If you are looking for the subtitle file specifically for this version, you should look for .srt files that match the "YTS" or "YIFY" timing. Common sources for these include:
Filter by the exact filename to ensure the dialogue syncs perfectly with the video. subtitle Flightplan.2005.720p.BluRay.x264.[YTS.AG]
The original download page often provides a direct link to the synchronized subtitle file. If you are looking for the subtitle file
The story follows Kyle Pratt (Jodie Foster), an aircraft engineer who is flying from Berlin to New York with her 6-year-old daughter, Julia, to bury her recently deceased husband. After falling asleep for a few hours, Kyle wakes up to find Julia missing. subtitle Flightplan.2005.720p.BluRay.x264.[YTS.AG]
Search for "Flightplan" and look for the BluRay/YIFY tag.