Described herein are methods and systems for detecting and correcting errors when picking up and lowering a payload coupled to a tether of a winch system arranged on an unmanned aerial vehicle (UAV). For example, the winch system may include a motor for winding and unwinding the tether from a spool, and the UAV's control system may control the motor to lower the tether and monitor an electric current supplied to the motor to determine whether a payload has detached from the tether. This process of lowering the tether and monitoring the motor current may be repeated up to a predetermined number of times, at which point the control system may operate the motor to detach the tether from the spool, leaving both the tether and the payload behind.