ABSTRACTA methodology to determine the required navigation performance (RNP) for aircraft precision approach and landing under instrument meteorological conditions (IMC) is described. The RNP in turn defines an aircraft containment surface about the nominal flight path, called a tunnel, which specifies the allowed approach and landing flight path limits. If the aircraft and its navigation system satisfy the RNP, then the aircraft will successfully traverse the tunnel, terminating in a safe landing. The tunnel is defined by four RNP parameters: accuracy, integrity, continuity, and availability.