What - O, its not a downward spiral. What investors chase is returns commensurate with risk and capital appreciation in line with global growth of GDP.
If the expected rate of return for airline investment is 3.5% and GDP growth is 3%, then if you achieve these numbers you are doing OK.
What appears to be happening to airlines is that we are still feeling the after affects of the invention of the low cost carrier. Until the dinosaurs reinvent themselves in this mode there will continue to be angst and tears.