By Mike Dougherty

PHILADELPHIA (CBS) — “This is an incalculable tragedy,” says Philadelphia AIDS activist Jane Shull, executive director of “Philadelphia Fight.”

READ MORE: Upper Darby High School Dismissed Early After Student Sets Paper Towel Roll On Fire In Bathroom

She and many others are heartbroken at the news that about 100 AIDS doctors and activists were aboard Malaysian Airlines flight 17, which was shot down over the Russia-Ukraine border yesterday (see related story).

Among them was Dr. Joep Lange (top photo), a Dutch doctor who was the former president of the International AIDS Society.

READ MORE: Lockdown Lifted At Hardy Williams Mastery Charter School After 911 Call Warning Of School Shooting

Dr. Pablo Tabas, an AIDS researcher at the University of Pennsylvania, says Dr. Lange will be missed by many.

“He was always very outspoken and he said what he thought, and that sometimes put him into trouble, but it was good trouble in the sense that he generated discussion and generated interest,” Tabas said today.

He says Dr. Lange was a pioneer in the AIDS research community who didn’t always follow the crowd, and that he should be remembered as a man who was always an advocate for patients — someone who put people first.

MORE NEWS: Bipartisan Congressional Talks On Overhauling Police Practices End Without Agreement, Sen. Cory Booker Says