That reunion you mention is the Vietnam Helicopter Pilots Association (VHPA) annual reunion held every July 4th Holiday at various locations in the country.
The VHPA is made up of helicopter pilots who flew in the Vietnam War...membership is open to pilots of all allied nations who flew there.
The web site for the VHPA is vhpa.org .
Normal attendance is about 2500 combat veteran pilots each year.
This year's reunion has several good activities planned to include a visit to the US Marine Barracks, the Smithsonian Aviation and Space Museum, and a wreath laying ceremony at the Vietnam Memorial.