DC started going super senior back in mid 90s when the RDU base closed - there was a mass migration of RDU folks up there. It stayed very senior until mid last year when we started seeing movement and upgrades. Right now recalled folks, as OFD said, are getting awarded DC after only a month or so on the line.

Having been based in DC my first two years, I will say this. Small base, everyone knows each other. VERY small IAD operation, pretty much limited to flights to DFW on the MD80, MIA on the 737, SJU on the 757, and a couple of transcons to LAX on the 737/757. Most of the flying is out of DCA (MD80, 737) and BWI (MD80, 757.)

Hope this helps.
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