You just booked a flight on one of the major U.S. carriers. Instead of going with a no-frills airline like Spirit, you decided to treat yourself to more legroom and presumably greater comfort. You are probably envisioning a posh cabin on a brand new 787 Dreamliner, seasoned pilots, in-flight meals, smiling flight attendants... you know, everything you see in the commercials! Not always. Your flight or part of your flight (especially connecting flights) may be operated by a third-party, contracted as part of a lowest-bidder model, where costs are shaved everywhere (e.g. pilot training, aircraft maintenance). You may end up on a cramp 1 & 2 seater, with tiny overhead bins, a single overworked flight attendant, and worst of all, no food (never mind the seat-back entertainment system you were looking forward to sampling)!
Republic Airways
American Airlines = American Eagle
Delta = Delta Connection
United = United Express
SkyWest Airlines (SKYW)
Delta = Delta Connection
Alaska Airlines = Alaska SkyWest
American Airlines = American Eagle
United = United Express
Air Wisconsin
American Airlines = American Eagle
CommuteAir
United = United Express
GoJet (Trans States)
United = United Express
Mesa Airlines (MESA)
United = United Express
PAL Airlines
Air Canada = Air Canada Express
Jazz Aviation (Chorus Aviation, CHR)
Air Canada = Air Canada Express
Excluded
Endeavor Air => Owned by Delta
Envoy Air, Piedmont Airlines, PSA Airlines => Owned by American Airlines
Horizon Air => Owned by Alaska Airlines
WestJet Encore => Owned by WestJet
Pacific Coastal Airlines => WestJet Link planes can't seat more than 34 passengers.
No Longer Operating: ExpressJet, Trans States Airlines (see GoJet), Compass Airlines