Twice as many "Diamond" customers means twice as many requests for premium seats, upgrades and access to airport clubs. It also means higher costs for the company, at a time of sharply rising fuel prices and the consequent need to save money, and more complaints from former beneficiaries who take a dim view of the many newcomers to their turf.

However, Delta Air Lines took a drastic decision at the beginning of September: to limit access to its SkyMiles program from 2025 onwards, linking frequent flyer status solely to passenger spending (not counting flights purchased by passengers), and to reserve clubs for Delta credit card holders, as other airlines have done before it.

The reaction was immediate: online forums, social networks and the carrier's customer service department were all taken over by disgruntled travellers. And as if on cue, the airline's competitors, including JetBlue and Alaska, took advantage of the situation to woo disappointed customers with their own loyalty offers.

Such was the uproar that Ed Bastian, the group's CEO, publicly acknowledged the error and announced changes to come. However, the company's cash position must be preserved, and Premiums must continue to be offered a level of service they feel is appropriate. It promises to be a complex equation. Especially since Delta announced two weeks ago that it was lowering its third-quarter earnings forecasts.