Deputy U.S. Transportation Secretary John Porcari has been recused from examining the pending antitrust application led by British Airways PLC (BAY.LN) and the American Airlines' unit of AMR Corp. (AMR).

Porcari joins U.S. Transportation Secretary Ray LaHood on the sidelines of the high-profile case. Both men had conflicts of interest due to their backing of the application, made before they took office.

DOT is expected to make a decision by late October on the airlines' plan to coordinate trans-Atlantic services with members of their Oneworld alliance. The ruling is viewed by the industry as a key test of evolving U.S. aviation and competition policy.

The U.S. Justice Department weighed in this year with a series of objections to a similar application by members of the Star alliance, led by United Airlines parent UAL Corp. (UAUA) and Deutsche Lufthansa AG. (LHA.XE).

DOT has final jurisdiction in airline competition matters, but comments from Justice on the BA-AMR case are keenly anticipated after most of Justice's objections were rejected by transport officials in approving the expansion of Star to include Continental Airlines Inc. (CAL).

The final deliberations on Oneworld will be made without DOT's two top officials. The U.S. Transportation Department confirmed Wednesday that Porcari had been recused because he filed a comment on the case last November, when he was transportation secretary for the state of Maryland.

LaHood stepped back from the case earlier this year, some months after his own comments on the matter were first disclosed.

BA and American declined comment.

This is the airlines' third effort to secure immunity and gain parity with members of Star and SkyTeam, the third global alliance. Two previous attempts were dropped after the concessions sought from regulators were seen as too onerous.

-By Kaveri Niththyananthan, Dow Jones Newswires; 4420-7842-9299; kaveri.niththyananthan@dowjones.com

(Josh Mitchell and Doug Cameron contributed to this article.)