Narrative:

On the downwind or base vector; the controller advised us to expect direct chnzo for the RNAV 13 at lga. I didn't understand what he said and queried the captain. We found the fix on the approach plate. Shortly thereafter approach cleared us direct chnzo which was not in the FMS. We entered it manually. A couple miles outside of meatz the tower asked if we were tracking the approach okay. He said the approach controller was asking. I looked at the approach plate and saw 232 degrees from chnzo to rabby and then 179 degrees to meatz. We were flying a course closer to 200 degrees to meatz. I verbalized this to the pilot flying while we continued to configure. We were VMC and continued the approach. The captain suspected that rabby dropped out of the FMS. We failed to ensure all the approach fixes were still in the FMS after adding a fix. We also deleted a discontinuity after added chnzo. The FMS could have sequenced causing us to delete rabby. I failed at cross checking the aircraft path against the approach plate. This event is a strong reminder for me to be more vigilant when making changes to the FMS during the approach phase. I could also reduce the workload by having all the approach fixes loaded until we know where the aircraft will intercept the approach path. I will also work to improve my monitor/crosscheck skills in order to make sure the aircraft path matches the approach plate.

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Original NASA ASRS Text

Title: Flight crew reported using incomplete FMC programming after receiving a vector to a different initial fix on an RNAV-GPS approach.

Narrative: On the downwind or base vector; the controller advised us to expect direct CHNZO for the RNAV 13 at LGA. I didn't understand what he said and queried the Captain. We found the fix on the approach plate. Shortly thereafter approach cleared us direct CHNZO which was not in the FMS. We entered it manually. A couple miles outside of MEATZ the tower asked if we were tracking the approach okay. He said the approach controller was asking. I looked at the approach plate and saw 232 degrees from CHNZO to RABBY and then 179 degrees to MEATZ. We were flying a course closer to 200 degrees to MEATZ. I verbalized this to the Pilot Flying while we continued to configure. We were VMC and continued the approach. The Captain suspected that RABBY dropped out of the FMS. We failed to ensure all the approach fixes were still in the FMS after adding a fix. We also deleted a discontinuity after added CHNZO. The FMS could have sequenced causing us to delete RABBY. I failed at cross checking the aircraft path against the approach plate. This event is a strong reminder for me to be more vigilant when making changes to the FMS during the approach phase. I could also reduce the workload by having all the approach fixes loaded until we know where the aircraft will intercept the approach path. I will also work to improve my monitor/crosscheck skills in order to make sure the aircraft path matches the approach plate.

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.