Simplify the following text for a Grade 6 native English-speaking person.
Original: The first order was placed in October 1995 ; McDonnell Douglas and Boeing merged in 1997 prior to production , and the first planes entered service in 1999 as the Boeing 717 .
Simplified: McDonnell Douglas merged with Boeing in 1997 , so the plane was renamed the 717 . The Boeing 717 started to fly passengers in 1999 .