Old-fashioned walkthroughs (in written form, not playthrough videos) for all three games can be found here:

http://adventuredoor.net/walkthroughs/pilot-brothers-walkthrough/
http://adventuredoor.net/walkthroughs/pilot-brothers-2-walkthrough/
http://adventuredoor.net/walkthroughs/pilot-brothers-3-back-side-earth-walkthrough/

These are complete walkthroughs for international versions of these games, with the exception of the third game they should also work with the original Russian versions.

Since the games have hint buttons, video buttons, and even skip buttons in some puzzles, it's kind of unlikely that someone would desperately need these walkthroughs, but still having said that, I think these are the very first complete walkthroughs written in English for these games (but don't quote me on that!).

These are probably most useful for "traditional" adventurers who prefer written instructions, but they also contain information that playthrough videos don't usually cover, such as the solution for fridge padlock puzzle explained etc.

Thanks! Quite helpful and – indeed – written walkthroughs are the best ones! :)