How much data are you likely to deal with? Is this a static file or is it updated in real-time?

If it's a static file, and not too large, just read the entire file into memory. If it's being updated dynamically (say it's a pipe), use a data structure (a hash perhaps?) and keep as much data as required in memory. Depending on the number of flights you've got to process, you could probably keep the past twenty-four hours of data (iirc, the busiest airport in the US handles no more than a couple of thousand flights per day).