PK (Papa Kilo), this is an international registration for airplanes Indonesia. All countries already have their respective registration. Registration of airplane is usually written on the tail plane. As an example is the registration airlines Boeing 737-200 belonging to Trigana Air Service, which has registered as PK-YRT (picture on left side) or Boeing 737-900 ER lion air owned that has registered PK-LFH. (picture on right side).