ΔE 9.5, close: similar, with a visible difference side by side. Light Blue RLM65 is a little lighter, more muted than Light Aircraft Gray BS381C/627.
Usually, if you are not matching paint already on the model. Close match (ΔE 9). Light Blue RLM65 is a little lighter, more muted than Light Aircraft Gray BS381C/627.
The same difference applies the other way round: Light Aircraft Gray BS381C/627 is a little darker, more saturated.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Light Aircraft Gray BS381C/627 on the colour wheel See Light Blue RLM65 on the colour wheel
All matches: Light Aircraft Gray BS381C/627 equivalents · Light Blue RLM65 equivalents