He said it seemed so absurd considering that airport security would never allow any passenger to check in an axe.
I didn't have an answer so I googled Airplane security axe. How wonderful is the INTERNET because his question was answered.
In every plane there is an axe called the crash axe. It's found inside the cockpit.
So the next question is: Why wasn't the axe in LOST inside the cockpit? Or could this just be a blooper?