According to Hyundai, the UAM sector is expected to grow to $1.5 trillion within the next 20 years. But Hyundai is far from the first to announce UAM plans. Uber is working on a flying taxi with Bell. Volocopter has an 18-rotor autonomous air taxi. Lilium’s flying taxi may carry as many as five passengers, and Boeing and Kitty Hawk have teamed up on their own venture.