just relax....
4 weeks is a norm right now! no reason to call, email, tweet, or whatever everyone does these days...
As long as you have a stable job for now, just focus on what you have and let the cards fall where they may, you just might come across the wrong way if you keep bugging hr!
If you don't have a stable job, then I suggest going to a gum to take out your frestrations and anxiety!
depending on what you applied for (FTSO, FO, CAPT), you will have a wait time from 4 weeks to 2 months in between each response and the joiniong date could be 6 -10 months from the time of your interview.
good luck, but as a rule, good news travels slow, so you probably did good in the selection process!