LAS VEGAS (KTNV) — Delta Air Lines is taking aggressive action to address toxic fumes in airplane cabins by replacing auxiliary power units (APUs) on more than 320 planes in its Airbus fleet, an ongoing project that is now more than 80% complete.

The initiative targets what flight attendants and pilots call the "dirty sock smell" — a health and safety hazard caused by toxic smoke, fumes and odors leaking into airplane air supplies.

13 Investigates | Darcy Spears reports the latest on the airline industry, making changes to improve air quality Big changes coming to airline industry to improve cabin air quality

As 13 Investigates first reported in 2018 , the problem stems from how some airplanes are designed. Aircraft use "bleed air" systems where fresh air enters jet engines, some ble

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