Altitude and latitude variations in avionics SEU and atmospheric neutron flux

The direct cause of single event upsets (SEUs) in static random-access memories (SRAMs) at aircraft altitudes by atmospheric neutrons has been documented previously. The variation of the in-flight SEU rate with latitude is demonstrated by new data over a wide range of geographical locations. Measurements and models of the atmospheric neutron flux are also evaluated to characterize its variation with altitude, latitude, and solar activity. The data confirm the validity of the initial conclusions of A. Taber and E. Normand (1993) regarding the cause/effect relationship between the atmospheric neutron flux and the measured SEU rate. The Wilson-Nealy atmospheric neutron model allows solar activity variations to be accounted for and is also more accurate in representing the nonseparable relationship between altitude and latitude variations