(CNN) Flight attendants are mourning the death of a beloved colleague this week as they keep working in conditions that they say feel increasingly dangerous.

Paul Frishkorn, a longtime union representative and Philadelphia-based flight attendant for American Airlines, died this week, the airline confirmed Wednesday in a statement to CNN.

Authorities in Pennsylvania have yet to release a cause of death. But in the voicemail greeting on his phone, Frishkorn said he was "very ill" and awaiting results of a test for Covid-19

"He was amazing, and totally selfless, and just a ... good soldier who never asked for any recognition, other than to make sure people were taken care of," Sara Nelson, president of the Association of Flight Attendants, told CNN in a phone interview, her voice breaking with emotion.

Frishkorn was in his 60s. He had twice been named one of American's Flight Service Champions for excellent customer service. "Our hearts go out to Paul's family and friends, many of whom work for American," the airline said. "We are working directly with Paul's family to ensure they are cared for during this extraordinarily difficult time."

Read More