Flight Crew Air Transport Pilot (ATP)
Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural FAR
Flight Crew Returned To Clearance
Human Factors
On the descent on the arrival; we received a clearance to descend and maintain FL180 near. The altitude was selected and confirmed and a descent was initiated. This clearance is uncommon on this arrival and we were anticipating to continue the descent for the expected ZZZZZ Intersection crossing at 8;000. Passing through roughly FL185 we began to adjust the altimeters for the transition forgetting that we were leveling off at FL180. We began the altimeter transition slightly early due to an abnormally high altimeter setting (30.43) and the effects that it has on a VNAV descent path especially with a strong tailwind. As we began leveling off we remembered that we were cleared to level off at FL180 and therefore had the wrong altimeter setting in. We immediately readjusted the altimeter to STD (29.92) which then showed us roughly 400 feet low. We immediately climbed back up to FL180 with the appropriate altimeter setting. No conflict was noted and ATC did not seem to notice. We deviated from our clearance altitude for a total of roughly 20 seconds. This was definitely an example of expectation bias and a breakdown of established procedures. As the Pilot Monitoring (PM); I failed the Pilot Flying (PF) when I did not adhere to sterile cockpit procedures within 1;000 of level off. We had received a confusing radio transmission from Center shortly before the event and it distracted us and caused me to lose situational awareness momentarily. I was also looking at the STAR on the iPad instead of monitoring the level off as I should have. Adhere to established procedures.
Cleared to descend to FL180 while on Arrival. There is a crossing restriction of 8;000 at ZZZZZ Intersection. With an abnormally high altimeter setting I tried to slowly adjust the altimeter so as to make a smooth transition thru FL180 to avoid a pitch over on the vertical path with the strong tailwind. I had forgotten we were told to maintain FL180. We are usually given the crossing at ZZZZZ Intersection prior to this point and would continue descent. After we leveled (at 18;000) I immediately realized my error. When resetting STD on altimeter we were actually at 17;600. I corrected back to FL180. No conflict occurred and ATC seemed not to notice. Flight continued normally. I had an expectation bias and thought I was being proactive for a smoother flight. Lesson learned. Simply trying to make a smoother consistent descent path. Greater situational awareness that we were cleared to maintain 180 and not planning too far ahead for continuing descent as I had expected.
EMB-190 flight crew reported inadvertently setting local altimeter while assigned FL180.