ΔE 17.5, loose: different enough that you should pick on purpose. Light Aircraft Gray BS381C/627 is much more saturated than Administratum Grey.
Can I use Light Aircraft Gray BS381C/627 instead of Administratum Grey?
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Light Aircraft Gray BS381C/627 is much more saturated than Administratum Grey.
Can I use Administratum Grey instead of Light Aircraft Gray BS381C/627?
The same difference applies the other way round: Administratum Grey is much more muted.
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.