<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by FWAAA:
It's a big plane, fairly new, with two very powerful engines and two very large wings. 
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It also has some fairly large overhead bins, compared to other aircraft in the fleet. I recall when UA put them into service they mentioned there were separate climate controls for each cabin, something that was lacking in other Boeing models at the time.