Narrative:

On arrival into the new york area on the korry 3 arrival; we were inside korry; we were given a 120 degree heading; and slowed to 210 KTS for spacing. Then the controller gave us a descent from 10;000 ft to 8;000 ft for traffic. I was the pilot monitoring; so I read back; 'roger; descend and maintain 8;000 ft for traffic.' I followed the company procedure; reset the altitude alerter; saw 8;000 ft annunciated in the lights; put my left pointer finger on the screw next to the altitude alerter and announced; '8;000 ft; set and armed' and the captain replied; 'roger; 8000 ft' to me. I am 100% positive that 8;000 ft was set in the window. I can still see it in my mind's eye. As the captain began our descent; I continued getting the airplane ready for our arrival by tuning the radios in #2 for operations and setting the lga VOR frequency on my side for the anticipated as usual; direct lga we usually receive. It is my firm belief that when I tuned in the lga VOR with my left hand; the pinky finger made positive contact with the altitude alerter knob and rolled the altitude down 1;000 ft to 7;000 ft. The next day; I flew the same trip; and while on the ground; I was able to do just as I described above with very little pressure from my pinky finger on the knob. By rotating the VOR knob clockwise; my pinky finger slides under the altitude knob and rolls it counterclockwise; which clicks down the altitude 1;000 ft with what seems like less than a few millimeters of subtle movement. I repeated this several times and decided it was a significant discovery. I have 7;500 hours on this airplane and can recall several times where the altitude was somehow changed without explanation. The difference was I caught it those times. The captain was flying the airplane and began the descent. At some point; the altitude was changed. Going through 7;500 ft; the controller said; 'aircraft X; return to 8;000 ft.' and I said; 'roger; leaving 7;300 ft climbing to 8;000 ft.' I did not remember being cleared to 7;000 ft; and had a bad feeling. The controller did not say anything at the time. We did not have an RA or TA. I did not see another aircraft on TCAS; because I looked there immediately because I remembered the clearance to 8;000 ft was for traffic. When I called TRACON per their request; I told the controller I felt bad about what happened; and that I had a theory about the altitude alert knob. After this; I realize the altitude knob needs to be more difficult to turn; or relocated; or something. I too am at fault. I should have never let the captain descend the airplane below 7;000 ft. The alerter issue is no excuse. I needed to carefully monitor the captain's descent and I failed to do so. I let myself get busy doing other things; depending on automation; and I know better. Perhaps fatigue is a contributing factor. I wanted a cup of coffee 30 minutes prior to the arrival; but never drink coffee this late because I can't get to sleep; which makes me tired for the trip the next night. It was the end of a long day in the seat of an MD80; schedule for 7 hours 45 minutes in the seat. Since this is something I have seen in the past and prevented it from happening; I think fatigue is a factor. I thought about this for hours after it happened; and spoke to several other MD80 pilots about the altitude alerter; and they all told me that they have experienced similar 'uncommanded altitude alerter changes' in their flight careers. Maybe now we have a clue as to how it happened.

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Original NASA ASRS Text

Title: MD80 First Officer reports an altitude deviation he believed to have been caused by his inadvertent change of the altitude alert setting when he tuned the VOR.

Narrative: On arrival into the New York area on the KORRY 3 arrival; we were inside KORRY; we were given a 120 degree heading; and slowed to 210 KTS for spacing. Then the Controller gave us a descent from 10;000 FT to 8;000 FT for traffic. I was the Pilot Monitoring; so I read back; 'Roger; descend and maintain 8;000 FT for traffic.' I followed the company procedure; reset the altitude alerter; saw 8;000 FT annunciated in the lights; put my left pointer finger on the screw next to the altitude alerter and announced; '8;000 FT; set and armed' and the Captain replied; 'Roger; 8000 FT' to me. I am 100% positive that 8;000 FT was set in the window. I can still see it in my mind's eye. As the Captain began our descent; I continued getting the airplane ready for our arrival by tuning the radios in #2 for operations and setting the LGA VOR frequency on my side for the anticipated as usual; direct LGA we usually receive. It is my firm belief that when I tuned in the LGA VOR with my left hand; the pinky finger made positive contact with the altitude alerter knob and rolled the altitude down 1;000 FT to 7;000 FT. The next day; I flew the same trip; and while on the ground; I was able to do just as I described above with very little pressure from my pinky finger on the knob. By rotating the VOR knob clockwise; my pinky finger slides under the altitude knob and rolls it counterclockwise; which clicks down the altitude 1;000 FT with what seems like less than a few millimeters of subtle movement. I repeated this several times and decided it was a significant discovery. I have 7;500 hours on this airplane and can recall several times where the altitude was somehow changed without explanation. The difference was I caught it those times. The Captain was flying the airplane and began the descent. At some point; the altitude was changed. Going through 7;500 FT; the Controller said; 'Aircraft X; return to 8;000 FT.' And I said; 'Roger; leaving 7;300 FT climbing to 8;000 FT.' I did not remember being cleared to 7;000 FT; and had a bad feeling. The Controller did not say anything at the time. We did not have an RA or TA. I did not see another aircraft on TCAS; because I looked there immediately because I remembered the clearance to 8;000 FT was for traffic. When I called TRACON per their request; I told the Controller I felt bad about what happened; and that I had a theory about the altitude alert knob. After this; I realize the altitude knob needs to be more difficult to turn; or relocated; or something. I too am at fault. I should have never let the Captain descend the airplane below 7;000 FT. The alerter issue is no excuse. I needed to carefully monitor the Captain's descent and I failed to do so. I let myself get busy doing other things; depending on automation; and I know better. Perhaps fatigue is a contributing factor. I wanted a cup of coffee 30 minutes prior to the arrival; but never drink coffee this late because I can't get to sleep; which makes me tired for the trip the next night. It was the end of a long day in the seat of an MD80; schedule for 7 hours 45 minutes in the seat. Since this is something I have seen in the past and prevented it from happening; I think fatigue is a factor. I thought about this for hours after it happened; and spoke to several other MD80 pilots about the altitude alerter; and they all told me that they have experienced similar 'uncommanded altitude alerter changes' in their flight careers. Maybe now we have a clue as to how it happened.

Data retrieved from NASA's ASRS site as of April 2012 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.