Development formally started in the late-1990s with an online proposal and code being written in 1996, but using custom 3D graphics code. Development of an OpenGL based version was spearheaded by Curtis Olsen starting in 1997, after the initial start in 1996. A large community response lead to many contributing to the project from its start in late '90s up to the present.
Rather than start entirely from scratch, FlightGear developers made use of the LaRCsim flight model from NASA, with OpenGL for 3D graphic code, and freely available elevation data. First working binaries came out in 1997, with an intense updating of newer versions for several years resulting in progressively more stable and advanced programs.
Versions 0.7–0.9 (2001–2003)
By 2001, the team was releasing new beta versions regularly (0.7.x, 0.8.0, over 2001-2003) and with 0.9.xx (2003-2006). Later in the decade, the rate of final public releases slowed, but had larger amounts of content (0.9.10, 1.0.0 etc.). The maturity of software by 2005 lead to more widespread reviews, and increased popularity.
Version 0.9.0-0.9.11 (2002-2007)
The use of version numbers slowed dramatically after the late 2002 release of version 0.9.0. Versions 0.9.9 (2005) and 0.9.10 (2006) had about 8 all-new or redone aircraft adding to a total of 70-90 aircraft. FlightGear 0.9.10 won Softpedia's "Pick" award (5 out of 5 stars) on June 3, 2006 as well as the "100% CLEAN" Softpedia award.
Behind the scenes there was a 0.9.11-pre1 released in 2007 that ended up being superseded by FlightGear 1.0. The pre-version had about 33 new or redone aircraft.
Version 1.0 (2008)
The version number marked a formal transition out of beta development since software's first release in 1997, ten years prior.
Version 1.9.0 (2008)
At the time version 1.9.0 was released FlightGear switched from PLIB to OSG, which caused the temporarily lost of some of the features like 3D clouds and shadows. On the contrary new features such as particles add another degree of realism to the simulation. Most aircraft developed for OSG do not work with older versions. The users is able to choose out of 230 aircraft provided with 1.9.0, altough only a few are included in the base package.
Final build code release dates by year.