Landing is usually the worst part of the flight. It's the most difficult one too! The scenario that we are describing here is when the craft has a problem and it is difficult to land or there isn't much time to land safely on your own.
To avoid crash landings, quadcopters can be equipped with parachutes. The APM flight controller has an option of adding a parachute. The hardware mechanism of a parachute must be connected via servo wire to the flight controller and the trigger must be configured through the software.
Parachutes have a very simple way of activating. The bottom side of the parachute is open and the idea is that while the quadcopter is flying, the air goes from the bottom side and waits. As soon as we trigger the parachute, the top side will open and the parachute will fill with air, slowing the craft enough for a safe landing.