Date: 201901
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Dusk
Aircraft: Regional Jet 200 ER/LR (CRJ200)
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Initial Approach
Airspace: Class B ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Altimeter
Component problem: Improperly Operated
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human factors: Situational Awareness
Second reporter function: Pilot Flying; First Officer
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Altitude Excursion From Assigned Altitude; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Returned To Clearance; Flight Crew Became Reoriented
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: I was the pilot monitoring. We were leveling at four thousand feet and about 12-15 miles out on the ILS XXR. I was in green needles. ATC assigned a speed reduction of 210 to 170 knots and had cleared us for the visual approach. The pilot flying had the autopilot engaged. The aircraft suddenly began a descent and increased speed. I called for the pilot flying to stop descent. I felt automation was incorrect and stated 'my aircraft' and disconnected the autopilot and corrected for 300-400 foot altitude loss. At this point I transferred controls back to the original pilot flying and re-engaged the autopilot. Moments later the aircraft started a descent. Again I called 'my aircraft' disconnected autopilot and corrected back onto the glideslope and speed correction to 170 knots. ATC had advised us for a 2nd or 3rd time they needed speed of 170. We were at 170 knots at his last request; but speed management was not my first priority when detecting and correcting for the unexpected descent. After stabilizing the aircraft I noted the original pilot flying side altimeter read 31.22 and it was determined that the original pilot flying was turning the baro knob instead of the NAV select knob when transferring to green needles. In doing so; the aircraft thought we were higher and needed to descend to 4000 feet. There were no traffic conflicts and we were cleared on a visual approach.The pilot flying had the correct altimeter settings prior to the approach. The baro knob was inadvertently turned instead of the nav select knob. The location and size of the knobs are similar with the baro knob located just below. The only indication we had which was at the initiation of descent was an altitude chord sound which still took a moment to detect and react to the aircraft descending. Perhaps a message anytime there is a discrepancy between the altimeter settings set on the PFDs to caution the pilots.


Second narrative: We were on a visual approach to XXR at ZZZ. When changing the nav source from FMS to loc; I inadvertently spun the baro knob instead of the nav source knob. This caused the expected problems and confusion sorting things out. I was slow to reduce airspeed from 200 to 170; and ATC asked two additional times for us to slow. No conflict occurred. The plane also descended prematurely but we were on a visual approach so no deviation should be recorded. This was an unusual deviation that had never occurred before for me. But I am aware of the possibility that this could happen to anyone. Of course; we must look at what we are moving and verify the input causes the desired results afterwards. But it would be wise to change the baro knob to one that has a different tactile feel than the nav knob. The knobs are identical and close to each other on the side panel. Also; why is there no caution and chime when the altimeters differ by a drastic amount; as they did in this case? The electronic capabilities of this plane certainly can accommodate detecting a difference in altimeter values; but no caution and chime are produced. I cannot imagine why they didn't think of this. This airplane produces a myriad of cautions and chimes when shutting down the engines at the gate; with the parking brake set; all of which are ignored. All the cautions and chimes are related to the normal condition expected upon engine shutdown. If an actual abnormal malfunction happened at that time; it would not be detected due to all the other chimes and cautions. I suggest finding a way to permanently mute all chimes associated with normal cautions during a normal engine shutdown; (parking brake set; etc). That way; if an abnormal malfunction occurs; the chime will not be ignored. It will be noticed because that chime will be the only one produced and heard. The crew will then look at the cautions displayed and see that the top one on the list needs attention. Here we have an airplane that has no alert when the altimeters differ in flight (a pretty important thing); and excessive aural alerts when the engines are shut down at the gate (all of which are ignored.)


Synopsis: CRJ-200 flight crew reported an altitude excursion occurred when the altimeter baro knob was spun instead of the nav source knob.