Autoflt fails to capture altitude and crew does not notice when distraction outside the cockpit.

Attributes
ACN	449830
Time
Date	199909
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : grr.airport
State Reference	MI
Altitude	msl bound lower : 8500 msl bound upper : 9000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zob.artcc tracon : grr.tracon
Operator	common carrier : air taxi
Make Model Name	MU-2 Undifferentiated or Other Model
Operating Under FAR Part	Part 135
Navigation In Use	Other
Flight Phase	descent : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	company : air taxi
Function	flight crew : captain oversight : pic
Qualification	pilot : cfi pilot : atp pilot : multi engine pilot : commercial
Experience	flight time last 90 days : 105 flight time total : 5512 flight time type : 20
ASRS Report	449830
Person 2
Affiliation	company : air taxi
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial pilot : multi engine
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : overshoot non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to assigned altitude
Supplementary
Problem Areas	Aircraft Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

During a descent into grr we were cleared to descend to 9000 ft. 9000 ft was set in the altitude selector and armed on the autoplt control panel. Shortly after this we were handed off to grr approach. At this time my first officer reported to me that he had the field in sight. I then began looking for the airport. When I looked back in the cockpit, we were descending through 8500 ft. The altitude alert light on the altimeter was lit, however, the altitude arm light was still on on the autoplt control panel and the autoplt did not capture the altitude. At this point, I disengaged the autoplt and immediately climbed back to 9000 ft. Total time off altitude was about 40 seconds. Once back at 9000 ft, the first officer called grr approach. Grr then gave us a descent to the airport and did not question any deviation. I believe the contributing factors were the autoplt's failure to capture the altitude along with my failure to monitor the automation as we were approaching the assigned altitude. In the future, I will monitor the automation more closely -- even in VMC. Particularly when approaching assigned altitudes and headings. If I wished to look for the airport, I should have the first officer monitor the instruments. This procedure is used on instrument approachs, but should also be used during visual conditions.

Original NASA ASRS Text

Title: AUTOFLT FAILS TO CAPTURE ALT AND CREW DOES NOT NOTICE WHEN DISTR OUTSIDE THE COCKPIT.

Narrative: DURING A DSCNT INTO GRR WE WERE CLRED TO DSND TO 9000 FT. 9000 FT WAS SET IN THE ALT SELECTOR AND ARMED ON THE AUTOPLT CTL PANEL. SHORTLY AFTER THIS WE WERE HANDED OFF TO GRR APCH. AT THIS TIME MY FO RPTED TO ME THAT HE HAD THE FIELD IN SIGHT. I THEN BEGAN LOOKING FOR THE ARPT. WHEN I LOOKED BACK IN THE COCKPIT, WE WERE DSNDING THROUGH 8500 FT. THE ALT ALERT LIGHT ON THE ALTIMETER WAS LIT, HOWEVER, THE ALT ARM LIGHT WAS STILL ON ON THE AUTOPLT CTL PANEL AND THE AUTOPLT DID NOT CAPTURE THE ALT. AT THIS POINT, I DISENGAGED THE AUTOPLT AND IMMEDIATELY CLBED BACK TO 9000 FT. TOTAL TIME OFF ALT WAS ABOUT 40 SECONDS. ONCE BACK AT 9000 FT, THE FO CALLED GRR APCH. GRR THEN GAVE US A DSCNT TO THE ARPT AND DID NOT QUESTION ANY DEV. I BELIEVE THE CONTRIBUTING FACTORS WERE THE AUTOPLT'S FAILURE TO CAPTURE THE ALT ALONG WITH MY FAILURE TO MONITOR THE AUTOMATION AS WE WERE APCHING THE ASSIGNED ALT. IN THE FUTURE, I WILL MONITOR THE AUTOMATION MORE CLOSELY -- EVEN IN VMC. PARTICULARLY WHEN APCHING ASSIGNED ALTS AND HDGS. IF I WISHED TO LOOK FOR THE ARPT, I SHOULD HAVE THE FO MONITOR THE INSTS. THIS PROC IS USED ON INST APCHS, BUT SHOULD ALSO BE USED DURING VISUAL CONDITIONS.

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.