See,, weightlessness is caused nly when the body is falling towards the ground with an accleration equal to "g" at that region... this can be explained using NEWTON'S inertial n non inertial frame of references nd relative velocity.... in a parabolic arc trajectory..... weightlessness is experienced during the decent of the object only... that is when it is tracing the descending loop........
Weightlessness is simply due to the absence of reaction force.
Operating principles in case of parabolic flight path
The aircraft gives its occupants the sensation of weightlessness by following an (approximately parabolic) elliptic flight path relative to the center of the Earth. While following this path, the aircraft and its payload are in free fall at certain points of its flight path. The aircraft is used in this way to demonstrate to astronauts what it is like to orbit the Earth. During this time the aircraft does not exert any ground reaction force on its contents, causing the sensation of weightlessness.
Initially the aircraft climbs with a pitch angle of 45 degrees. The sensation of weightlessness is achieved by reducing thrust and lowering the nose to maintain a zero-lift angle of attack. Weightlessness begins while ascending and lasts all the way "up-and-over the hump", until the craft reaches a declined angle of 30 degrees. At this point, the craft is pointed downward at high speed, and must begin to pull back into the nose-up attitude to repeat the maneuver. The forces are then roughly twice that of gravity on the way down, at the bottom, and up again. This lasts all the way until the aircraft is again halfway up its upward trajectory, and the pilot again initiates the zero-g flight path.
This aircraft is used to train astronauts in zero-g maneuvers, giving them about 25 seconds of weightlessness out of 65 seconds of flight in each parabola. During such training the airplane typically flies between 40-60 parabolic maneuvers. In about two thirds of these flights, this motion produces nausea due to airsickness, especially in novices, giving the plane its nickname.