sentences:  Such procedures are used to allow aircraft to land and take off when instrument meteorological conditions (IMC) impose instrument flight rules (IFR).The Flight Safety section of International Civil Aviation Organization (ICAO) is responsible for PANS-OPS, which outlines the principles for airspace protection and procedure design to which all ICAO signatory states must adhere.The regulatory material surrounding PANS-OPS may vary from country to country.