MD90 crew loses altitude while troubleshooting autoplt trim failure.

Attributes
ACN	719974
Time
Date	200612
Local Time Of Day	1801 To 2400
Place
Locale Reference	intersection : siler
State Reference	TX
Altitude	msl single value : 11000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : d10.tracon
Operator	common carrier : air carrier
Make Model Name	MD-90 Series (DC-9-90) Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	descent : approach
Route In Use	arrival star : bowie
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 210 flight time total : 13000 flight time type : 1400
ASRS Report	719974
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : multi engine pilot : instrument pilot : flight engineer
Experience	flight time last 90 days : 200 flight time total : 800 flight time type : 5000
ASRS Report	719900
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other controllera other flight crewa
Resolutory Action	controller : issued alert flight crew : returned to assigned altitude
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft
Primary Problem	Ambiguous

Narrative:

On the bowie 8 arrival to dfw. While troubleshooting an autoplt discrepancy; the autoplt did an uncommanded descent to 10600 ft. We caught the descent right away. ATC instructed us to climb back to 11000 ft. Factor was distraction due to troubleshooting problem. I should have continued to fly/monitor the aircraft while the first officer worked the problem. 719900: aircraft was having a trim (electric) problem. Autoplt was selected 'off' because autoplt would not hold altitude correctly. When autoplt disconnected with aircraft out of trim; the nose pitched down and began an uncommanded descent. Aircraft descended approximately 500 ft before we were able to arrest descent. Factors were that there is no indication that the MD88 has no annunciator to indicate that the autoplt was having difficulty trimming the aircraft. Also reduced situational awareness due to loud wind noise in aircraft; reaching target speeds and altitudes on the bowie 8 arrival and the troubleshooting the problem with both the autoplt and alternate trim not on.

Original NASA ASRS Text

Title: MD90 CREW LOSES ALT WHILE TROUBLESHOOTING AUTOPLT TRIM FAILURE.

Narrative: ON THE BOWIE 8 ARR TO DFW. WHILE TROUBLESHOOTING AN AUTOPLT DISCREPANCY; THE AUTOPLT DID AN UNCOMMANDED DSCNT TO 10600 FT. WE CAUGHT THE DSCNT RIGHT AWAY. ATC INSTRUCTED US TO CLB BACK TO 11000 FT. FACTOR WAS DISTR DUE TO TROUBLESHOOTING PROB. I SHOULD HAVE CONTINUED TO FLY/MONITOR THE ACFT WHILE THE FO WORKED THE PROB. 719900: ACFT WAS HAVING A TRIM (ELECTRIC) PROB. AUTOPLT WAS SELECTED 'OFF' BECAUSE AUTOPLT WOULD NOT HOLD ALT CORRECTLY. WHEN AUTOPLT DISCONNECTED WITH ACFT OUT OF TRIM; THE NOSE PITCHED DOWN AND BEGAN AN UNCOMMANDED DSCNT. ACFT DSNDED APPROX 500 FT BEFORE WE WERE ABLE TO ARREST DSCNT. FACTORS WERE THAT THERE IS NO INDICATION THAT THE MD88 HAS NO ANNUNCIATOR TO INDICATE THAT THE AUTOPLT WAS HAVING DIFFICULTY TRIMMING THE ACFT. ALSO REDUCED SITUATIONAL AWARENESS DUE TO LOUD WIND NOISE IN ACFT; REACHING TARGET SPDS AND ALTS ON THE BOWIE 8 ARR AND THE TROUBLESHOOTING THE PROB WITH BOTH THE AUTOPLT AND ALTERNATE TRIM NOT ON.

Data retrieved from NASA's ASRS site as of January 2009 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.