What is known about Xi Jinping's 'special plane'?

Chinese President Xi Jinping travelled to US in a heavily modified Air China Boeing 747-8 Intercontinental, which Chinese media refer to as zhuan ji, or 'special plane'. The plane is drawn from Air China's fleet and is reportedly the last passenger variant of the 747 ever built. The aircraft reportedly also has threat-detection systems, missile-defence countermeasures with VIP interior.