I don't think Delta cares if you have a few failures in the first few years of your training. What they DO care about is honesty. Don't try to sugarcoat anything in your interview. Be 100% honest, if they catch you lying they will show you the door and never let you come back. They would rather see you own your mistake and find out what you learned from it. As long as you have a "reason" and not an "excuse" you should be OK.