Delta airlines have a poorer record. Delta said it has been aggressively retiring inefficient planes, such as 8 DC9s (average age: 38 years) that will be parked this year. In addition, the airline says its mpg is impacted by having one of the industry’s highest passenger and cargo load factors, which results in heavier aircraft, and having a high percentage of short fights. In addition, Delta has a significant presence on the East Coast, where delays are more frequent.
What does "Delta said it has been aggressively retiring inefficient planes ... that will be parked this year" mean (in particular, the words "aggressively" and "park")?