IEC TS 62396-5:2008 (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. Addresses more in detail the following: detailed evaluation of the existing literature on measurements of the thermal flux inside of airliners; an enhanced compilation of the thermal neutron SEU cross section in currently available SRAM devices (more than 20 different devices).