The global airline sector has lost a fifth of it's market capitalization, or $40.6 billion, in February, says AJ Bell, a UK-based investment firm.

The sector's current valuation stands at a 5-year low and is 45% below its January 2018 peak of $205 billion, as benchmarked by the S&P Global 1200 airlines index.

This is a massive contrast to just 3 years ago when American Airlines' CEO Doug Parker argued that the industry will be profitable in good times and bad, says Russ Mould, investment director at AJ Bell.

Industry body International Air Transport Association (IATA) estimates airlines could lose between $63 bln and $113 bln in revenue for passenger traffic globally in 2020.

 Shares of American Airlines, Delta Air Lines Inc, and United Airlines fall between 2% and 3% premarket on Friday.