UPDATE 2-American Airlines flight attendants stand up to Boeing CEO on 737 MAX

American Airlines' flight attendants union still has safety concerns about the Boeing 737 MAX and is demanding an active role in the relaunch of the grounded aircraft, its president told Boeing Co's chief executive in a letter seen by Reuters. "The 28,000 flight attendants working for American Airlines refuse to walk onto a plane that may not be safe and are calling for the highest possible safety standards to avoid another tragedy," Association of Professional Flight Attendants President Lori Bassani said in the letter.