»»Delta Air Lines Will Only Accept Credit Cards on Domestic Flights
Cashless cabins are making their way through most airlines.
Beginning Dec. 1, Delta Air Lines will only accept credit cards for on-board food and alcoholic drink purchases on all domestic Delta and Northwest flights.

Delta will still take cash and credit on international flights; and it does not accept credit cards on Delta Connection flights on its regional carrier partners such as Atlantic Southeast Airlines.
In order to process the in-flight transactions, Delta flight attendants will use hand-held credit card readers.
Other airlines that have gone to cashless cabins include JetBlue, AirTran Airways, American and United. (source)
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