I'll add my vote to Dan's pick as one of my favorites --
No Parachute by
Arthur Gould Lee
And a few others --
Sopwith Scout 7309 by Sir Gordon Taylor
The Spider Web by T. D. Hallam (flying boats, not scouts, but I could not put it down once I started reading it)
Red Baron, The Life And Death Of An Ace by Peter Kilduff
Malaula! The Battle Cry Of Jasta 17 by
Julius Buckler, Edited by Norman Franks from a translation by Adam Wait
The Balloonatics by Alan Morris (OK, balloons not aeroplanes, observers not pilots, but still a great read!)