Crash of two 737 aircraft puts flight-control system in the spotlight

An Ethiopian Airlines 737 Max that crashed on Sunday was fitted with a system called MCAS, or Maneuvering Characteristics Augmentation System. MCAS is intended to help prevent a stall, but could surprise pilots unfamiliar with its action of lowering the plane's nose. A Lion Air 737 that crashed in October was also fitted with MCAS.