Using double has enough precision for accurate lat/lon down to inches for 6-7 decimal places. In aviation, if decimal degrees are used, they typically go to at least 7 decimal places. In our NASA simulations, lat/lon data are doubles while all other attitude and altitude are floats. In other words, the 6th decimal place for altitude isn’t significant while the 6th decimal place for lat/lon is for sub-foot accuracy. You should not use float for lat/lon if you need precision down to sub-feet.
You can play around in Google Earth to see what accuracy you get by placing markers and manipulating the last decimal digit.