Emergency bi-fold door closing prevention system

A bi-fold door safety braking system comprising:

• a building wall having an access opening therein for accommodating a plane, the access opening having an upper edge and a pair of lateral edges;
• a bi-fold door being hingedly mounted to the building wall, the bi-fold door including a plurality of panels each being laterally elongated, the panels being hingedly coupled together and being foldable with respect to each other, the plurality of panels including a bottom panel having a bottom edge, the bottom edge configured to be positioned adjacent to a floor surface to define a closed position and being positioned adjacent to the upper edge to define an open position;
• and
• a safety line assembly being attached directly to the building wall and extending between the building wall adjacent to the upper edge and the bi-fold door adjacent to the bottom edge, the safety line assembly having an extendable length, the length of the safety line assembly being extendable when the bi-fold door moves toward the closed position below a threshold velocity, the length of the safety line assembly being inhibited from extending when the bi-fold door moves toward the closed position above the threshold velocity to prevent unimpeded falling of the bi-fold door.