Cost Per Available Seat Mile - CASM

Rules of the airplane: Find your seat, keep your bag under the seat in front of you. Latch your seat belt. And don’t try to buy the pilot a drink (like someone we know did as a joke, only to be interviewed by the TSA for four hours).

Otherwise, the airline will give your seat to someone else to protect its margins. One of the most important financial and efficiency metrics used by airlines is the "Cost Per Available Seat Mile." We typically hear this number every quarter when an airline reports quarterly earnings.

It works like this: The CASM is the quotient of the airlines operating costs over the available seats per mile (ASM). The latter figure is the product of the number of miles in a plane’s flight...times the number of seats on the plane.

The lower this figure is, the more profitable an airline is considered.