Originally Posted by
Wide Mouth Frog
I'm not sure they did say that about the altimeter, they said that there was bad pressure altitude data recorded on the FDR. That's not the same as saying the altimeter display was wrong, although it does mean that it's going to be hard to infer what was actually displayed on the Baro Alts. I would have thought a military crew would be pretty solid on altimeter cross checks though so I think that's all a bit of a red herring. The Potomac is (give or take the tide) at sea level so I think we can be pretty confident that the RadAlt figure of 278ft is good for an altitude too.
When I checked the field elevation at National/Reagan/DCA, I see 14'.