On 29 July 2023, an ATR 72-500 on a scheduled commercial flight climbed in VMC with a target altitude set at FL160 with autopilot engaged and IAS mode. During the climb, the flight was asymmetrical with a sideslip to the left. Passing FL 136, the crew changed the vertical guidance mode from IAS to V/S mode (+300 ft/min). Passing FL 149, an IFSD occurred. The crew managed to recover the upset situation.
