Before each flight, it is necessary to check the propellers for cracks, wear, warp, corrosion, and loose screws. If any of these conditions are present, the propellers should be replaced. Follow the instructions in the user manual to replace the propellers. Use the included screwdriver to replace the propellers. Please follow the instructions provided. Remove the two blades and screws from the motor, and replace with the new propellers and screws. Attach the marked propellers to the marked motors, and the unmarked propellers to the unmarked motors. Ensure that the propellers and motors are installed securely before each flight.