Narrative:

The captain flew the leg. During this flight; the altitude preselector/alerter (apa) started malfunctioning. The red flag was present at times; and the aural beep would go off repeatedly at random; inappropriate altitudes (as well as when it should go off.) also because of this malfunction; it would sometimes not capture the altitude on autopilot. The next leg; flown by me. The apa problem intensified a little; as it was now beeping even more often than the previous leg. During the descent phase; I decided to start hand-flying the plane because on autopilot the altitude was not capturing at all at this point. I had come close to busting altitude; so I did not want to rely on autopilot anymore. I now realize that it may have been a better idea to leave it on autopilot and capture the altitude through other means like vsi mode for example. I don't know why but at the time; I did not think of this simple alternative. About 30NM from our destination; the captain went off on comm 2 to check on our gate assignment. He came back and relayed to me that operations had told him something about repositioning the plane to the maintenance hangar. He wasn't sure (the operations radio personnel are infamous for being unable to speak english); so I asked him to call operations back and clarify what was going on with us. I wanted to know; because I was annoyed about the reposition. Right after asking him this though; I distinctly remember thinking to myself that it had not been the best idea to ask him to go back on comm 2 since we were now in the terminal area and things were starting to get busy in the cockpit. At this point; I was hand-flying the plane; working comm 1 since the captain was on comm 2; and was also conversing with the captain about what was going on with the whole gate/repo situation. Around this time; approach gave me a descent to 4;000 ft and a heading and speed restriction. I remember reminding to myself sometime during the descent to 4;000 ft that it was coming up so as not to forget it. But something(s) distracted me; and the next thing I knew; the captain was exclaiming; 'aren't we supposed to be at 4;000?!' I looked at the altimeter and I was descending through about 3;200 ft. At that exact same moment; approach called us and told us to maintain 3;000. So I continued the short descent to 3;000 ft. The rest of the flight went by without a hitch although I did notice that both the captain and I were making little mistakes like missing a radio call. I think it was because we were both shaken up about what had just happened. Essentially; I screwed up. I had known that the apa was malfunctioning; and should have taken better steps to prevent this altitude bust. As stated before; I should have left the plane on autopilot. I do hand-fly on a regular basis; but it was probably not a good idea to do it in this particular situation: in the terminal area when I got busy handling several duties at once. I certainly should not have been still using the flight director after disengaging the autopilot. I don't know why I did this; it seems so stupid to me in retrospect. I became so fixated on following the flight director that I forgot that the altitude wouldn't capture; and continued to follow it down right through the assigned altitude. In any normal situation the apa would have beeped at a thousand feet above 4;000 and also as I was descending through 4;000; but since the apa was broken; it did not give me the aural reminders. This aural reminder serves to help us; but perhaps I had gotten too used to it and this reliance fell back on me. I think another factor was the lack of the captain's leadership. It was poor decision-making on my part to turn off the autopilot; but the captain never raised any concerns either or reminded me that there were better alternatives. I don't know if this was due to the confidence that he may have had in me (which; if he did; is certainly no longer the case after this incident!); or simply because it didn't occur to him either. Regardless of whether the plane was on autopilot or hand-flown; I should have been more vigilant. I feel totally responsible for this mistake; but I think the captain should have been more vigilant as well. He was the one who caught the mistake; but I was already 800 ft off by the time he noticed. To sum it up; I think what really caused the mistake was both my captain and my bad decision-making (on several different things like not using autopilot; going off on comm 2 to discuss non-essential issues when we were in terminal area; and etc.); distractions natural to that phase of flight; and allowing myself to get distracted through lack of vigilance. I feel very fortunate that this mistake did not result in an accident. I now know through personal experience how easily something like this can happen; where both pilots miss a crucial detail. I have definitely learned several different lessons; one of which is the importance of maintaining an organized; sterile; and vigilant cockpit especially during a critical phase like approach.

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Original NASA ASRS Text

Title: A SF340 Altitude/Preselector/Alerter (APA) malfunctioned causing spurious alerts. After disconnecting the autopilot in order to disable the APA; the First Officer became distracted and during a descent failed to level at the assigned altitude while the Captain was performing pre-arrival duties.

