Hearing starts legal fight to the challenge by the U.S. Justice Department to airlines' proposed merger.
$11 billion merger to create the world's largest carrier gets go-ahead after surrender of slots on one route, sources say.
Passengers face delays of 2 hours or more at some airports due to air traffic staff shortages.
The merger would reduce the number of major U.S. airlines to four: the new American, United, Delta and Southwest.
Federal rules barred the type of batteries used to power Boeing 787 electrical systems from being carried as cargo on passenger planes.
Airlines say they have started confidential merger talks. But a deal, which would create one of the world's largest airlines, is still far from reality.
