Not much mention in this thread about high labour costs, which is, in my experience a massive drag on company solvency if out of kilter with competitors.
Delta and NWA operate the same aircraft types, offer the same fares (it's a competitive market), and suffer the same fuel cost as Southwest, JetBlue, AirTran, etc. but have payroll costs that are massive in comparison. Well-paid and under-employed staff with perks designed in the fifties and sixties create a burden when trying to compete with locos.
As many British workers discovered in the 70s and 80s, a strong union often means a weak company. And weak companies fail.