Hey Alan,
Do we get a chance to practice in that venue before the event? Not always. Most of the time we rely on two critical portions of every demo in which we perform; 1. Our Outstanding Ground Crew, 2. Former events and monotonous and continued practice. On occasion, if time, weather, and the venue coordinators allow, we will show up a day early and make a practice jump, but that is usually only about 2% to 5% of the time.
The decision to go/nogo is made before anyone leaves the plane. If we go, we all go. If we stay, we all stay as a team. Testing the conditions is accomplished through Ground Crew reports back to the aircraft as well as wind drift indicators and AWOS reports.
We are required to contact ATC at all venues, whether the airspace is highly or mildly restricted.
Demos jumps with flags can be accomplished from any altitude. It all depends on what kind of show you are trying to provide and what your customers need.
Specifically for the San Jose event, we were able to make several jumps into that stadium over the past couple of years, so being familiar with the stadium always helps. As for the airport, they rarely shut down an airport unless we are directly in line with the only active runway. When we jumped into the Marine Corps Marathon next to the Pentagon and Regan International, they did close those runways as we were parachuting in the final approach for those commercial aircraft. you can fin that video on Youtube (Team Fastrax) and see the proximity to the airport. They usually don't stop traffic until just before we exit. So while we were flying around waiting on our exit time, we had heavy traffic above and below us the whole time. ATC makes those calls and coordinated all traffic, including ours, during events where we are in the same airspace. The jump altitude was lower than 6,000 feet AGL.
The roof and cable and wind conditions are always a concern for any demo. Remember that the USPA SIM will explain turbulence and how it can be estimated. Unfortunately, inside a stadium, most of the rules can be very different based on how the wind enters the stadium and where it goes before it leaves. Stadium jumps can be some of the most difficult demos around. Practice, practice, practice!
I hope that answered your questions.
Best Regards,
Bud Prenatt
Team Fastrax