Boeing 737 variant naming (Specifically in the case of Alaska Airlines) I've noticed something interesting about how Alaska Airlines' Boeing 737 variants are numbered. Generally, the aircraft type is a simple "100" number, i.e. 737-800. However, Alaska specifically seems to omit the last two zeroes in favor of "90," as in 737-990ER. Is there any reason for this? Does Alaska have something for it's 737s that other operators if the type don't?