The disparity in size between the low-priced airlines and the top firms underscores a fissure in the industry separating budget carriers in select markets from the major airlines that dominate flight offerings nationwide, Mike Boyd, president of aviation consulting firm Boyd Group International, told ABC News.

Spirit Airlines said Monday that it's filed for bankruptcy protection and will attempt to reboot as it struggles to recover from the pandemic -caused swoon in travel and failed attempts to sell itself to other carriers.

The company has reassured passengers that its Chapter 11 bankruptcy will not affect their bookings and that staff will still be paid.