United Airlines on July 27 will begin maximizing airflow volumes through its filtration systems during boarding and deplaning on all mainline aircraft. The carrier's high-efficiency particulate air filtration system recirculates air in the cabin every two or three minutes and removes 99.97 percent of airborne particles, including viruses and bacteria, according to United. The carrier decided on the new policy during a review of procedures with partners Clorox and the Cleveland Clinic.