Date: 201207
Local time of day: 1201-1800
Location: ZDC.ARTCC, VA
Flight conditions: IMC
Weather elements / visibility: Thunderstorm; Turbulence
Light: Daylight
Aircraft: EMB ERJ 145 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Cruise
Airspace: Class A ZDC
ATC / advisory: Center ZDC
Aircraft component: Airspeed Indicator
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Confusion; Training / Qualification; Situational Awareness; Communication Breakdown; Human-Machine Interface
Second reporter function: Pilot Not Flying; First Officer
Anomaly: Aircraft Equipment Problem Critical; Deviation - Speed All Types; Flight Deck / Cabin / Aircraft Event Other / Unknown; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Aircraft Equipment Problem Dissipated; Flight Crew Became Reoriented; Flight Crew Requested ATC Assistance / Clarification; General Declared Emergency; General Maintenance Action
Contributing factors: Human Factors; Weather; Aircraft
Primary problem: Aircraft

Narrative: We were in cruise at FL360. We were contacted by Dispatch with a proposed reroute due to weather. We discussed the reroute; decided to accept it and altered course eastbound to avoid the weather. ATC altered the requested reroute and gave us a route would have taken us through heavy precipitation so we requested vectors further eastbound to avoid it. The initial plan was to pass through two areas of moderate precip then continue on course. While vectoring through the weather we realized the precip was building fast and would require us to pass closer by it than originally anticipated. In preparation we contacted Flight Attendant; and slowed the aircraft to .63 Mach. Light turbulence and rain were encountered and airspeed indications seemed to indicate the aircraft was slowly and steadily decelerating. I added power to increase speed. The aircraft did not seem to respond as well as usual for the low speed at altitude. The poor/slow increase in IAS prompted me to select CLB mode for more thrust. What initially seemed like just sluggishness for a given weight/speed/altitude started to look like a more serious problem. Possible windshear with decreasing performance crossed my mind. Airspeed continued to roll back or decrease and I instinctively pushed the thrust levers forward past the detents. Airspeed continued to slowly decrease so I instructed the First Officer to request lower so we could reduce our pitch angle and could get the situation sorted out. As airspeed continued to slow during the First Officer's radio call to request lower I felt it necessary for safety to drop the nose to avoid a stall. ATC denied the request for lower so I insisted the First Officer request lower once again but it was again denied by ATC for traffic. I had still not regained Airspeed and continued to lower the nose to about 500 FPM while indicating only 170 KTS. ATC asked if we were declaring an emergency I responded 'yes' to the First Officer and told her I would continue to descend and to get a turn to avoid traffic from ATC. I cannot recall what the ISIS [Integrated Standby Instrument System] was indicating at this point but just then the high speed warning sounded and I looked over to see the First Officer's indications were appropriate for the warning. I leveled off; assumed the #2 ADC was correct; coupled the aircraft to the First Officer's side and instructed her to be the flying pilot. As I began to cross check the instrumentation I wasn't sure which was correct. All three; the Captain's; First Officer's and standby systems read differently. We had no positive cross check. We wanted to rely on the ISIS but soon realized it was frozen at .78M with an incorrect altitude.Once we thought we had a handle on which instrumentation was correct we contacted ATC and notified them of an equipment malfunction and that we no longer met requirements for RVSM airspace. It seemed that the #2 side was correct but I cannot be sure of this; any of the 3 indications seemed to be wrong at some point. About 10 to 15 minutes later; around FL200; all three seemed to match up. 'SPS advanced' and amber 'ALT' and amber 'IAS' were present intermittently throughout the ordeal. At some points deviations were erratic and obviously false but the initial decrease to .63M and further were smooth and seemed trustworthy. Altitudes varied as well during the confusion so the actual deviation in altitude is just an estimate. At one point in time the ISIS seemed to be locked at redline .78M and the altitude steadily decreasing as both #1 and #2 altimeters indicated level flight. Maintenance was notified and the culprit was believed to be excessive water in the pitot systems causing erroneous readings. I was told by the Captain who was supposed to fly the next leg on the plane that Maintenance found no water in the system. The next the day we flew the same aircraft again and it seemed to operate normally.

Callback: The Captain said that; although they flew the same aircraft only a day later; he either hadn't noticed or couldn't remember what the logbook stated the maintenance response to the event had been. When asked about training for such anomalies and/or whether he was aware of an attitude and power setting combination that could be utilized to insure safe flight while troubleshooting air data related anomalies he responded that he had had neither such training nor was he aware of any power/attitude combination that would provide safe continued flight despite the loss of air data information. He was in the cockpit about to depart on a trip and stated he would be observing attitudes and power settings en route to develop a rule of thumb to inform himself as to a viable combination for his aircraft.

Second narrative: My airspeed indication was steady at 200 KTS and not increasing speed as the Captain added power.While this was going on I noticed my airspeed increasing; the airplane getting louder; amber IAS and ALT flag messages on my airspeed and altitude tapes. I was busy dealing with ATC at this time to see what was wrong but we were descending and I was comfortable because the airplane was louder again and my airspeed was up so I felt okay at the time. We finally start leveling off at FL340 and ATC asks if we can hold FL340; I cannot remember if I said yes or no to this question. Next thing I know is we get a 'ding; ding… high speed; high speed.' Captain looks at my PFD to see my airspeed indication saying red line. He was confused and quickly coupled the autopilot/flight director to my side. We calmed down for a second and I looked over at his side to see his airspeed indicating 170 KTS; while mine was indicating 268; almost a 100 KTS difference.I was flying at this time and the jumpseater in the jumpseat chimed in and said he thought the ISIS was right and we should rely on that. The Captain agreed and I did to at the time. They didn't notice me slowly increasing and decreasing the thrust levers on my own. As I did this I noticed the ISIS airspeed wasn't moving so I informed the Captain and told him I was going to pull the thrust levers back a little further to verify. I pulled the thrust levers back and my airspeed started to drop to about 230 KTS and then his was about around there; but the ISIS was still red lined and didn't move. We agreed to not trust the ISIS and that it was frozen. About a minute later the amber IAS/ALT flags went away and I noticed the ISIS's altitude now was starting to drop on its own and ended up being -500 FT off of my indication and the Captain's. Then a few minutes later the Captain's airspeed started to drop again and the IAS flag came back and he was now indicating 50 KTS slower than me. A few minutes later his airspeed matched mine again. ATC then started to descend us for approach. As we were descending we started to notice the ISIS unfreeze. Eventually all three airspeed and altitude indications matched. The Captain took the flight controls and flew the rest of the way uneventfully.


Synopsis: While deviating around weather and in moderate precipitation an EMB145 flight crew encountered widely divergent airspeed indications among the Captain's; First Officer's and Standby airspeed indicators. They initially were aware only that the Captain's speed was gradually decreasing and; only after receiving a mach overspeed warning; did they cross check and notice the First Officer's was touching the Barber Pole. They wrote up the event but failed to note the maintenance response when they flew the airplane the following day--when it operated normally.