The act of falling before a personal fall arrest system begins to apply force to arrest the fall.
Merriam-Webster Online Dictionary
free fall (noun)1.
the condition of unrestrained motion in a gravitational field , also such motion
2.
a) the part of a parachute jump before the parachute opens
b) a rapid and continuing drop or decline - a free fall in stock prices
uncontrolled descent, rapid drop, sudden decline, steep plunge, swift fall