Hi all! My first post on the forum! Anyway, I was at gravelly point park just north of runway 19 at KDCA last night. At 7:40-7:45 the emergency vehicles all rushed out and positioned themselves on various taxiways near runway 19. Not long after, two police boats came down the potomac river and parked in the water as close to the airfield as possible. Around 7:50 pm a republic airlines (us airways express) e-170 landed on runway 1 and it appeared to be a completely normal landing. It taxied to the end of the runway, turned left on taxiway J, and parked on the holding pad off of taxiway J. The emergency vehicles then all circled the aircraft and some responders got out and walked around the aircraft looking at the underside and wings. This went on for about 10 minutes until the trucks pulled away and the aircraft taxied to the C gates under its own power. I listened to liveatc and found that it was republic airlines flight 3392 from KMSP-KDCA. The only bits I could discern were that when tower cleared YX 3392 to land, the controller said something to the tune of "we'll have the trucks waiting when you arrive". However, that's as far as I could get in my search to find out the cause of the emergency, and was wondering if anyone on here had any further information. The thing I found interesting was that police boats were called in from the potomac, which at first had me thinking a threat to security. However I dismissed that as no one was ever taken off the aircraft, the police never left their vehicles, and the fire crews were inspecting the airframe themselves. Any help or further information on what happened would much appreciated!