They were required to by an airworthiness directive. https://www.federalregister.gov/documents/2017/06/29/2017-13409/airworthiness-directives-airbus-airplanes

They were required to by an airworthiness directive. https://www.federalregister.gov/documents/2017/06/29/2017-13409/airworthiness-directives-airbus-airplanes https://www.federalregister.gov/documents/2017/06/29/2017-13...