When was the last time you paid special attention to your airline flight number?

Any flight of one to three digits will be operated by the airline itself. But four digit flight numbers means a codeshare flight operated by another airline.

And then, there are the airlines that attach special significance to certain flight numbers, or at least have some fun with them.

At the very least, flight numbers that are easy to remember like Flight 1492 to Columbus or Flight 1776 between Philadelphia and Boston, or an obvious one — Flight 777 to Las Vegas.

But now, the airlines are beginning to run out of flight numbers. With so many scheduled four digit code share flights, they could exceed 10,000 flights, which means some airlines might soon be listing flight numbers with a confusing five digits.