Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Situational Awareness; Time Pressure
Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented
Human Factors
While on arrival into ZZZ the aircraft was descending to 3000 on a 360 heading base leg to Runway XX. Just prior to capturing altitude; ATC issued a heading to intercept the localizer; maintain 3000 until established and cleared us for the ILS 28. The Captain; as PF; reached up and spun what they believed to be the heading bug and was reaching for the approach button. I realized as we descended through 2800 that the knob spun was the altitude alerter set knob. I took the controls momentarily; used TCS to override the autopilot as we reset 3000. We descended to 2700 as this was happening and climbed back up. About this time; ZZZ Approach saw that we were low; and advised us to maintain 3000. I replied that we were returning to the assigned altitude. We leveled at 3000; armed the approach and completed the ILS to landing. I believe the threat occurred due to the 'muscle memory' of the Capt. We were in a familiar location as they had been flying out of ZZZ for their entire career with the last bunch of years being on the CRJ. As we were cleared to turn and intercept the localizer; the Capt's hand went to where the heading bug has 'always' been. In the new aircraft; this is approximately the location of the altitude selector knob. By spinning the knob left for a turn; they selected a lower altitude prior to the aircraft capturing the previous selection. While I was busy talking with ATC; I do not believe that I was task saturated but it did take a moment for me to recognize what had been changed and be able to override and fix it. After landing; the Capt and I thoroughly discussed what happened and steps that could be taken to preclude this type of event from happening with the first thing being that with the new aircraft; everything needs to be done at a deliberate pace. Look before acting. As an LCP [Line Check Pilot]; I am very aware that pilot's fall into habits and routines. In most instances; this is a good thing as this helps free up cognitive abilities so we can concentrate on larger tasks. I do brief pilots; especially now that we are transitioning to a new; unfamiliar aircraft that we need to be methodical and deliberate when we are making changes. Look at where your hand is before making a selection. This will help when we are in that 'same old; normal position' in space and time when our old habits kick in and can cause errors.
EMB-175LL Check Airman reported altitude deviation due to PF selecting altitude knob in what was heading knob on older aircraft.