Date: 201704
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: IMC
Weather elements / visibility: Turbulence; Thunderstorm
Light: Daylight
Aircraft: EMB ERJ 145 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Air Data Computer
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Confusion; Distraction; Time Pressure; Troubleshooting
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Critical; Deviation - Speed All Types; Inflight Event / Encounter Weather / Turbulence
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Aircraft Equipment Problem Dissipated; Flight Crew Diverted; Flight Crew Landed As Precaution
Contributing factors: Human Factors; Weather; Aircraft
Primary problem: Aircraft

Narrative: When we leveled off at FL370 and noticed an amber IAS indication. When we checked the airspeed indicators we noticed that the FO's airspeed was indicating lower than mine and the standby airspeed indicator. As we accelerated there was no change in his airspeed indicator. Based on this I thought there was a blockage of pitot tube 2. The PM pulled out the QRH and it instructed us to do an ADC (Air Data Computer) reversion. This also required us to descend out of RVSM airspace. ATC assigned us FL270 and we began to descend. We descended with the autopilot on. As we descended we noticed the standby IAS and Captain side no longer matched up. Captain side IAS was descending and acting like an altimeter. This caused some uncertainty initially as we were not sure which one to believe. We were asked to increase our descent by ATC so I increased the VS to 2000 fpm. Shortly after this the airplane did an uncommanded pitch down and we disconnected the autopilot. It was at this point smoke or water vapor came pouring in through the window seals. I wasn't sure which it was at first; but it made me worried about our pressurization and we were still at FL300 and hand flying. I checked the cabin pressure on the EICAS and it seemed normal. About at this point we also experienced a failure of both ADCs as we got red Xs across our instruments. I also saw an IC-600 failure message on the EICAS and the first officer reported seeing a PRESN auto fail message. We [advised ATC] and proceeded to ZZZ. We received radar vectors there. As we descended the systems came back online and by the time we were getting vectors to ILS all indications were normal again. At some point I turned the autopilot back on but it kicked off after we intercepted the localizer as the localizer was swaying back and forth. After that we landed uneventfully at ZZZ.Bad weather; instrument failure; task saturation. The autopilot pitch down was caused by me leaving the autopilot on after I should have disconnected it. At the time I was busy and it did not occur to me that I should turn the autopilot off. At that time I was busy trying to decide which airspeed indication I could rely on and trying to figure out what was going on.


