Today, Delta Air Lines (NYSE:DAL) announced it would be spending $770 million through 2016 to update and upgrade the interiors of its Boeing 757 and 737 aircraft, and its Airbus A319 and A320 aircraft, in an effort to improve the comfort of its passengers. Changes include more overhead bin space for carry-on luggage and new "slim-line" seats, which some people have criticized as contributing to a less comfortable flight.

The airline said that the improvements to 225 domestic narrow-body aircraft will benefit the customers in both the first and economy class cabins. As a part of the investment, Delta will give power at every seat, add new "slim-line" seats that include adjustable headrests, improve and update lavatories, while also adding more efficient and space-saving galleys. In addition, after the modifications are complete, Delta's entire 73-plane fleet of 737-800 aircraft will have in-seat video, and access to satellite television.

Delta will update its 57 A319 and 69 A320 planes, which will include upgrades for more carry-on baggage capacity (which is also true of the 757-200 models). In addition, every A319 and A320 model will feature a widening of its seats from 17.2 to 18.0 inches.

Delta says new overhead bins will increase carry-on baggage space by 50% to 60%.

Some questions have arisen surrounding slim-line seats, which generally are less bulky and weigh up to 30% less than traditional seats. This allows airlines to add more seats onto the planes, while also saving on fuel costs. This benefits the airlines due to both increased revenues and lower costs; however, some passengers have called into question the more crowded nature of the planes. 

The announcement today follows more than $3 billion of investments that Delta has made since 2010 in an effort to improve both the experience of its customers on the planes, as well as in the terminals. This includes a $100 million investment and renovation at New York's LaGuardia airport, as well as the improvements seen at 50 Delta Sky Clubs.

"We're continuing to make smart long-term investments in our products and services to meet the expectations of our customers," said Delta Chief Revenue Officer and Executive Vice President Glen Hauenstein in a statement. "In just six years, we will have made updates to interiors throughout Delta's fleet giving customers improved comfort and more options to work or relax and be entertained."

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