I think it might be close to Lexikos, originally by Letraset now ITC
http://www.myfonts.com/fonts/itc/lexikos/

I think that's it, many thanks!

Can you tell us how big these letters are, where they are located, and if possible, how long ago they were done?

If this sample is on an airplane hangar, I doubt it's a font, in the sense of belonging to a set of letters you can install on your computer and use in a design/layout program. Lettering on buildings is often painted by hand, either because the letters are too big to render any other way, or because they're on a surface that's only accessible to a human on a scaffold. When letters are painted this way, the painter often uses improvised or simplified letterforms rather than precisely rendered copies of a commercially-available alphabet.

You will note Victor I said Lexikos is close as a font but I believe you are correct about the original being hand lettered and thus not a font. Many sign painters produced paper templates of the letter forms that they used as guides through pouncing.

Hello again, I'm not sure about exact dimensions (I'm working on a simulation software, not on the actual aerodrome) but I'd say the square is about 1,70m high by 0,80m wide. Have a look

Also you can see H3 on this one

Lexikos seems close enough to me, the 4 is certainly wider on the photos, and the 3 terminates in a different way, but I can live with this approximation.