Atlanta-based Delta Air Lines Inc. plans to invest $1 billion over the next three years for a series of improvements designed to make flying more comfortable, particularly for international travelers.

The airline announced Monday that it is installing full flat-bed seats in BusinessElite on 90 trans-oceanic aircraft. Unlike older reclining seats, the new seats fold down into a bed that is completely flat for sleeping.

Delta will also add audio- and video-on-demand service in economy class on 16 Boeing 747s and 52 Boeing 767s. It will upgrade seating, lighting and cabin amenities on 269 planes it obtained in the merger with Northwest Airlines Corp. Delta will install vertical extensions of the wingtips on 170 Boeing 767s, 757s and 737s to increase the range by improving fuel efficiency.

The carrier will also add first-class cabins to 66 aircraft operated by its connecting airlines ASA, Comair and Skywest and renovate and expand the Los Angeles Sky Club lounge while putting new Sky Club locations in Seattle, Philadelphia and Indianapolis.

“Delta’s planned fleet and product investments mark the most significant investment we have made in our customers in more than a decade,” Delta CEO Richard Anderson said in a news release. “Our premium travelers tell us that the comfort of a flat-bed seat with direct aisle access, a first-class experience on regional jets and in-flight entertainment are important factors in their choice of carrier.”

The upgrade costs are in line with Delta’s capital expenditures in the past, said the airline’s president, Ed Bastian in a news release. “Rather than invest in new aircraft, Delta will be spending its capital to improve the quality and consistency of the on-board product and efficiency of the aircraft we already own,” he said.