A method of operating a drilling system includes suspending a tubular drill string from a travelling assembly into an opening on a drill floor, operating a sensor to measure and to provide a first signal, providing a second signal, and comparing the first signal with the second signal. The travelling assembly is a part of a hoisting system. The first signal represents an acceleration or a velocity of the tubular drill string in a direction into or a direction out of the opening. The second signal represents an operational parameter of the hoisting system. The operational parameter is indicative of a vertical speed or of a vertical acceleration of the travelling assembly.