A few years ago a NetJets hit a glider at 17,000 feet. They glider pilot turned off the transponder (he had it on, as he was above FL180 earlier) to save battery power. Everyone lived (the glider guy had a chute on and bailed out). Both airframes were destroyed.

https://www.google.com.hk/imgres?img...AEwAQ..i&w=240

https://www.google.com.hk/imgres?img...act=mrc&uact=8