Second narrative: The flight started about 1.5 hours delayed due to a line of severe weather. Our filed route took us north with expected vectors around the west side of the most severe elements of the line. Previous aircraft had flown through our route without any issues. We reached our cruising altitude of 37;000 ft. and were leveled off for approximately 9 minutes before we received an amber IAS indication on the PFDs. Taking note of the three airspeeds revealed the FO side was in disagreement with the standby and captain's side PFD. I pulled the QRH. The guidance provided stated to compare data with the standby indicator and if required use cross-side data by pressing the appropriate reversionary button. We did this resulting in the FO side airspeed reading in agreement with the captain's side and standby instruments. Further guidance also instructed us to descend below RVSM so I as the PM called ATC and requested a non RVSM altitude for a minor issue with our airspeed indications. At that point the problem seemed solved and we intended to continue as planned. It was during the descent; however; that the real alarming airspeed indications began to manifest. As we got lower; all three airspeed indications fell out of agreement and all trended lower with each bit of altitude lost. Obviously we were both extremely alarmed at this indication and I began thinking out loud about what would cause the result. My thought was that a partial pitot tube blockage which prevent air from entering the tube but not preventing it from escaping would possibly result in this reading. This thinking was based on static pressure continually increasing as we descended but ram air pressure remaining unchanged. This would result in an ever increasing static to ram air pressure ratio thus resulting in a lower airspeed indication. My mind immediately went to [a recent aircraft accident] which crashed due to pitot tube blockage and an improper pitch and power setting in response to inaccurate airspeed indications. The time spent during the descent while the airspeed was rolling back was incredibly stressful as it was IMC in the thin air of 35;000+ feet. I am certain both of our minds were trying to figure out as rapidly as possible what was happening in order to best figure out how to handle the problem. Any EICAS indications which may or may not have existed during that period went unnoticed as the evaluation of whether or not a stall at 30 something thousand feet was imminent took precedence over all other things. Once I was done verbalizing my theory on the pitot tube blockage and we both agreed it was a real possibility; our focus became pitch and power and working together to ensure the aircraft continued to fly safely in the descent. Up until this point the captain had elected to continue to let the autopilot fly; perhaps due to the thin air; but we were both very aware of the probable need to disconnect it when our airspeed indication read very low. I don't think either of us knew for sure what the Autopilot was going to do at such low airspeeds which in hindsight should have been a trigger for the captain to hand fly the aircraft but there was a lot to think about at that point. When the airspeed indication (not actual airspeed) read dangerously low the autopilot commanded a very rapid pitch down attitude. The captain immediately disconnected the autopilot and I jumped on the controls with him to pull the nose back up to a safe descent attitude while also trimming the nose up to relieve the pressure. I notified ATC of our situation. I asked if there was any known VMC in the area but none could be found. ATC offered ZZZ as the closest suitable airport and provided vectors to the field. At some point during our continued descent we lost all airspeed and altitude indications as both PFD's were covered in red Xs. A number of EICAS indications were presented which again took a back seat to flying the aircraft; getting setup to land at an airport now less than 30 miles away with a Metar of TSRA over ZZZ. Honestly there was so much going on as the PM that the only EICAS message that was clearly noted in my head was PRESN auto FAIL. Perhaps this was because it seemed like a completely new problem in the storm of events. It was somewhere around this time; likely before I noticed PRESN auto FAIL; that our windows were completely fogged over and both the Captain and FO side windows were venting in visible water vapor. The windows were so obstructed that I initially thought we had severe clear ice buildup on our windows further adding to my workload as it produced even more stress to an already very stressful event. Concerns of seeing a runway with an obstructed windscreens became the next thought in my head so I moved on to trying to solve that problem. There were no indications of failed windshield heat; however; I checked the windshield heat buttons at least three times to make sure they were on and even cycled the captain's side as I have never seen so much condensation on a heated windscreen before. I eventually had a moment to grab the box of tissues we thankfully had on the fight deck and was relieved to find our visibility issues were solved after wiping down the front windscreens. While we didn't get into VMC conditions until around 2;000 feet on the approach; we did at some point during our descent into ZZZ get all of our indications back and in agreement with no reversions. To the best of my knowledge we were within 10 miles of the field and getting vectors for the ILS when our instrumentation resumed what at least appeared to be a normal operating condition. I would be dishonest if I said I wasn't very skeptical of all instrument indications at that point after all we had been through thus far. Because the indications were in agreement the Captain elected to reengage the autopilot again for our arrival into ZZZ. Keep in mind from the point of failure when the Captain took the controls from the autopilot until right now in the scenario; all that I have been doing from the right seat has been in conjunction with being equally focused on watching the captain's flying to back him up on his pitch and power. Nothing was more important in my mind than 1. Preventing a stall and 2. Ensuring we didn't descend the aircraft into the ground due to task saturation. Our descent into ZZZ was constant moderate precipitation and despite an ATIS indicating TSRA; Approach had two aircraft which had recently landed; thus encouraging us to continue into ZZZ. In one last reminder from the aircraft to never stop flying until you are safely on the ground; the autopilot started badly s-turning on the localizer and the autopilot disengaged itself. The captain of course took the controls again and hand flew the ILS to the runway to land without any further issues. Some of the major threats included severe weather along the route of flight as well as a malfunctioning aircraft with incorrect indications provided by the instrumentation. The most significant factor was the uncommanded pitch down by the autopilot due to not hand flying sooner. That would stand out to me as our biggest error. We both were unsure of what was going to happen with the autopilot in charge so allowing the autopilot to take it for as long as we did was not necessarily wise. It did; however; free up both of our brains a bit more to decide what was happening and how to respond. The only positive I can take from this was we were at least watching the airplane like a hawk ready to take corrective action immediately if a proper pitch attitude wasn't maintained. As soon as it was apparent the autopilot wasn't up to the task; we took over. We experienced a very nasty mix of major task saturation which couldn't be aided by an autopilot as well as honest to goodness fear. Stalling the airplane in IMC was hard to not think about; nor did I wish to try. Aviate-Navigate-Communicate was definitely our approach. It doesn't do any good to flip through a QRH while death spiraling toward the ground after a stall. That being said; at no time did I ever make a decision to not follow the QRH. I simply did not have enough free resources to get there before the messages eventually cleared and the PFD's appeared normal again. With so much going on; including the water vapor and suspected icing; working with ATC to get us to ZZZ; having to consider the weather and the TSRA in the ATIS; getting numbers for the runway; setting up frequencies; briefing approaches and running the arrival check and sending a diversion report to dispatch; I simply never had the time. Had this been a sim where the consideration of myself and other peoples lives were not on the line; I probably would have been better able to address the EICAS messages which may or may not have corrected our instrument indications. Unfortunately; this was the real world and we both did the best we could with everything which was thrown at us. While I feel overall we did ok with the situation presented to us; there are always things you could do better. Certainly as previously mentioned; the autopilot should have been disconnected sooner in order to prevent the need to take sudden corrective action. I do wish I had been able to get to the QRH after the initial ADC (Air Data Computer) reversion. I really tried my best to clear my mind and focus on the tasks required. Unfortunately; I couldn't stop hyper focusing on the aircraft state and trusting the Captain to fly correctly. It wasn't because I didn't generally trust his skills; it was simply a scenario which is very rare (never happened in my experience) and had a severe enough outcome (high altitude stall) if improperly executed that I felt backing him up took priority. Especially since with all that had gone wrong; my trust of any indication outside of the standby indicator (even my trust here wasn't very strong) was gone; despite what they were or were not reading.


Synopsis: EMB145 flight crew reported an airspeed indication failure at FL370 in IMC with thunderstorms nearby. The flight diverted to the nearest suitable airport with airspeed returning to normal during the approach.