Originally Posted by
IslanderDriver
Rarely flying domestically I found the now "old" procedure of setting QNH when cleared below TL more confusing than helpful, especially on arrivals with descend via clearances. Added another layer of mental gymnastics when it's really just simpler to wait for the FL180 and call for the checklist. It's why most airlines have a inrange checklist at FL180.
Asked some of my friends at other airlines. Some actually do In Range or Descent checklists before top of descent...before it starts getting busy.
I think it makes most sense to change the domestic altimeter at 180. That’s what we’ve done forever, and it coincides with our In Range checklist. International is different because nearly every country has a different transition altitude, many of them very low. But, even over there, it is sometimes confusing to select QNH far before you cross the TL, especially when there often is a call to level off prior to the TL by ATC due to traffic (I’m thinking Korea, China). The international industry standard should be to select it as you cross the TL. It makes it certain that you are at the proper altitude when you should be, despite vectoring and early level offs by ATC, and acts as a reminder to international crews of exactly where that TL is. My two cents. (Due to Obama’s Treasury Dept. printing money, it’s now more like a half-penny’s worth).