Within the Dutch airspace there is a network of navigation beacons that mark the airspace structure, including VHF Omnidirectional Range (VOR), Distance Measuring Equipment (DME) and Non-Directional Beacon (NDB) for the benefit of navigation and guidance of civil air traffic. Besides the beacons that mark the airspace structure, Instrument Landing Systems (ILS) combined with DME are used for accurate landings on almost all civil airports. Furthermore, ATC-NL uses a network of Direction Finders (DF) to assist air traffic controllers. All these aforementioned systems need to be calibrated within the legally established deadlines. The calibration of these systems are partly done by flight inspection which is the scope of this contract. (The ground checks are out of scope of this contract.)