Carrier that offered pioneering coast-to-coast service beginning in the 1930s

TWA

This airline was once a major rival to Pan Am and famously introduced the first nonstop transcontinental flights using the Lockheed Constellation. Its initials stood for "Trans World Airlines."

This clue points to TWA, or Trans World Airlines, which became famous for launching one of the first regular coast-to-coast passenger flights in the U.S. during the 1930s. The term "carrier" simply refers to an airline, and "pioneering" hints at TWA’s early role in connecting major cities like New York and Los Angeles. The answer is a well-known abbreviation in aviation history, making it a straightforward fit for the clue.