On Sept. 11, the nation’s aviation system quickly and safely almost 4,500 planes that were in the air when the terrorist attacks took place. How was this (S1)_____? What was it like inside air traffic control centers and at airline (S2)_____? How was the decision made to land all the planes? And how did controllers execute it?

Some USA TODAY reporters spent seven months (S3)_____ more than 100 people involved in key decisions that day. The reporters traveled to New York, Washington, Chicago, Texas and Atlanta.

The (S4)_____, thoughts and quotes in the stories are based on interviews with (S5)_____ or with sources who had (S6)_____ to tape recordings. Accounts of the day’s events were (S7)_____. (S8)_____________________________________________________________________.

(S9)____________________________________. A key source was the FAA radar data from the Traffic Situation Display. The system tracks all aircraft in the United States and Canada that have filed flight plans: (S10)__________________________________. It also estimates the location of planes over the Atlantic and Pacific oceans flying to the and from North America.

(S1) accomplished

(S2) headquarters

(S3) interviewing

(S4) scenes

(S5) participants

(S6) access

(S7) verified

(S8) Reporters and editors also scrutinized hundreds of pages of records, including transcripts of radio calls with the four hijacked jets and a long kept by the Federal Aviation Administration.

(S9) USA TODAY compiled and analyzed data from several sources.

(S10) commercial jets, private planes, cargo jets and military aircraft.