Narrative: The Captain flew the leg. During this flight; the altitude preselector/alerter (APA) started malfunctioning. The red flag was present at times; and the aural beep would go off repeatedly at random; inappropriate altitudes (as well as when it SHOULD go off.) Also because of this malfunction; it would sometimes not capture the altitude on autopilot. The next leg; flown by me. The APA problem intensified a little; as it was now beeping even more often than the previous leg. During the descent phase; I decided to start hand-flying the plane because on autopilot the altitude was not capturing at all at this point. I had come close to busting altitude; so I did not want to rely on autopilot anymore. I now realize that it may have been a better idea to leave it on autopilot and capture the altitude through other means like VSI mode for example. I don't know why but at the time; I did not think of this simple alternative. About 30NM from our destination; the Captain went off on COMM 2 to check on our gate assignment. He came back and relayed to me that operations had told him something about repositioning the plane to the maintenance hangar. He wasn't sure (the Operations radio personnel are infamous for being unable to speak English); so I asked him to call operations back and clarify what was going on with us. I wanted to know; because I was annoyed about the reposition. Right after asking him this though; I distinctly remember thinking to myself that it had not been the best idea to ask him to go back on COMM 2 since we were now in the terminal area and things were starting to get busy in the cockpit. At this point; I was hand-flying the plane; working COMM 1 since the Captain was on COMM 2; and was also conversing with the Captain about what was going on with the whole gate/repo situation. Around this time; Approach gave me a descent to 4;000 FT and a heading and speed restriction. I remember reminding to myself sometime during the descent to 4;000 FT that it was coming up so as not to forget it. But something(s) distracted me; and the next thing I knew; the Captain was exclaiming; 'Aren't we supposed to be at 4;000?!' I looked at the altimeter and I was descending through about 3;200 FT. At that exact same moment; Approach called us and told us to maintain 3;000. So I continued the short descent to 3;000 FT. The rest of the flight went by without a hitch although I did notice that both the Captain and I were making little mistakes like missing a radio call. I think it was because we were both shaken up about what had just happened. Essentially; I screwed up. I had known that the APA was malfunctioning; and should have taken better steps to prevent this altitude bust. As stated before; I should have left the plane on autopilot. I do hand-fly on a regular basis; but it was probably not a good idea to do it in this particular situation: in the terminal area when I got busy handling several duties at once. I certainly should not have been still using the flight director after disengaging the autopilot. I don't know why I did this; it seems so stupid to me in retrospect. I became so fixated on following the flight director that I forgot that the altitude wouldn't capture; and continued to follow it down right through the assigned altitude. In any normal situation the APA would have beeped at a thousand feet above 4;000 and also as I was descending through 4;000; but since the APA was broken; it did not give me the aural reminders. This aural reminder serves to help us; but perhaps I had gotten too used to it and this reliance fell back on me. I think another factor was the lack of the Captain's leadership. It was poor decision-making on my part to turn off the autopilot; but the Captain never raised any concerns either or reminded me that there were better alternatives. I don't know if this was due to the confidence that he may have had in me (which; if he did; is certainly no longer the case after this incident!); or simply because it didn't occur to him either. Regardless of whether the plane was on autopilot or hand-flown; I should have been more vigilant. I feel totally responsible for this mistake; but I think the Captain should have been more vigilant as well. He was the one who caught the mistake; but I was already 800 FT off by the time he noticed. To sum it up; I think what really caused the mistake was both my Captain and my bad decision-making (on several different things like not using autopilot; going off on COMM 2 to discuss non-essential issues when we were in terminal area; and etc.); distractions natural to that phase of flight; and allowing myself to get distracted through lack of vigilance. I feel very fortunate that this mistake did not result in an accident. I now know through personal experience how easily something like this can happen; where both pilots miss a crucial detail. I have definitely learned several different lessons; one of which is the importance of maintaining an organized; sterile; and vigilant cockpit especially during a critical phase like approach.

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.