I try to persuade skill test candidates to use Sky Demon for planning purposes but in the air I want to see basic Mark 1 eyeball and a map, navigation. The fatal accident(pilot) to GBXRG off Guernsey in 2011 was a result on just relying on GPS with no realistic back up plan based on simple DR navigation. Due to this accident I always cover alternator failure on the test too. For GA light aircraft flying I believe that GPS enhances basic DR navigation but it shouldn’t be seen as a total replacement.