By 2007, additional MD-11s and 747-400s had entered service, leading the airline to gradually phase out its oldest aircraft from the fleet. Initially, the Boeing 727 freighters (the oldest and lowest-capacity aircraft) were retired, replaced on routes by Boeing 757 freighters. During 2008 and 2009, the 747-100 and 747-200 aircraft were retired, replaced by the 747-400s and MD-11Fs. In 2009, UPS Airlines retired its entire fleet of DC-8 aircraft; at the time, its 44 aircraft represented nearly half of the active DC-8 fleet flying worldwide.