Delta Airlines has one of the oldest fleet of planes in the U.S. Delta is turning this into a strategic move by having to invest less in new planes and with the ability to get good flight performance from older planes with proper maintenance. Delta says it is saving about $1 billion by acquiring 49 MD-90 planes with age of about 13 years from China Southern and other global airlines, compared to the cost of buying new planes. The estimate is that it is about 10% cheaper per seat to run these planes than new 737's, when the cost of buying planes is figured in. It also took over the leases for 88 Boeing 717's with average age of 11 years from Southwest. The focus at Delta is on profitability and debt reduction by selecting routes carefully, avoiding unprofitable ones, using tight cost management. Delta is on its third year of making profits and is on plan for reducing its debt from $17 billion in 2009 to $10 billion by 2013. The older Delta fleet is also the most punctual of the large airlines in the U.S., with 86.3% of flights on time in the Jan-Sept. 2012 period. Fitch Ratings raised Delta's credit ratings to B-plus and says Delta is "the strongest player in the much improved airline industry in the U.S."...