A method of controlling an elevator system, wherein the elevator system comprises: a hoistway; at least one elevator car configured for moving along the hoistway; at least one positional sensor (24, 26, 63, 83, 93) arranged at a defined position within the hoistway; and a speed and/or acceleration sensor configured for determining the current speed and/or acceleration of the at least one elevator car within the hoistway; and wherein the method comprises the steps of: a) determining the current speed and/or acceleration of the at least one elevator car within the hoistway and providing speed and/or acceleration information; b) calculating current positional information of the at least one elevator car within the hoistway from the provided speed and/or acceleration information; c) checking the validity of the speed and/or acceleration information; d) in case the speed and/or acceleration information is determined as being valid: operating the elevator system based on the calculated positional information; e) in case the speed and/or acceleration information is determined as not being valid: e1) starting a timer; e2) controlling the at least one elevator car to run by the at least one positional sensor (24, 26, 63, 83, 93) for re-calibrating the positional information of the at least one elevator car; and e3) stopping any operation of the elevator system, in case the at least one elevator car has not run by the at least one positional sensor (24, 26, 63, 83, 93) within a predetermined period of time from starting the timer. a hoistway; at least one elevator car configured for moving along the hoistway; at least one positional sensor (24, 26, 63, 83, 93) arranged at a defined position within the hoistway; and a speed and/or acceleration sensor configured for determining the current speed and/or acceleration of the at least one elevator car within the hoistway; a) determining the current speed and/or acceleration of the at least one elevator car within the hoistway and providing speed and/or acceleration information; b) calculating current positional information of the at least one elevator car within the hoistway from the provided speed and/or acceleration information; c) checking the validity of the speed and/or acceleration information; d) in case the speed and/or acceleration information is determined as being valid: operating the elevator system based on the calculated positional information; e) in case the speed and/or acceleration information is determined as not being valid: e1) starting a timer; e2) controlling the at least one elevator car to run by the at least one positional sensor (24, 26, 63, 83, 93) for re-calibrating the positional information of the at least one elevator car; and e3) stopping any operation of the elevator system, in case the at least one elevator car has not run by the at least one positional sensor (24, 26, 63, 83, 93) within a predetermined period of time from starting the timer. e1) starting a timer; e2) controlling the at least one elevator car to run by the at least one positional sensor (24, 26, 63, 83, 93) for re-calibrating the positional information of the at least one elevator car; and e3) stopping any operation of the elevator system, in case the at least one elevator car has not run by the at least one positional sensor (24, 26, 63, 83, 93) within a predetermined period of time from starting the timer.