Last year, Delta was able to get access to overseas routes at Narita airport in Tokyo because of its acquisition of Northwest Airlines, and the proposed transaction with JAL would give it more reach within Asia's largest travel market. The discussions between the two airlines are not public, according to a Bloomberg News report, and Delta did not comment. JAL's spokesman, Satoru Tanaka, says that the report is not true.

If completed, the investment and operating relationship would bolster the SkyTeam airline alliance, of which Delta is a member, as it does not currently have a flagship airline in Japan. JAL is a member of the Oneworld Alliance, which includes American Airlines and British Airways. American Airlines wouldn't comment on whether JAL reached out to it for an investment.

JAL could probably use the help. It put up a $1.09 billion loss in the first quarter, its greatest in six years, and both business and leisure travelers are staying on the ground these days. The Japanese government established a panel of legal and academic minds last month to restructure the carrier, which has shown losses in three of the past four years.

Even if both Delta and JAL are willing to take the plunge, other barriers exist. Regulatory approval might be difficult to win, as Delta and JAL are the largest airlines in their domestic markets. There is also speculation that Delta is using this to disrupt the "open skies" negotiations between the United States and Japan. The plan would loosen restrictions on flights between the two countries and would help some of Delta's competitors.