Narrative:

While being vectored for sequencing, we were issued a descent clearance from 8000' to a lower altitude. I began descending and noticed that the altitude alert still had the previous altitude set in. The captain had read back our descent altitude but neglected to set it in the altitude alert. Upon noticing this, I asked the captain if we weren't cleared to 5000'. He answered in the affirmative, so I reset the altitude alert to 5000' and continued the descent. Approach control called and said we'd get a lower altitude when we clear traffic below...while he was explaining this, he stopped short and asked what our altitude was. The captain replied that we were about to pass through 6000' en route to 5000'. The controller said that the descent clearance was only to 7000'. At this point we noticed an mdt Y pass below at about 5000'. I stopped the descent as the controller called the mdt Y at 11 O'clock and the captain replied that the traffic was in sight. After clearing the mdt Y we were then cleared for the ILS 22R approach. Reflecting on the chain of events, I think that: 1) when noticing that the altitude alert was not properly set, I should not have suggested an altitude to the captain, but rather asked what altitude we were cleared to. This may have made him stop and think or even ask ATC to confirm the altitude. 2) the pilot responsible for setting the altitude alert should discipline themselves to set it immediately, instead of relying on one's memory to set it 30 seconds later.

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Original NASA ASRS Text

Title: ACR DESCENDING, MISUNDERSTANDS ALT CLRNC, DESCENDS BELOW ASSIGNED ALT.

Narrative: WHILE BEING VECTORED FOR SEQUENCING, WE WERE ISSUED A DSNT CLRNC FROM 8000' TO A LOWER ALT. I BEGAN DESCENDING AND NOTICED THAT THE ALT ALERT STILL HAD THE PREVIOUS ALT SET IN. THE CAPT HAD READ BACK OUR DSNT ALT BUT NEGLECTED TO SET IT IN THE ALT ALERT. UPON NOTICING THIS, I ASKED THE CAPT IF WE WEREN'T CLRED TO 5000'. HE ANSWERED IN THE AFFIRMATIVE, SO I RESET THE ALT ALERT TO 5000' AND CONTINUED THE DSNT. APCH CTL CALLED AND SAID WE'D GET A LOWER ALT WHEN WE CLEAR TFC BELOW...WHILE HE WAS EXPLAINING THIS, HE STOPPED SHORT AND ASKED WHAT OUR ALT WAS. THE CAPT REPLIED THAT WE WERE ABOUT TO PASS THROUGH 6000' ENRTE TO 5000'. THE CTLR SAID THAT THE DSNT CLRNC WAS ONLY TO 7000'. AT THIS POINT WE NOTICED AN MDT Y PASS BELOW AT ABOUT 5000'. I STOPPED THE DSNT AS THE CTLR CALLED THE MDT Y AT 11 O'CLOCK AND THE CAPT REPLIED THAT THE TFC WAS IN SIGHT. AFTER CLEARING THE MDT Y WE WERE THEN CLRED FOR THE ILS 22R APCH. REFLECTING ON THE CHAIN OF EVENTS, I THINK THAT: 1) WHEN NOTICING THAT THE ALT ALERT WAS NOT PROPERLY SET, I SHOULD NOT HAVE SUGGESTED AN ALT TO THE CAPT, BUT RATHER ASKED WHAT ALT WE WERE CLRED TO. THIS MAY HAVE MADE HIM STOP AND THINK OR EVEN ASK ATC TO CONFIRM THE ALT. 2) THE PLT RESPONSIBLE FOR SETTING THE ALT ALERT SHOULD DISCIPLINE THEMSELVES TO SET IT IMMEDIATELY, INSTEAD OF RELYING ON ONE'S MEMORY TO SET IT 30 SECONDS LATER.

Data retrieved from NASA's ASRS site as of July 2007 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.