A mates son from WA is travelling from Seattle to Sydney, via LAX. His itin is as follows:

Leave: December 07, 2005
United Airlines 703
Depart 07:00 PM Seattle - Tacoma Intl.,(SEA)
Arrive 09:30 PM Los Angeles Intl.,(LAX)
United Airlines 839
Depart 10:25 PM Los Angeles Intl.,(LAX)
Arrive 08:05 AM Sydney Kingsford Smith,(SYD)

I have suggested that he might consider changing to the first leg of his trip to a 5pm departure from SEA to LAX, simply because it only him 55 mins from the time he arrives at LAX to 10.25pm when his international flight departs. Even if he makes the flight I suggested to pack enough clothes in his carry on to last him a couple of days because I don't like his chances of his luggage being on the same flight. He has to speak with the TA again tomorrow. I suspect from the booking that he will clear customs, immigration and security in SEA and won't have to do it again in LAX which will save him heaps of time.

Apart from having problems if his domestic leg from SEA-LAX is delayed, what would be a good estimate of time for a pax to transfer at LAX.

I honestly don't see this as being a problem. The two flights should both arrive and depart out of the same terminal (T7) and one hour is more than enough time for him (and his luggage) to make it to the other gate.

There's no clearing customs or immigration when leaving the U.S. (That's why international departures don't have to use the Tom Bradley International Terminal, though those of airlines that fly only internationally from LAX, such as Qantas, do anyhow if they have no gates anywhere else.) The check-in agent at SEA will make sure his passport is in order. This will probably be repeated once or twice more, since UA doesn't want to have to fly him back at its own expense if Australia won't let him in. That doesn't add more than a few seconds to the process, since the people who will look at his passport would generally have to see some sort of ID anyhow.

As for security: he'll clear it in SEA and will stay airside at LAX so he won't have to clear it again there. That's a real time-saver.

55 minutes is plenty of time to connect. I would only worry if his flight arrived late and he had less than 20 minutes to get to the SYD flight.

Thank you for your replies. I phoned him today and put his mind at ease. Thanks again.

Make sure he has his visa!!

If he's a U.S. citizen, he'll have an electronic entry authorization stored in the Australian immigration service's computers. Nothing in the passport. However, he should still be sure to get it before he leaves. Airlines/travel agents often take care of it. If his doesn't, he can get it on the Web in minutes for (IIRC) A$20.