The other fatal mid air with tow plane happened in Crazy Creek 10 years ago, not Williams.
Mid air with tow planes are rare but happen and usually tragic with multiple fatalities.
There was another bad fatal mid air between a glider and power plane in Canada few years ago.
Overall, mid airs are not so rare and the combination of powerflarm and ADS-B significantly reduces the overall risk. I fly with both and wouldn’t want to fly in a glider without it. I am shaking my head in disbelief whenever I see a glider without powerflarm in the Great Basin risking all of us who use powerflarm.
My comments are not specific for this accident. I have no details about this accident and if powerflarm/ADS-B would have made a difference, especially if they collided due to getting out of position.
My condolences to all impacted, which is the whole gliding community to some extent. It is especially tragic when a passenger/student get killed (18 years old this time!), and this happen too often in the last couple of years..

Ramy