Altitude deviation altitude overshot. Cpr aircraft in a high rate descent has the altitude capture mode of the autoplt malfunction and before the flight crew reacted the aircraft went below the assigned altitude.

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Attributes
ACN	307920
Time
Date	199506
Day	Wed
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : har
State Reference	PA
Altitude	msl bound lower : 9700 msl bound upper : 10000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zny
Operator	general aviation : corporate
Make Model Name	IAI1124/1124A/Westwind
Operating Under FAR Part	Part 91
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : cfi pilot : atp pilot : commercial pilot : instrument
Experience	flight time last 90 days : 90 flight time total : 7900 flight time type : 2400
ASRS Report	307950
Person 2
Affiliation	Other
Function	flight crew : first officer
Qualification	pilot : commercial pilot : atp pilot : instrument
Experience	flight time last 90 days : 80 flight time total : 14000 flight time type : 300
ASRS Report	307776
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude altitude deviation : overshoot non adherence : clearance
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Center had cleared us to descend to 10000 ft. I pushed my altitude preselect, but it failed to activate. We were having quite a bit of fluctuation in the #1 CDI and I was paying more attention to the needle than I was on my altitude and deviated 300 ft below my assigned altitude. I corrected immediately to my assigned altitude. Nothing was said by center. Failure to correctly activate altitude preselect and monitor altitude will be corrected. Callback conversation with reporter revealed the following information: the captain of this westwind 1124 says that the altitude capture, altitude hold, functions of the autoplt are unreliable. He now does not trust the system and he has changed his operating procedures to insure of no future misadventures. In fact, he now demonstrates these unreliable traits to his first officer's. He has not heard from the FAA concerning this excursion.

Original NASA ASRS Text

Title: ALTDEV ALT OVERSHOT. CPR ACFT IN A HIGH RATE DSCNT HAS THE ALT CAPTURE MODE OF THE AUTOPLT MALFUNCTION AND BEFORE THE FLC REACTED THE ACFT WENT BELOW THE ASSIGNED ALT.

Narrative: CTR HAD CLRED US TO DSND TO 10000 FT. I PUSHED MY ALT PRESELECT, BUT IT FAILED TO ACTIVATE. WE WERE HAVING QUITE A BIT OF FLUCTUATION IN THE #1 CDI AND I WAS PAYING MORE ATTN TO THE NEEDLE THAN I WAS ON MY ALT AND DEVIATED 300 FT BELOW MY ASSIGNED ALT. I CORRECTED IMMEDIATELY TO MY ASSIGNED ALT. NOTHING WAS SAID BY CTR. FAILURE TO CORRECTLY ACTIVATE ALT PRESELECT AND MONITOR ALT WILL BE CORRECTED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE CAPT OF THIS WESTWIND 1124 SAYS THAT THE ALT CAPTURE, ALT HOLD, FUNCTIONS OF THE AUTOPLT ARE UNRELIABLE. HE NOW DOES NOT TRUST THE SYS AND HE HAS CHANGED HIS OPERATING PROCS TO INSURE OF NO FUTURE MISADVENTURES. IN FACT, HE NOW DEMONSTRATES THESE UNRELIABLE TRAITS TO HIS FO'S. HE HAS NOT HEARD FROM THE FAA CONCERNING THIS EXCURSION.

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.