No-frills air travel pioneer Spirit Airlines filed for bankruptcy protection on Monday, after struggling with a long run of quarterly losses, a failed merger attempt and upcoming debt maturities.

The country's largest budget carrier will cut its year-end schedule by 20 percent as it struggles to return to profitability.

The long-anticipated bankruptcy of ultra-low-cost carrier Spirit Airlines (NYSE:SAVE) is reverberating through the airline sector, with rival Frontier Group Holdings (NASDAQ:ULCC) also suffering a double-digit loss in sympathy with an 18% drop in Spirit (SAVE).