Date: 201504
Local time of day: 0601-1200
Location: DCA.Airport, DC
Flight conditions: VMC
Weather elements / visibility: Thunderstorm; Turbulence
Light: Daylight
Aircraft: EMB ERJ 145 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class E ZDC
ATC / advisory: Center ZDC
Aircraft component: Altimeter
Component problem: Improperly Operated
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Human factors: Situational Awareness; Confusion
Second reporter function: Pilot Flying; Captain
Anomaly: ATC Issue All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Contributing factors: Procedure; Human Factors; ATC Equipment / Nav Facility / Buildings; Weather
Primary problem: Ambiguous

Narrative: Prior to the start of the arrival we had been deviating around thunderstorms and I had put the ATIS on auto update since there were thunderstorms in DCA.  Around FL240 we had been told to expect the south transition. However; ATC changed us to the north transition and then back again to the south transition based on changing winds at the airport. At FL210; they cleared us for the FRDMM arrival. During this time they then cleared us via the TRUPS. I inquired and that was given in error and we were recleared to descend via the FRDMM arrival. I also inquired on landing runway since the ATIS was giving a different runway than he assigned. He said that the ATIS was giving out the wrong runway ONLY.    I started to notice that the ATIS updates were changing at a rapid pace; consistent with a thunderstorm passing over the field. The first ATIS included a squall line passing. We initially received an ATIS and by the time the events ended we were back [near beginning of the alphabet.] I do not remember being given an altimeter setting from ATC and when we performed the inrange [checklist] I gave the most up-to-date altimeter setting which was 29.54 to the Captain (CA).   As we were approaching PLDGE; the controller told us to immediately stop our descent and to hold at PLDGE. We were less than 5 miles from PLDGE and quickly rushed to put the hold in the FMS. He said expect 1 turn in the hold and to level at 17;000. Also; we were instructed to slow as well. He said all of this was due to flow into DCA. We had started to hold when the controller asked us what altitude we were at. I said 17;000 and he confirmed that this was not what he was showing. I said we were level at 17;000 and current altimeter 29.54. He quickly stated that this was wrong and current altimeter was 30.04. He said he informed us earlier that the ATIS was wrong. The CA and I both agreed that earlier he had told all aircraft on frequency that the runways were wrong and that was it. There was no mention about altimeter. The controller told us we were not listening. Numerous other aircraft were inquiring about runway and altimeter settings.     After one turn we were recleared direct to PLDGE and given a descent to 16;000. As we started to descend he told us again to descend to 16;000 and once there recleared the FRDMM arrival. We had unfortunately took that as a 'descend via' and not a 'cleared via' The controller inquired about our altitude being off and informed us of our error of descend vs cleared. From there the rest of the arrival was uneventful and we asked for correct altimeter settings with each frequency change. Initial threats were the arrival itself and thunderstorms in the area. During the arrival we were given unexpected close holding; speed reduction; and descents that were not on the arrival. ATC also gave us the wrong arrival and switched landing runways 3 times. ATC only informed us that the ATIS included the wrong runway and DID NOT mention that the altimeter settings being produced were wrong. The errors were the two altitude deviations. The second coming from a high stress and workload environment created from the first one. I believe the quick hold; descent; and speed reduction; followed by the constant weather updates and deviating with storms caused us to confuse the descend via and the cleared via clearance at the end of the event. I believe we should have told ATC we were unable for the hold. We were too close to the fix and combined with our altitude and speed reduction our workload was already too high. Especially after dealing with the wrong altimeter setting and confusion. I also think there needs to be clarification if the ATIS is wrong. When we landed in DCA and asked ground if the departure ATIS was correct he informed us that it was a national outage and that they were producing wrong information. I think this was an urgent issue and should have been communicated better with working crews; possibly via a messagefrom dispatch or ATC. When I first inquired about the runway change on arrival; the controller had no idea that it had been changing to begin with. He informed us only that the runway on the ATIS was wrong and nothing else.


Second narrative: [Report narrative contained no additional information.]


Synopsis: An EMB145 flight crew experienced the digital ATIS altimeter setting anomaly experienced by so many other flight crews on this day. Two altitude deviations occurred. The first due to the altimeter setting and the second when the crew started to descend via when only cleared via the FRDMM3 arrival. Thunderstorms and holding patterns compounded the situation.