Five airlines are at the center of a newly opened federal investigation into price-gouging for their actions in allegedly raising airfares following the May derailment of an Amtrak train in Philadelphia, an accident that killed eight people and injured 200 others. The U.S. Department of Transportation sent letters to JetBlue, Southwest, Delta, United and American airlines, seeking pricing information for air travel routes most likely affected by the temporary shutdown of rail travel along Amtrak’s Northeast Corridor.