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 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 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 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 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 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 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 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 within a predetermined period of time from starting the timer. <EOS>