Shuttle by United was an "airline within an airline" operated as a subsidiary of United Airlines from 1994 to 2001 along the West Coast of the United States. It operated from San Francisco International Airport and Los Angeles International Airport. Shuttle's fleet consisted of Boeing 737-300s and 737-500s. The service was eventually renamed United Shuttle before it was shut down by United and its aircraft returned to mainline service with the airline.

Song, LLC, was a low-cost air service within an airline brand owned and operated by Delta Air Lines from 2003 to 2006. All Song flights were operated by Delta. Song's main focus was on leisure traffic between the Northeastern United States and Florida, a market where it competed with JetBlue Airways. It also operated flights between Florida and the West Coast, and from the Northeast to the West Coast.