In my forty-five years in and around this airline caper it is my observation that profits can be had in making ground equipment, supplying catering (sometimes), providing cost + ground handling services, consulting to the people with hundreds of aeroplanes and no profit, navigation services, government departments, nav charges, insurance, pilot training, simulator training, crewing agencies, "expert" commentary for hire (that means you, GT!), I.T., reservations systems, security.
In fact, just about anything except operating aeroplanes. Sure, having an airline is sexy, and often fun, but ever since the Wright Brothers not many people have made a go of it without government patronage or court protection (chapter 11 in the US). The problem with the industry is the low barrier to entry of a seemingly endless parade of monied fools who believe that they alone hold the elusive key to aviation success. And the occasional group of investors too blasé to see what psychopaths they have entrusted with their airline.