ΔE 15.1, loose: different enough that you should pick on purpose. USAF Light Blue is a little lighter, more muted, cooler than Turquois (Phthalo).
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). USAF Light Blue is a little lighter, more muted, cooler than Turquois (Phthalo).
The same difference applies the other way round: Turquois (Phthalo) is a little darker, more saturated, warmer.
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 Turquois (Phthalo) on the colour wheel See USAF Light Blue on the colour wheel
All matches: Turquois (Phthalo) equivalents · USAF Light Blue equivalents