Delta Air Lines may have charged some frequent flyers higher airfares than other customers for almost three weeks because of a glitch, which has triggered questions about the complexity of flight searches.

Reports surfaced last week from two business travelers who noticed prices on routes they were searching were different depending on whether or not they were logged into their Delta frequent flyer accounts. Prices were higher when logged in on Delta's website versus anonymous price searches without logging in.

On Friday, Delta offered a detailed explanation of the discrepancy. Although the problem has been solved, it brings into light the complexity of airline pricing.

Delta and other airlines use third-party companies such as Expedia , Orbitz and Google's ITA Software to deliver results, when customers search for flights. Those providers then search through the virtually limitless amount of flights, routes and fares for the queried origin and destination; and display the results to the customer on the airline's website.

Delta considered switching its search provider, so the company ran a side-by-side experiment withanother providerbeginning April 20, Bob Kupbens, the airline's head of e-commerce told The Associated Press . Delta declined to name either of the two search providers used.

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