The Configurable Scanning Submillimeter-wave Instrument/Radiometer (CoSSIR) ALOFT dataset consists of data measured onboard the NASA ER-2 aircraft during the Airborne Lightning Observatory for Fly’s Eye Geostationary Lightning Mapper Simulator and Terrestrial Gamma-ray Flashes (ALOFT) field campaign. ALOFT aimed to study terrestrial gamma-ray flashes (TGFs) and gamma-ray glows in thunderstorms and to validate observations from the International Space Station Lightning Imaging Sensor (ISS LIS) and the Geostationary Lightning Mapper (GLM). CoSSIR data are available from June 15, 2023 through July 29, 2023, in netCDF-4 format.