The Maneuvering Characteristics Augmentation System (MCAS) is a flight stabilizing feature developed by Boeing that became notorious for its role in two fatal accidents of the 737 MAX, which killed all 346 passengers and crew on both flights. A first MCAS design was implemented on the Boeing KC-46 Pegasus military air tanker. The KC-46, which is based on the Boeing 767, requires MCAS because the weight and balance shifts when the tanker redistributes and offloads fuel. It allows pilots to assume control of the aircraft.