He hooked up the flux capacitor and time circuits of the steam time car to a parachute that was stored inside its storage compartment, along with a hot air balloon. He then planned to don a diving suit to protect his body from the rigors of space-time and the temperature variation.
A person would ascend in the balloon to a distance of half a mile, and then would be released from the balloon. The person would fall at a rate of 35 feet per second per second, and would reach 88 mph between four and five seconds. Since the time circuits and flux capacitor are connected to the parachute, the person would travel through time. The time traveler would then pull the ripcord of the parachute once they traveled through time, and arrive safely on the ground in that time period.
The first successful test of the time parachute took place in 1986 by Doc Brown, wearing the diving suit, and Marty McFly, wearing a radiation suit. They traveled from 1986 to 2035 in the Lone Pine Mall parking lot.
Later, after having been chased to Doc's second lab by Griff Tannen, Doc attempted to combine the time circuits from the time parachute with the gliderboard they had stolen. However, after discovering that the gliderboard was broken, he used the temporal field generator Mk II to escape back to 1986, where he used the time circuits to complete the newer, unfinished DeLorean time machine.