If the quadcopter started its fall in a normal attitude, all four of the propellers will rotate reverse of its normal direction. The now spinning props will actually act as something of an air ...

There are significant benefits to using engines that rotate in the same direction. The first is a lower cost of maintenance.

The problem becomes one of propellers. Standard propellers are designed to create thrust in one direction only. Every quadcopter uses two clockwise rotation and two counterclockwise rotation ...