Narrative:

The flight segment from detroit to saginaw was a short 20 mins, which entailed a high cockpit workload. The approach check was to be accomplished immediately after the climb check. In addition we were navigating around heavy rain showers. As the non-flying first officer, I was performing my duties, communicate with ATC, ATC, company call, P/a and all items required for our approach. Saginaw approach cleared us to 11000' MSL which I dialed into the altitude alerter. Shortly before that clearance was received the captain had read the ATIS and learned it would be an ILS 5 at saginaw. He then began to look in his airport manual for the chart. At 12000' I made the required altitude awareness call, '1 to go,' and the captain acknowledged. He returned his attention to the airport book to retrieve the approach chart and discovered he did not have an ILS 5 chart for saginaw and asked me for my copy. I turned my attention to my airport book to remove the chart when I heard the altitude alerter sound. I quickly looked up to see we were slowly descending through 10400' and pointed to the alerter and replied, 'we're at 11.' then ATC called for us to confirm our altitude. The captain promptly turned off the transponder, climbed to 11000' and directed me to reply '1-1-thousand' to ATC. After a brief pause I did reply. At 11000' the captain turned the transponder back on and directed me to reply, 'we switched to our #2 transponder--what do you show now?' ATC replied 10800' when we were level at 11000'. The following approach and landing was routine. We were the only aircraft in the area and there was no conflict. The captain wrote up the encoder as being erroneous. At the time of the incident, I remembered feeling angry at the captain for letting me down. Why did he continue to look for his chart inside of the 1000' callout when he asked me for my copy. It was leg and I assumed he was flying the aircraft. For that moment nobody was. A moment is all it takes. At the same time I realized our roles could have been reversed and it could have been me. I also realize there is more than 1 pilot so that we can backup and check each other for a safer operation. At the same time, there is more than 1 pilot because there are more duties than 1 pilot can handle. For example, the situation when 1 crew member is flying and communicating with ATC and the other is off getting ATIS. One guy miss-hears an altitude, then busts while the other is out of the loop for back up.

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Original NASA ASRS Text

Title: ACR MLG ALT DEVIATION OVERSHOT DURING DESCENT THEN TURNED OFF MODE C TO COVER ERROR.

Narrative: THE FLT SEGMENT FROM DETROIT TO SAGINAW WAS A SHORT 20 MINS, WHICH ENTAILED A HIGH COCKPIT WORKLOAD. THE APCH CHK WAS TO BE ACCOMPLISHED IMMEDIATELY AFTER THE CLB CHK. IN ADDITION WE WERE NAVIGATING AROUND HEAVY RAIN SHOWERS. AS THE NON-FLYING F/O, I WAS PERFORMING MY DUTIES, COMMUNICATE WITH ATC, ATC, COMPANY CALL, P/A AND ALL ITEMS REQUIRED FOR OUR APCH. SAGINAW APCH CLRED US TO 11000' MSL WHICH I DIALED INTO THE ALT ALERTER. SHORTLY BEFORE THAT CLRNC WAS RECEIVED THE CAPT HAD READ THE ATIS AND LEARNED IT WOULD BE AN ILS 5 AT SAGINAW. HE THEN BEGAN TO LOOK IN HIS ARPT MANUAL FOR THE CHART. AT 12000' I MADE THE REQUIRED ALT AWARENESS CALL, '1 TO GO,' AND THE CAPT ACKNOWLEDGED. HE RETURNED HIS ATTN TO THE ARPT BOOK TO RETRIEVE THE APCH CHART AND DISCOVERED HE DID NOT HAVE AN ILS 5 CHART FOR SAGINAW AND ASKED ME FOR MY COPY. I TURNED MY ATTN TO MY ARPT BOOK TO REMOVE THE CHART WHEN I HEARD THE ALT ALERTER SOUND. I QUICKLY LOOKED UP TO SEE WE WERE SLOWLY DSNDING THROUGH 10400' AND POINTED TO THE ALERTER AND REPLIED, 'WE'RE AT 11.' THEN ATC CALLED FOR US TO CONFIRM OUR ALT. THE CAPT PROMPTLY TURNED OFF THE XPONDER, CLBED TO 11000' AND DIRECTED ME TO REPLY '1-1-THOUSAND' TO ATC. AFTER A BRIEF PAUSE I DID REPLY. AT 11000' THE CAPT TURNED THE XPONDER BACK ON AND DIRECTED ME TO REPLY, 'WE SWITCHED TO OUR #2 XPONDER--WHAT DO YOU SHOW NOW?' ATC REPLIED 10800' WHEN WE WERE LEVEL AT 11000'. THE FOLLOWING APCH AND LNDG WAS ROUTINE. WE WERE THE ONLY ACFT IN THE AREA AND THERE WAS NO CONFLICT. THE CAPT WROTE UP THE ENCODER AS BEING ERRONEOUS. AT THE TIME OF THE INCIDENT, I REMEMBERED FEELING ANGRY AT THE CAPT FOR LETTING ME DOWN. WHY DID HE CONTINUE TO LOOK FOR HIS CHART INSIDE OF THE 1000' CALLOUT WHEN HE ASKED ME FOR MY COPY. IT WAS LEG AND I ASSUMED HE WAS FLYING THE ACFT. FOR THAT MOMENT NOBODY WAS. A MOMENT IS ALL IT TAKES. AT THE SAME TIME I REALIZED OUR ROLES COULD HAVE BEEN REVERSED AND IT COULD HAVE BEEN ME. I ALSO REALIZE THERE IS MORE THAN 1 PLT SO THAT WE CAN BACKUP AND CHK EACH OTHER FOR A SAFER OPERATION. AT THE SAME TIME, THERE IS MORE THAN 1 PLT BECAUSE THERE ARE MORE DUTIES THAN 1 PLT CAN HANDLE. FOR EXAMPLE, THE SITUATION WHEN 1 CREW MEMBER IS FLYING AND COMMUNICATING WITH ATC AND THE OTHER IS OFF GETTING ATIS. ONE GUY MISS-HEARS AN ALT, THEN BUSTS WHILE THE OTHER IS OUT OF THE LOOP FOR BACK UP.

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.