11.  A fourth plane crashed in the Pennsylvania countryside after doomed passengers apparently struggled with the hijackers.

12.  A fourth plane hijacked days later was also diverted to Jordan.

13.  A fourth plane crashed into a Pennsylvania field.

14.  A fourth plane crashed into a Pennsylvanian field.

15.  A fourth plane crashed in Pennsylvania.

16.  But it was the fourth plane to be hit in six days, and caused the United Nations to suspend both humanitarian and operational flights for the day.

17.  But it was the fourth plane to be hit in six days, and caused the United Nations to suspend both humanitarian and operational flights.

18.  It was the fourth military plane shot down by the rebels this year.

19.  It was the fourth military plane to be shot down by the rebels this year.

20.  It was the fourth aid plane to fly to Termez.