The BGR helicopter (Sikorsky S-76B) is used for airborne geophysical surveying of the Earth’s subsurface. The standard equipment comprises the methods electromagnetics, magnetics and radiometrics. The passive helicopter-borne radiometric (HRD) measuring system is a gamma-ray spectrometer, which is installed into the helicopter. The detector of the spectrometer consists of five Sodium-iodide crystals (volume: 4 l per NaI crystal). The spectral range of gamma radiation recorded ranges from 0 to 3 MeV. The results are displayed as total count rate and the (equivalent) concentrations of Thorium, Uranium and Sodium as well as the exposure rate at ground level.