Dancetheblues - if you like monitoring planes, you'd love the app my DS (18, narrowly missed selection for air traffic control training recently) has on his iphone. No idea what its called, but it tells him not only where the plane is going, but also where it came from, who operates it, the type of plane and how many passengers are on it! We recently went to Europe on tunnel, he loved telling us where planes above us around Heathrow/Gatwick were going to, plus lots that went above us in Europe!!
Op - I would second using flight radar24, put the flight no in and you will be able to monitor his flight progress each way.
I get why you are nervous, I am similar but learning to chill more as DC get older - you just have to take a deep breath and let them spread their wings. My 2 were abroad separately last summer (age 15 & 17) - DS on a church volunteering trip to S africa, which was especially worrying, and DD on a Guide trip in Europe. Both had a fab time, DS is thinking of going back to S africa one summer, DD just been selected for another guide trip next year!
Hope your DS has a fab time and yes, I second keeping a diary.