Narrative:

Prior to departure; I loaded the flight plan into the GPS; a GPS-155XL. This model GPS requires the data cards to be changed when crossing the border between the us and mexico.after crossing nelyn intersection; the captain instructed me to finish inputting the flight plan into the GPS. I tuned the act VOR into both navigation radios; and the 357 radial (inbound) was selected. After swapping the data cards; I input the remainder of our flight plan and selected direct to act from the flight plan page. I selected the CDI selector back to GPS. I put the USA card back into the GPS and the captain tried to review what I had input. Because the cards were swapped; all of the waypoints in mexico showed as 'locked.' I swapped the cards again so the captain could see what input was. We incorrectly assumed that the GPS would sequence to hoary intersection as it was listed as the next fix in the GPS flight plan. Because the mex data card was still installed it did not; and as a result; the aircraft continued on a 177 track for approximately 5 minutes rather than the 193 course depicted on the SID. At that time; I noted that we had passed act; and we realized the GPS failed to sequence to hoary intersection; instead showing a from indication and the act VOR as the active waypoint. We began a right turn in an attempt to rejoin the departure as fort worth center called to advise us that we were approximately 8 miles left of course. As I tried to correct the issue with the GPS by switching the data cards; we were cleared direct [to our destination].one factor affecting our performance during this incident is a lack of recent experience with this GPS. In our fleet [majority] are equipped with a GNS430 GPS; and this aircraft is equipped with a GPS-155XL. While the operation is similar in many ways; they also differ in several ways; notably the need to switch the data card when traveling across the border. In retrospect; we should have waited until getting closer to mexico to switch the cards and load the remainder of the flight plan. Additionally; though the pilot was receiving navigation information from the GPS; my CDI was receiving information from the navigation radio. And; as such; I failed to effectively monitor our position relative to act; and did not note station passage.

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Original NASA ASRS Text

Title: First Officer described the difficulties using the GPS-155XL on a cross border flight to Mexico. The unit requires that data cards be switched prior to loading the Mexican portion of the flight plan. Errors are made resulting in a track deviation.

Narrative: Prior to departure; I loaded the flight plan into the GPS; a GPS-155XL. This model GPS requires the data cards to be changed when crossing the border between the US and Mexico.After crossing NELYN intersection; the captain instructed me to finish inputting the flight plan into the GPS. I tuned the ACT VOR into both NAV radios; and the 357 radial (inbound) was selected. After swapping the data cards; I input the remainder of our flight plan and selected direct to ACT from the flight plan page. I selected the CDI selector back to GPS. I put the USA card back into the GPS and the captain tried to review what I had input. Because the cards were swapped; all of the waypoints in Mexico showed as 'locked.' I swapped the cards again so the captain could see what input was. We incorrectly assumed that the GPS would sequence to HOARY intersection as it was listed as the next fix in the GPS flight plan. Because the MEX data card was still installed it did not; and as a result; the aircraft continued on a 177 track for approximately 5 minutes rather than the 193 course depicted on the SID. At that time; I noted that we had passed ACT; and we realized the GPS failed to sequence to HOARY intersection; instead showing a from indication and the ACT VOR as the active waypoint. We began a right turn in an attempt to rejoin the departure as Fort Worth Center called to advise us that we were approximately 8 miles left of course. As I tried to correct the issue with the GPS by switching the data cards; we were cleared direct [to our destination].One factor affecting our performance during this incident is a lack of recent experience with this GPS. In our fleet [majority] are equipped with a GNS430 GPS; and this aircraft is equipped with a GPS-155XL. While the operation is similar in many ways; they also differ in several ways; notably the need to switch the data card when traveling across the border. In retrospect; we should have waited until getting closer to Mexico to switch the cards and load the remainder of the flight plan. Additionally; though the pilot was receiving navigation information from the GPS; my CDI was receiving information from the NAV radio. And; as such; I failed to effectively monitor our position relative to ACT; and did not note station passage.

Data retrieved from NASA's ASRS site 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.