Core Viewpoint - Delta Airlines is replacing engine units on over 300 Airbus aircraft to address toxic gas leak issues in the cabin air, which have been increasingly reported in recent years [1][3]. Group 1: Toxic Gas Leak Issues - There has been a rising frequency of toxic smoke incidents in commercial aircraft cabins, posing a hidden risk that has led to brain damage in some passengers and crew members [3]. - Since 2010, the Federal Aviation Administration (FAA) has recorded thousands of reports related to toxic gas leaks, with a significant increase in recent years, particularly concerning the Airbus A320 series aircraft [3].