The band Toto were originally intended to perform the track, but legal conflicts between the producers of Top Gun and the band's lawyers prevented this.
Bryan Adams was approached to allow his song "Only the Strong Survive" on the soundtrack and perform "Danger Zone", but Adams refused any involvement, feeling that the film glorified war and he did not want any of his work linked to it.
REO Speedwagon were also approached to perform "Danger Zone", but the group declined due to not being allowed to contribute any of their own compositions to the soundtrack.
Eventually, the film producers agreed that "Danger Zone" would be recorded and performed by Kenny Loggins.
http://en.wikipedia.org/wiki/Danger_Zone_(song)
