There are 2 books in the Chickenhawk series. The newest book is Back in the World which came out in 1993.

1
Chickenhawk

Book cover of Chickenhawk
A true, bestselling story from the battlefield that faithfully portrays the horror, the madness, and the trauma of the Vietnam War
 
More than half a million copies of Chickenhawk have been sold since it was first published in 1983. Now with a new afterword by the author and photographs taken…
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2
Back in the World

Back in the World
The sequel to the best-selling Chickenhawk continues the Vietnam helicopter pilot's story after he returns home, as he descends into panic, alcoholism, and drug smuggling; serves time in prison; and finds gradual personal healing. 50,000 first printing.