Some embodiments relate to a manned vertical take-off and landing (VTOL) aerial vehicle (AV) and to methods relating to such VTOL AVs. An example vehicle comprises: a body comprising a cockpit; a propulsion system carried by the body to propel the body during flight; pilot-operable controls accessible from the cockpit; a sensing system configured to generate sensor data associated with a region around the manned VTOL AV; a control system configured to enable control of the manned VTOL AV to be shared between a pilot and an autonomous piloting system, wherein the control system may utilise the sensor data; and a three-dimensional model of the region; and program instructions to: determine a state estimate and a state estimate confidence metric; generate a three-dimensional point cloud of the region; generate a plurality of virtual particles within the three-dimensional model; compute a plurality of scores, each score being associated with one of the plurality of virtual particles; and update the state estimate based at least in part on the computed scores, thereby determining an updated state estimate.