IEC 62396-5:2014(E) provides a more precise definition of the threat that thermal neutrons pose to avionics as a second mechanism for inducing single event upset (SEU) in microelectronics. IEC 62396-5 addresses two main items: - a detailed evaluation of the existing literature on measurements of the thermal flux inside of airliners, and - an enhanced compilation of the thermal neutron SEU cross-section in currently available SRAM devices (more than 20 different devices). The net result of the reviews of these two different sets of data will be two ratios that are considered to be very important for leading to the ultimate objective of determining how large a threat is. This new edition includes the following technical changes with respect to the previous technical specification: document upgraded to an IEC international standard, change to title, updated references and bibliography, consideration of smaller geometries, addition of recent data on neutron cross-sections, etc.