Wow, when you loose lift you come down fast! Are the areas of lift pretty well defined where you sail? Or does it vary considerably? Your son was talking about hitting the turnpoint? Also what is the handheld device with the tone? Those close calls your son had were pretty heart stopping! It does look like fun but I would be looking at those strings and clips and freaking out!
Jim
There can be areas of lift or sink sometimes in the exact same place but at a different moment in time. It varies based on a huge number of variables that are mostly invisible.
Turnpoints are locations you must come into a defined proximity to, in the defined order, to complete the task of a competition. See PWC videos for more competition type flying.
The beepy thing is a vario. It gives you and audio representation of your rising or sinking in an air mass. Beep...beep...beep... is nice. It means you are rising slightly.
Beep.beep.beep.BEEEEEEEEEEP means you are rising quickly. This can be as fast as 10 meters per second in very strong thermal conditions.
BAAAAAAAAAAAAAAHHH means you are sinking rapidly. +3 m/sec thermals are usually quite nice. +5 to +6 m/sec are about my limit for strength of thermals to fly in.
Where ever there is rising air there must be sinking air nearby to fill in the vacuum left behind. Going from +6 to -3 at the edge of a thermal can be very rough and cause your paraglider to collapse.
This is quite scary for newbies. Your paraglider is designed to reinflate and fly again if you just put your hands up and let the wing fly at trim speed. Continuing to pull on the brakes and not let the wing regain flying speed is the cause of most cascading collapse events. Advanced design racing wings often need precise pilot input on the brakes to cause them to regain their flying configuration.
Beginner wings will fix themselves every time if you just put your hands up and not pull on the brakes. Still scares the crap out of you until you have the experience and confidence in your gear to know that it will fly if you do what it needs to fly.
I rarely if ever look at the strings or wing while flying now. You learn to go by feeling instead of looking. It tells you everything you need to know by the feeling in your hands and on your harness.