A question one might ask if one looks into WWII radar or maybe air defense in general. The answer is quite simple, Nicaraguan officials were bribed. Large cargo planes don't just simply disappear and reappear in controlled air space. This may be true for nearly every traumatic civil war. https://en.wikipedia.org/wiki/History_of_Nicaragua_(1979%E2%80%9390) Years of conflict had left 50,000 casualties and $12b of damages in a society of 3.5m people and an annual GNP of $2b. The proportionately equivalent figures for the US would have been 5 million casualties and $25 trillion lost. At least one jet was shot down though: https://en.wikipedia.org/wiki/Corporate_Air_Services_HPF821