Spirit follows American Airlines to a downgrade resulting from pricing competition as Southwest adds routes at Dallas Love Field.
American Airlines, unlike most competitors, does not hedge fuel, so it benefits more when fuel prices fall and is hurt more when they rise.
The three global U.S. airlines face plenty of opposition as they battle to end massive subsidies to Gulf carriers.
Southwest told the FAA Tuesday that it had neglected to inspect backup rudder control systems in some Boeing 737s, but then it reached a deal to continue flying the aircraft.
Boeing's 787 Dreamliner enables flights on routes that, initially, don't have huge traffic flows -- routes like Shanghai-Boston and Beijing-San Jose on Hainan Airlines.
A study compiled for American, Delta and United says Gulf airlines Emirates, Etihad and Qatar have collected $39 billion in illegal subsidies, with more to come in new airport spending.
Virgin America shares rise as fourth-quarter results show the carrier has found a niche as a low-cost provider of premium service in highly competitive markets.
The growth of Charlotte as a leading 'New South' city is tied to the growth of American Airlines predecessor Piedmont Airlines and its first flight to London
The last Boeing 767-200 in U.S. passenger service made its last flight on Thursday, as US Airways Flight 767 departed Charlotte for Philly. The aircraft was ordered by Piedmont Airlines.
Spirit Airlines' strong quarter has everybody back in the airline's corner after investors fled following December guidance toward a slight margin decline.