily show when a new course does not follow a flight-planned route.

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Original NASA ASRS Text

Title: An HS125 flight crew had a track deviation citing; their Garmin 530 GPS units have some confusing display idiosyncrasies.

Narrative: While enroute and initiating the STAR into HOU; we were cleared to COACH. The aircraft is equipped with dual Garmin 530 units; and programming the STAR did not 'drop' the destination identifier...but kept it in position and created yet another one at the end of the STAR. Therefore when the STAR was initiated; the destination became the next waypoint without being obvious to the crew. Furthermore; when I became suspicious of the navigation the autopilot was following; the display showed the word/name 'COACH' displayed UPON the direct route to HOU...which was where the unit was actually navigating. This made it appear that the unit was indeed navigating to 'COACH' when in fact it was navigating to HOU directly. The captain was distracted with other cockpit duties during this event and was relying upon me to monitor navigation. Autopilot was tracking the Garmin units. To complicate matters; Center had switched us to a frequency which was not valid for a center frequency; and although I read-back the frequency; center did not correct the error. (Unknown whose error this was.) I attempted contact and due to other conversation on-freq I believed ATC too busy to immediately respond. In actual fact; this was not a valid center frequency; which was discovered only because ATC (apparently) recognized the error and contacted Easterwood tower (whose freq it actually was) who called us in-the-blind and instructed us to return to HOU Center; which we did. Center advised us we almost penetrated a departure corridor and requested us to telephone them when we landed. We did and resolved the errors. I believe additional causes of this problem was the Garmin unit's presentation of the next fix upon a new (erroneous) course-line; and the unit's 'auto-zoom' feature; which may confuse the crew due to changing scale of display. Without that problem I may have realized that the new course was NOT upon the arrival route. I intend to always keep the second nav unit displaying the active flight plan in order that the dual installation not merely 'copy' the erroneous display of the primary unit; so as to more readily show when a new course does not follow a flight-planned route.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.