Summary
We propose to adopt a new airworthiness directive (AD) for certain The Boeing Company Model 737-800, -900, and -900ER series airplanes. This proposed AD was prompted by reports indicating in- flight valve failure of the left temperature control valve and control cabin trim air modulating valve. This proposed AD would require replacing the left temperature control valve and control cabin trim air modulating valve. We are proposing this AD to address the unsafe condition on these products.