DALLAS (

TheStreet

) -- If

Delta

TST Recommends

(DAL) - Get Report

actually wants to buy into

Japan Airlines

, it could have a battle on its hands.

American

(AMR)

, currently a partner with Japan in the Oneworld alliance and through a code-share, which enables the carriers to write tickets on one another's flights, would likely be seriously hurt by such a deal, because its ability to carry passengers into Asia would be imperiled.

"This would be a body blow to American, and it would decimate Oneworld," said aviation consultant Robert Mann. "American would have to go to the mat to prevent it."

A series of media reports on Friday said Delta is discussing the purchase of the biggest stake in financially troubled Japan Airlines, the biggest carrier at Tokyo's Narita, Asia's most important airport because of its importance to Japan and its web of connections throughout the continent. Delta has not commented, and a JAL spokesman denied the report to several news outlets.

American spokesman Tim Smith also declined to comment, except to say that "Japan Airlines has been an excellent partner, both for American and Oneworld."

The real problem is that the world has three international aviation alliances and just two major Japanese carriers, JAL and All Nippon Airways. JAL is a key member of Oneworld, along with American and

British Airways

. ANA is in the Star Alliance with

United

(UAUA)

and

Lufthansa

.

SkyTeam, the third alliance, includes Delta and

Air France

. Some news accounts have AirFrance involved with Delta in the JAL investment.

For American, the partnership with JAL provides a key method to carry passengers beyond Tokyo to points in Asia. In 2007, American moved into a JAL terminal at Narita, enabling it to reduce connect times to many JAL flights. At the time, Don Casey, then managing director for international planning, declared: "When you look at the three alliances, all three have about a third of the U.S.-to-Japan (market). That is why we are so excited about having Japan come into Oneworld."

Currently, American offers five daily round trips to Tokyo, including two from Dallas and one each from Chicago, Los Angeles and New York. It also code shares with JAL on several flights from the same gateways. From Narita, JAL serves dozens of cities in Asia.

Delta already operates a small hub at Narita, the result of its 2005 merger with Northwest, which obtained rights to fly beyond Tokyo into Asia in 1947. Delta serves Narita from seven cities in North America, Honolulu, and 14 cities in Asia.

"If you figure in all that traffic originating in Japan and all the traffic JAL can pull into its hub and then you add the Delta traffic from the U.S., it's a double whammy," Mann says. "It helps you in Asia, and gives you the best service from the United States"

Delta's offer surfaced at a time when the U.S. and Japan are engaged in bilateral talks, which could increase the amount of competition between the two countries, although historically Japan has been reluctant to liberalize air traffic agreements. No doubt Delta's offer for JAL involves a calculation regarding the talks.

Another factor at play is that over time, the value of a strong presence at Narita is expected to diminish, as airplanes like the Boeing 787 and the Airbus A350 provide U.S. carriers with the capacity to serve key markets in Asia with non-stop flights from U.S. hubs.

At the moment, the first 787 delivery, which will be to ANA, is 2 1/2 years behind schedule, and A350 deliveries are even further off. However, the impact of those delays is mitigated by the current economic slump, which has reduced trans-Pacific traffic.

-- Written by Ted Reed in Charlotte, N.C.

.