B737 Wing anti-ice valve open NNC
Hi there,
the 737-800 QRH NNC Wing anti-ice valve open has a step in it that I struggle with a bit and I would appreciate some other opinions.
Here is the scenario:
During the climb wing anti ice is used. It is turned off as the aircraft climbs through about FL280 and exits cloud and the L VALVE OPEN light remains illuminated bright blue. In step one the checklist confirms for you that the valve is now failed open.
Step two sates " If TAT is above ten degrees C or there is no visible moisture; isolation valve switch to close, pack switch off, bleed air switch off.
In the scenario the TAT is about minus twenty and it is clear skies so by following the QRH you go down to one bleed.
Is the primary reason for doing this so that you avoid a bleed trip off due to having 9th stage air required, or is there another reason why it is detrimental to have one wing heated in clear air?
Your thoughts?