Going the distance: Aircraft and lightning, how far is far enough?

Abstract

With the limited data that is available this document serves the purpose to illustrate why aircraft should remain 25 nautical miles (NM) away from thunderstorms. There has been no extensive research on aircraft flying in or near thunderstorms since the 1980s, so data presented is from just normal naturally occurring lightning strikes. The studies show that 95-99% of all lightning strikes are within a 10 NM range; however, while uncommon, there are lightning strikes that can range from 20 to 30 NM [1][2]. Most aircraft agencies stress a 20 to 25 NM distance from thunderstorms. Finally in this paper we take a look at probability and risk estimations for an aircraft being struck by lightning and at what distances from storms is an acceptable level of risk reached. From the risk analysis of the two test cases we can see there are instances that indicate an acceptable level of risk within 25 NM, however it is not until then that a satisfactory level is reached across the board. Because of the studies and the risk assessment provided it seems reasonable why most pilots and aircraft agencies stress a 20 to 25 NM limit for avoiding thunderstorms.