Narrative:

On descent the altimeter was abnormally high (30.51) which was briefed. As we passed through FL180 on our way down to our assigned altitude of 13;000 feet the altimeters were set; the descent check flow was accomplished; and a series of radio calls were made. I was pilot monitoring and became focused on these tasks which I allowed to distract me from running the descent check promptly. The first officer (first officer) made the 1000 feet to go call; as we passed through 14;000 feet approaching 13;000 feet. I quickly glanced at my altimeter setting and called out 14;000 feet descending 13;000 feet. My altimeter and the standby altimeter were set to 30.51; but the first officer's altimeter was incorrectly set to 31.51...exactly 1 inch higher than reported; causing us to be ~1000 feet lower than intended. When he made his call; my quick glance at my altimeter failed to catch that we were actually at 13;000 feet descending to 12;000 feet. I had expected to see 14;000 feet and that expectation kept me from seeing our actual altitude of 13;000 feet on our way to 12;000 feet. During this time we had received a hand off to approach control and I had waited until altitude capture (altitudes cap) before reporting in. After seeing the altitudes cap I made the radio call that we were leveling at 13;000. As I said this and referenced my altimeter; I immediately saw the discrepancy and then cross checked the first officer's altimeter; discovering the error...but too late. The controller gave us a descent to 6000 feet and asked us to verify our altitude. We continued our descent and the first officer's altimeter setting was corrected and then the descent check was finally accomplished. The descent; and subsequent visual approach were uneventful.my delay in running the descent check promptly as we were descending through FL180 contributed to the altitude deviation. Also; my expectation of what I should be seeing on the altimeter vs. What was actually being displayed during the 1000-to-go call also contributed to this simple mistake not being caught. The fact that the altimeter was set exactly 1 inch too high; thus causing the altitude to be off by almost exactly 1000 feet was a horrible coincidence that fed into my expectation. Another possible factor was the unusually high altimeter setting that is not typically seen may have contributed to the first officer's input error. Promptly running the descent check through FL180; and certainly before any intermediate level offs; I believe; would have brought the error to light sooner. Being less complacent during the critical 1000-to-go call would also have been crucial in not allowing my expectation to cloud reality.

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Original NASA ASRS Text

Title: CRJ-200 Captain reported descending below cleared altitude when the altimeter was accidentally set incorrectly.

Narrative: On descent the altimeter was abnormally high (30.51) which was briefed. As we passed through FL180 on our way down to our assigned altitude of 13;000 feet the altimeters were set; the descent check flow was accomplished; and a series of radio calls were made. I was pilot monitoring and became focused on these tasks which I allowed to distract me from running the descent check promptly. The First Officer (FO) made the 1000 feet to go call; as we passed through 14;000 feet approaching 13;000 feet. I quickly glanced at my altimeter setting and called out 14;000 feet descending 13;000 feet. My altimeter and the standby altimeter were set to 30.51; but the FO's altimeter was incorrectly set to 31.51...exactly 1 inch higher than reported; causing us to be ~1000 feet lower than intended. When he made his call; my quick glance at my altimeter failed to catch that we were actually at 13;000 feet descending to 12;000 feet. I had expected to see 14;000 feet and that expectation kept me from seeing our actual altitude of 13;000 feet on our way to 12;000 feet. During this time we had received a hand off to Approach Control and I had waited until Altitude Capture (ALTS CAP) before reporting in. After seeing the ALTS CAP I made the radio call that we were leveling at 13;000. As I said this and referenced my altimeter; I immediately saw the discrepancy and then cross checked the FO's altimeter; discovering the error...but too late. The controller gave us a descent to 6000 feet and asked us to verify our altitude. We continued our descent and the FO's altimeter setting was corrected and then the descent check was finally accomplished. The descent; and subsequent visual approach were uneventful.My delay in running the descent check promptly as we were descending through FL180 contributed to the altitude deviation. Also; my expectation of what I should be seeing on the altimeter vs. what was actually being displayed during the 1000-to-go call also contributed to this simple mistake not being caught. The fact that the altimeter was set exactly 1 inch too high; thus causing the altitude to be off by almost exactly 1000 feet was a horrible coincidence that fed into my expectation. Another possible factor was the unusually high altimeter setting that is not typically seen may have contributed to the FO's input error. Promptly running the descent check through FL180; and certainly before any intermediate level offs; I believe; would have brought the error to light sooner. Being less complacent during the critical 1000-to-go call would also have been crucial in not allowing my expectation to cloud reality.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.