Final answer:
The deployment bag of a parachute is held in place during deployment by a timing mechanism that relies on pilot chutes, static lines, and deployment sequencing to ensure that 3/4 of the canopy deploys before the bag is released.
Step-by-step explanation:
The question refers to the deployment system of a parachute, specifically one with an automatic activation device for a back-mounted parachute. When a parachute deploys, the bag which contains the parachute, known as the deployment bag or 'D-bag,' is designed to stay within the pack until a certain stage of the deployment is reached. This is to ensure that the canopy has enough time and space to inflate partially and stabilize before the entire system is fully deployed. The mechanism that keeps the deployment bag in the pack until 3/4 of the canopy has deployed usually involves a combination of pilot chutes, static lines, and deployment sequencing that is carefully timed so that the bag is released at the appropriate moment in the deployment sequence. Pilot chutes play a crucial role by creating drag and pulling the deployment bag out, but only after a certain amount of canopy has unfolded.