A friend of mine (brand new hire, started training Aug. 6) walked in my resume this past Monday, 8/13. Got a call that same day and set up an interview for next Tuesday, 8/21. I heard they're interviewing for the October class now.
If you're emailing them from a gmail account, it might get blocked. I sent the pilot recruiter an email on Tuesday with a question about the FCC license, and heard nothing back. I called today to follow-up and she said "You know, it might have been blocked by the server, let me check... yeah, here it is. The system bans certain emails, I'm glad you called or else I'd never have seen it."
Give them a call, tell them that you're just following up on your resume.
Even better idea would to be to send your resume in via USPS Priority, with signature confirmation... that way you know that it'll get there and that they'll see it. That's what I'm going to do in the future, I'll only email my resume if it's what they specifically want.