How often was Ash trying to pass for human? There's the moment when he runs on the spot, when the others go to search the planet. As if he's warming up for something. And he only drinks milk at the dining area.
shareFrom what I gather it wasn't typical for an android's identity to be concealed from the crew. So there would be no need to "pass as a human" per se.
This time was the exception.
But it wouldn't appear a difficulty for this android to blend in as if human, as was his assignment in this particular storyline.
If one recalls correctly....
None of the crew even knew ASH was a droid.
While watching the film, you can tell he's up to something. But you don't know what it is until he tries to off Ripley.
Ultimately it makes sense - he is up to something (protecting the alien).
But passing for human? It wasn't necessary as the crew already thought he was human.
i think there was a deleted scene where Lambert asks Ripley if she ever got sexual with Ash because he seemed pretty odd, maybe gay.
also Ash was a replacement science officer on-board (for obvious reasons) so he always appeared like an outsider.