Narrative:

Captain was flying the aircraft to dsm. We had been slowed to 250 KTS and vectored approximately 30 degrees left of course by chicago center just prior to handoff to dsm approach control. After checking with approach, we were advised that we would follow an large transport northeast of dsm. We did not see the traffic, although the WX was clear. We were given a clearance to descend to 6000'. I called leaving 7000' for 6000 to the captain, later observing him slowing his descent to level off at 6000'. I then looked down to my right to review the approach plate and identify the ADF. While looking T the approach plate, the controller advised our traffic was T 2 O'clock and I looked to the right for the traffic. While looking out the window I heard the captain say, 'what altitude should we be at?' I immediately said 6000' (6000' was set in the altitude alerter), and noted we were at approximately 5200' MSL. Captain applied thrust and climbed to 6000' and said that he didn't hear altitude alert bell or get an altitude warning light. I'm not sure if he was looking for the traffic and missed the level off at 6000', or if he thought he was cleared to a lower altitude. Contributing and corrective factors: our airline mixes flying of all medium large transport models from -10 to -83's. Some altitude alert bells are hard to hear and much inferior to the aural voice alert on -80 aircraft. I think an aural alert would have prevented this deviation (my previous trips were in -80 models). Perhaps the alerter in this aircraft didn't ring the bell, as neither pilot heard it; however, flying aircraft with different types of alerters compounds the problem, as I was conditioned to the other type of alert system by my recent trips in -80 aircraft. This aircraft was on older -30 model. Perhaps the external pressure of events happening at our financially troubled company had distracted the captain during this routine level off maneuver and he just wasn't concentrating on the situation. Supplemental information from acn 141802: did not hear the alerter bell because of conversation about traffic. Did not see the alerter light because we were looking for the traffic.

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Original NASA ASRS Text

Title: ACR MLG ALT DEVIATION OVERSHOT DURING DESCENT INTO DSM.

Narrative: CAPT WAS FLYING THE ACFT TO DSM. WE HAD BEEN SLOWED TO 250 KTS AND VECTORED APPROX 30 DEGS LEFT OF COURSE BY CHICAGO CENTER JUST PRIOR TO HDOF TO DSM APCH CTL. AFTER CHECKING WITH APCH, WE WERE ADVISED THAT WE WOULD FOLLOW AN LGT NE OF DSM. WE DID NOT SEE THE TFC, ALTHOUGH THE WX WAS CLEAR. WE WERE GIVEN A CLRNC TO DSND TO 6000'. I CALLED LEAVING 7000' FOR 6000 TO THE CAPT, LATER OBSERVING HIM SLOWING HIS DSNT TO LEVEL OFF AT 6000'. I THEN LOOKED DOWN TO MY RIGHT TO REVIEW THE APCH PLATE AND IDENT THE ADF. WHILE LOOKING T THE APCH PLATE, THE CTLR ADVISED OUR TFC WAS T 2 O'CLOCK AND I LOOKED TO THE RIGHT FOR THE TFC. WHILE LOOKING OUT THE WINDOW I HEARD THE CAPT SAY, 'WHAT ALT SHOULD WE BE AT?' I IMMEDIATELY SAID 6000' (6000' WAS SET IN THE ALT ALERTER), AND NOTED WE WERE AT APPROX 5200' MSL. CAPT APPLIED THRUST AND CLBED TO 6000' AND SAID THAT HE DIDN'T HEAR ALT ALERT BELL OR GET AN ALT WARNING LIGHT. I'M NOT SURE IF HE WAS LOOKING FOR THE TFC AND MISSED THE LEVEL OFF AT 6000', OR IF HE THOUGHT HE WAS CLRED TO A LOWER ALT. CONTRIBUTING AND CORRECTIVE FACTORS: OUR AIRLINE MIXES FLYING OF ALL MLG MODELS FROM -10 TO -83'S. SOME ALT ALERT BELLS ARE HARD TO HEAR AND MUCH INFERIOR TO THE AURAL VOICE ALERT ON -80 ACFT. I THINK AN AURAL ALERT WOULD HAVE PREVENTED THIS DEVIATION (MY PREVIOUS TRIPS WERE IN -80 MODELS). PERHAPS THE ALERTER IN THIS ACFT DIDN'T RING THE BELL, AS NEITHER PLT HEARD IT; HOWEVER, FLYING ACFT WITH DIFFERENT TYPES OF ALERTERS COMPOUNDS THE PROB, AS I WAS CONDITIONED TO THE OTHER TYPE OF ALERT SYS BY MY RECENT TRIPS IN -80 ACFT. THIS ACFT WAS ON OLDER -30 MODEL. PERHAPS THE EXTERNAL PRESSURE OF EVENTS HAPPENING AT OUR FINANCIALLY TROUBLED COMPANY HAD DISTRACTED THE CAPT DURING THIS ROUTINE LEVEL OFF MANEUVER AND HE JUST WASN'T CONCENTRATING ON THE SITUATION. SUPPLEMENTAL INFO FROM ACN 141802: DID NOT HEAR THE ALERTER BELL BECAUSE OF CONVERSATION ABOUT TFC. DID NOT SEE THE ALERTER LIGHT BECAUSE WE WERE LOOKING FOR THE TFC.

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.