http://www.spaceadventures.com/zerog/index.html
For over 30 years, NASA and the Russian Space Agency have trained their astronauts and cosmonauts using parabolic-flight aircraft. Now, this same zero-gravity training is available to you.
Weightlessness is achieved by having an aircraft -- in our case a Russian Ilyushin-76 -- start from level flight, and pitch up to approximately 45 degrees nose-high and wings-level. As the plane flies upward, it accelerates itself and everyone inside.
Then, the engines are powered back and the airplane glides over the top of the arch with just enough power (jet thrust) to overcome air friction and drag. Everyone inside the airplane then experiences the sensation of "free-fall". The body of the aircraft acts as a shield to prevent the passengers inside from experiencing the drag of the atmosphere. Passengers sustain approximately 28-30 seconds of microgravity during the pushover, which continues until the aircraft is about 30 degrees nose down.
The aircraft is then slowly pulled out of the dive, and when all people are safely on the padded floor, the acceleration is increased to about 1.8 g's, for the pull-up to 45 degrees nose-high, and the maneuver is repeated. The maneuver requires a block of airspace from about 25,000 to about 35,000 feet. There are usually 8 to 12 maneuvers in one flight