An atx aircraft has its autoplt disconnect on leveloff at 11000 ft. The crew fails to hear the disconnect chime and the aircraft bottoms out at 10200 ft before ATC calls them.

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Attributes
ACN	406090
Time
Date	199806
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : ape
State Reference	OH
Altitude	msl bound lower : 10200 msl bound upper : 11000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zid
Operator	common carrier : air taxi
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	Part 135
Flight Phase	cruise other descent other
Flight Plan	IFR
Person 1
Affiliation	company : air taxi
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 180 flight time total : 10500 flight time type : 900
ASRS Report	406090
Person 2
Affiliation	company : air taxi
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude inflight encounter : weather non adherence : clearance other anomaly other
Independent Detector	other controllera
Resolutory Action	flight crew : returned to intended course or assigned course other
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation other

Narrative:

We were given a descent to 11000 ft. We were operating on the autoplt while descending and working our way around thunderstorms. After leveloff at 11000 ft, autoplt disengaged and aircraft lost approximately 500-800 ft. Center advised us to say assigned altitude. We relayed 11000 ft and climbed back to assigned altitude. We had been having problems with autoplt disengagements earlier that day. The combination of the WX, turbulence, rain and noise level allowed the autoplt to disengage while not hearing the chime disconnect thereby causing the problem.

Original NASA ASRS Text

Title: AN ATX ACFT HAS ITS AUTOPLT DISCONNECT ON LEVELOFF AT 11000 FT. THE CREW FAILS TO HEAR THE DISCONNECT CHIME AND THE ACFT BOTTOMS OUT AT 10200 FT BEFORE ATC CALLS THEM.

Narrative: WE WERE GIVEN A DSCNT TO 11000 FT. WE WERE OPERATING ON THE AUTOPLT WHILE DSNDING AND WORKING OUR WAY AROUND TSTMS. AFTER LEVELOFF AT 11000 FT, AUTOPLT DISENGAGED AND ACFT LOST APPROX 500-800 FT. CTR ADVISED US TO SAY ASSIGNED ALT. WE RELAYED 11000 FT AND CLBED BACK TO ASSIGNED ALT. WE HAD BEEN HAVING PROBS WITH AUTOPLT DISENGAGEMENTS EARLIER THAT DAY. THE COMBINATION OF THE WX, TURB, RAIN AND NOISE LEVEL ALLOWED THE AUTOPLT TO DISENGAGE WHILE NOT HEARING THE CHIME DISCONNECT THEREBY CAUSING THE PROB.

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.