I have recently come back from a holiday to Central America via transiting through America and I would like to share my experience with you.
1. You need a Visa Waiver Program (VWP) and Electronic System for Travel Authorisation ( ESTA) to transit through America, even if you are not leaving the airport. You need to apply for this online 72 hours prior to travel. Costs USD $14.00. The site is www.cbp.gov/esta. Mistake number 1: I booked my tickets online with Delta Airlines, as I was transiting, I didn't realise that I needed a VWP and ESTA until the night before when I was checking in online. (There was no information on the website). I applied for the VWP and ESTA and printed off the receipt. There were problems at checkin at Sydney Airport, but I had my receipt and I was able to get onto the plane.
2. Booking through Delta Airlines I had a transiting period of approx. 2 hours at LAX airport for my connecting flight to Central America. Other countries I have visited around the world, that is plenty of time to make the next flight, so I wasn't concerned when I booked my flight. Mistake number 2: If you are transiting through America allow up to 3 hours to get through immigration/customs. It is a nightmare. It took me 1 1/2 hours to get through immigration. It is so slow, you have to be fingerprinted, machines don't work etc. Next you have to pick your bags up from the carrousel and take them to another check in counter. ( Very frustrating). Then you have to wait in line again to go through customs, again very slow, as everybody has to take off shoes, jackets, belts etc.( People should wear slip on shoes to get through faster). Once through customs it was the dash to the plane, thank goodness it was close by and I reached the plane with 5 minutes to go. Unfortunately, other passengers weren't so lucky, about 7 passengers did not make the flight. The airline knew they were coming through customs, but could not wait and flew off with out them.
3. It was the same coming back into America, this time through Atlanta. It was even worse, as this is the major hub for Delta Airlines. Again it was a nightmare. But this time I had 1 1/2 hours to get through. Thank god for some kind people who let me push my way through customs and I managed to the reach the plane as they were closing the doors and they let me on. Again, over a dozen people did not make the flight, but this time they did wait 15 minutes for them, but they just didn't make it.
I am a relatively fit person and running through an airport, like a mad women is not a good look. It did add a lot of stress to my trip that was otherwise fantastic. Please check your transiting times and if they are under 3 hours, change your flights, it is not worth the hassle.
I had no problems flying with Delta Airlines, the flights were good and the planes comfortable, they just need to change their transiting times, as I know my experience is not an isolated case.