Let’s get this out of the way: Alaska Airlines is NOT All-Boeing. The airline operates 75 Embraers, which it means to keep for many years. The following chart shows the steady Boeing growth at the airline. Embraer
has a lock on about a quarter of the fleet.
Alaska Airlines Fleet
The following chart shows the steady move to Boeing. Simplifying the fleet is universally thought to lead to better operational costs. The Air Current has an excellent interview with the airline’s fleet head, discussing the logic of standardizing on the 737. Moreover, the MAX9 is the greenest aircraft in US service.