A dehavilland-8-200 in climb at 7000 ft received an ADI aural mismatch warning. Attempting to solve mismatch incurred altitude excursion.

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Attributes
ACN	594237
Time
Date	200309
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	msl bound lower : 7000 msl bound upper : 7400
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : zzz.tracon
Operator	common carrier : air carrier
Make Model Name	Dash 8-200
Operating Under FAR Part	Part 121
Flight Phase	climbout : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : cfi
Experience	flight time last 90 days : 200 flight time total : 7500 flight time type : 400
ASRS Report	594237
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : aural warning other flight crewa other flight crewb
Resolutory Action	flight crew : returned to assigned altitude flight crew : overcame equipment problem
Consequence	other
Supplementary
Problem Areas	Flight Crew Human Performance Environmental Factor Aircraft
Primary Problem	Flight Crew Human Performance

Narrative:

Scheduled far .121 flight from ZZZ to ZZZ1. WX was perfectly clear with unlimited visibility, and 2 capts were paired (flying) together. On climb out from ZZZ, we received an 'ADI bell mismatch' warning. Both of us (I was in the left seat) immediately went into our problem-solving mode and determined that it was the #2 ADI that was in error (we compared the #1 ADI, #2 ADI, and standby ADI). Unfortunately, in our haste to solve our problem, we lost our common sense and nobody was flying the airplane. The autoplt disconnect when the original 'ADI bell mismatch' warning annunciated. However, neither of us noticed there is no aural warning of an autoplt disconnect -- only a visual annunciator, which neither of us noticed while trying to solve our problem. The end result was the airplane climbed through our assigned altitude at 7000 ft. We leveled off at 7400 ft and immediately descended back to 7000 ft. I checked the TCASII -- no conflict, and the controller said nothing.

Original NASA ASRS Text

Title: A DEHAVILLAND-8-200 IN CLB AT 7000 FT RECEIVED AN ADI AURAL MISMATCH WARNING. ATTEMPTING TO SOLVE MISMATCH INCURRED ALT EXCURSION.

Narrative: SCHEDULED FAR .121 FLT FROM ZZZ TO ZZZ1. WX WAS PERFECTLY CLR WITH UNLIMITED VISIBILITY, AND 2 CAPTS WERE PAIRED (FLYING) TOGETHER. ON CLBOUT FROM ZZZ, WE RECEIVED AN 'ADI BELL MISMATCH' WARNING. BOTH OF US (I WAS IN THE L SEAT) IMMEDIATELY WENT INTO OUR PROB-SOLVING MODE AND DETERMINED THAT IT WAS THE #2 ADI THAT WAS IN ERROR (WE COMPARED THE #1 ADI, #2 ADI, AND STANDBY ADI). UNFORTUNATELY, IN OUR HASTE TO SOLVE OUR PROB, WE LOST OUR COMMON SENSE AND NOBODY WAS FLYING THE AIRPLANE. THE AUTOPLT DISCONNECT WHEN THE ORIGINAL 'ADI BELL MISMATCH' WARNING ANNUNCIATED. HOWEVER, NEITHER OF US NOTICED THERE IS NO AURAL WARNING OF AN AUTOPLT DISCONNECT -- ONLY A VISUAL ANNUNCIATOR, WHICH NEITHER OF US NOTICED WHILE TRYING TO SOLVE OUR PROB. THE END RESULT WAS THE AIRPLANE CLBED THROUGH OUR ASSIGNED ALT AT 7000 FT. WE LEVELED OFF AT 7400 FT AND IMMEDIATELY DSNDED BACK TO 7000 FT. I CHKED THE TCASII -- NO CONFLICT, AND THE CTLR SAID NOTHING.

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.