As the old stock market joke goes, all they have to do is start with a billion and invest in an airline, and that's it.

On a more serious note, Delta has done its utmost to prove the adage wrong, not without merit it must be said, and thanks also to a sector that is rather consolidated in North America, which has the advantage of reducing pressure on prices and explains Delta's strong operating margin.

In the fifteen years from 2010 to 2025, i.e. the sequence following the great financial crisis of 2008 and including the pandemic, the company has doubled its sales and operating profit, and reduced its number of outstanding shares by a quarter.

Not a stratospheric performance, to be sure, but in a sector that has long since turned into a graveyard of illusions - and shareholders - it commands a certain respect.

Free cash flow, however, remains the ultimate yardstick, and has been erratic since the pandemic - an episode during which Delta burned $5.6 billion: here too, things could have been worse. This misadventure was all the more ill-timed as it came after a series of share buy-backs and at the start of a major fleet renewal plan.

Fortunately, the unexpected flexibility of the capital markets at the time enabled Delta to raise $20 billion in new money via very low-cost debt, in addition to $5.6 billion in subsidies from the federal government. This saved the company from the worst. However, the dividend and share buybacks had to be suspended.

The company is now entering 2025 and the new cycle under less favorable auspices than before. Inflation is hitting at all levels; interest rates are rising after a decade and a half of virtually free money; while pressure from low-cost operators is eroding the margins of the major airlines.

That said, the past fiscal year has been rather good. Business travel and transatlantic routes were full, not least because the dollar's very favorable exchange rate attracted record numbers of American tourists to Europe; Delta was less affected than its peers by Boeing's taming difficulties; and the company has a very lucrative frequent flyer program with Amex.

MarketScreener analysts point out, however, that most of this year's gains stem from a persistently low oil price, rather than from any real operational improvement. In this respect, here as elsewhere - but even more acutely here - it would be dangerous to extrapolate the year's result on a long-term trend.

Delta, however, lends itself to the exercise and anticipates annual free cash flow of between $3 and $5 billion per year until 2028-2030. This brings the current enterprise value of $62 billion to a multiple of twelve to twenty times free cash flow - an unattractive valuation level.

As the company has clearly stated that rapid deleveraging is at the top of its objectives, we assume that it will be some time before the return of capital to shareholders resumes.