I've taken a complete m-atx system, wrapped in a towel for a bit of protection, and lobbed in my suitcase before 13 hour flight to Malaysia too (That's where I'm living for a while)
Almost every flight I take (maybe 20+ a year) I have laptop and mobile HDD with me too.
Totally not an issue.
Out of literally tons of flights I think I have been asked once to switch on the lappy, thats' it.