Not sure about the Garbage (better word than Sh*t seeing as how sensitive Navs are). Since Navs disappeared from civilian airliners in the 70s and engineers too for that matter the number of incidents/accidents attributable to the software is minor in comparison to the number of flights without Navs/Flt Engs.
So should we still be carrying these chaps? How much do Navs cost the RAF each year? And the Navy too?