CRJ900 pilot crew reported the #1 air data computer malfunctioned causing numerous instrument failures and an altitude deviation.
Synopsis
CRJ900 pilot crew reported the #1 air data computer malfunctioned causing numerous instrument failures and an altitude deviation.
Narrative
At Cruise at FL360; we were experiencing a fairly lousy ride. Vertical speed was indicating -/+200-800 FPM consistently and at one point showed +2700FPM (now believed to be erroneous due to failures listed below; and that we did not feel any extreme variations in the plane). We asked for different altitudes; trying FL340 and FL320; looking for a more comfortable ride. We were over eastern ZZZ (somewhere around ZZZZZ fix); and the Controller we got handed off to told us 1/2 our radio transmissions were not coming through. We tried a second comm; with no real improvement on their end; we could hear just fine. None of the previous 6 Controllers had mentioned this to us. We got an EFIS COMP MON caution message and its associated altitude (ALT) flag on the First Officers (FO's) Primary Flight Display (PFD). It disappeared a few seconds later by itself. This process repeated several times in the next few minutes; and then both Captain and FO were getting ALT flags and EFIS COMP MON caution. We ran the QRH for EFIS COMP MON ALT; and based on the FO's side throwing more flags; as directed in the QRH we initially selected to AIR DATA 1. The airplane's autopilot sent us up 700 ft. to FL32700 before we took control and corrected it to FL320. We told ATC that we were running a procedure and were in the process of returning to FL320 and it was not an emergency. ATC acknowledged that with no further comment. Based on this behavior; we now knew Air Data 1 was the system that had failed; and selected Air Data 2; per the QRH. This resolved the EFIS COMP MON and ALT flag. We did not believe that unreliable airspeed was a concern; and followed up with the second indicated QRH (air data computer failure) and sent messages to Maintenance and our Dispatcher. The air data failure QRH told us to expect L R FADEC FAULT; RUDDER LIMIT FAULT and SPOILER STAB TRIM FAULT status messages. SPOILER STAB TRIM never displayed. We were busy getting weather; landing numbers and getting all other tasks accomplished. On approach; the autopilot kicked off twice with no apparent malfunctions. Fun day. Air Data computer died. Its an unusual failure and thankfully not a common issue.This one is so unusual that even our great mechanics thought it was uncommon. General training on properly running QRHs and delegating flight deck responsibilities in flight used existing skills to deal with an uncommon issue.
Second reporter narrative
While in cruise from ZZZ to ZZZ1 the flight crew encountered an EFIS COMP MON message due to altitude difference in the Captain and First Officer altimeters. The QRH procedure was ran and during the procedure the crew was instructed to select the operating ADC source. When the suspected correct source was selected the aircraft pitched to correct the altitude deviation of approximately 800ft. The altitude was corrected and reported to ATC. Additionally; both the First Officer (FO) and Captain altimeters both gave altitude flags in addition to vertical speed indicator fluctuations of +- 1500fpm. The discrepancy was reported to Maintenance.Issue was caused by disagreement of altitude from inaccurate air data computers.
More incidents for this aircraft family →
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.