Airline stocks, as measured by the S&P Airline Index, quadrupled from the start of 2012 to a 13-year high reached in January on a perfect mix of falling jet fuel prices and a rising economy.
Industry profit margins at 17 percent are at a record, according to JPMorgan.
"Airline equities continue to screen well on metrics that typically matter: return on invested capital, low valuations, margin expansion, free cash flow, you name it," Jamie Baker of JPMorgan wrote in a note to clients Tuesday.
He added, "The industry has never been this prosperous nor better able to weather exogenous shocks, in our view."
But even as energy prices have continued their decline in 2015, the stocks are starting to show cracks. The airline Index is down 10 percent this year with American Airlines down 19 percent and United Continental down 14 percent.
Analysts fear that for the once perennially plagued industry, this is as good as it will ever get.
Here is what they said...