twistedenginestarter,
at least one passenger carrier – Allegiant in the USA – uses rather old aircraft (MD-80) and a low utilization strategy. And Allegiant is profitable although with a different business model compared to other LCC.
SEC Info - Allegiant Travel CO - 8-K - For 11/16/07 - EX-99.1
(browse down and you find more info why Allegiant has chosen the MD-80 family)