AD FAA-2019-0478

The FAA is superseding Airworthiness Directive (AD) 2017-12- 07, which applied to certain The Boeing Company Model 737-800, -900, and -900ER series airplanes. AD 2017-12-07 required replacing the affected left temperature control valve and control cabin trim air modulating valve. This AD retains the requirements of AD 2017-12-07, expands the applicability to include additional airplanes, and adds a new requirement for certain airplanes to identify and replace the affected parts. This AD was prompted by reports of in-flight failure of the left temperature control valve and control cabin trim air modulating valve. The FAA is issuing this AD to address the unsafe condition on these products.