Perhaps you should try some spelling variations:
significant navigation » significant variation (Expand Search), significant deviation (Expand Search), significant variations (Expand Search)
navigation data » validation data (Expand Search), navigation task (Expand Search), calibration data (Expand Search)
mean decrease » a decrease (Expand Search)
gap decrease » a decrease (Expand Search), gain decreased (Expand Search), step decrease (Expand Search)

You may be able to get more results by adjusting your search query.

• The words AND, OR and NOT may confuse the search; try adding quotes: "(( significant ((gap decrease) OR (mean decrease)) ) OR ( significant navigation data ))~".
• Adding a wildcard symbol may retrieve word variants: (( significant ((gap decrease) OR (mean decrease)) ) OR ( significant navigation data ))*.