MD88 overshot 10000 ft in descent.

Attributes
ACN	349000
Time
Date	199610
Day	Fri
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : hec airport : sna
State Reference	CA
Altitude	msl bound lower : 9600 msl bound upper : 10000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : lax
Operator	common carrier : air carrier
Make Model Name	MD-88
Operating Under FAR Part	Part 121
Navigation In Use	Other
Flight Phase	cruise other descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 100 flight time total : 11000 flight time type : 3000
ASRS Report	349000
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 100 flight time total : 8000 flight time type : 1500
ASRS Report	348996
Events
Anomaly	altitude deviation : overshoot non adherence : clearance
Independent Detector	aircraft equipment other aircraft equipment : unspecified
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:

We were cleared to descend from FL240 to 10000 ft on the eastside 1 arrival into sna. Descent was initiated in the 'VNAV' mode of autoflt and changed to 'IAS' during the descent. As I recall, this was done around 15000 ft MSL. Cockpit workload at this time included descent and approach checklists. As the aircraft was descending through approximately 11000 ft, I noticed that 1) the altitude 'arm' window in the flight mode annunciator was blank (it should have annunciated 'altitude') and that 2) the descent rate remained high. I disconnected the autoplt and leveled off the aircraft. The aircraft descended to approximately 9600 ft MSL before climbing back to 10000 ft (assigned). No traffic conflicts were reported by ATC or TCASII. Flight landed at sna with no further incident. I take full responsibility for this altitude deviation, but I believe that a contributing factor was the fact that the 'arm' window of the flight mode annunciator (FMA) blanked out most probably when changing from 'VNAV' to 'IAS' on the flight guidance panel. This canceled the automatic level off at 10000 ft. This anomaly is peculiar to the MD88/MD90 autoflt system.

Original NASA ASRS Text

Title: MD88 OVERSHOT 10000 FT IN DSCNT.

Narrative: WE WERE CLRED TO DSND FROM FL240 TO 10000 FT ON THE EASTSIDE 1 ARR INTO SNA. DSCNT WAS INITIATED IN THE 'VNAV' MODE OF AUTOFLT AND CHANGED TO 'IAS' DURING THE DSCNT. AS I RECALL, THIS WAS DONE AROUND 15000 FT MSL. COCKPIT WORKLOAD AT THIS TIME INCLUDED DSCNT AND APCH CHKLISTS. AS THE ACFT WAS DSNDING THROUGH APPROX 11000 FT, I NOTICED THAT 1) THE ALT 'ARM' WINDOW IN THE FLT MODE ANNUNCIATOR WAS BLANK (IT SHOULD HAVE ANNUNCIATED 'ALT') AND THAT 2) THE DSCNT RATE REMAINED HIGH. I DISCONNECTED THE AUTOPLT AND LEVELED OFF THE ACFT. THE ACFT DSNDED TO APPROX 9600 FT MSL BEFORE CLBING BACK TO 10000 FT (ASSIGNED). NO TFC CONFLICTS WERE RPTED BY ATC OR TCASII. FLT LANDED AT SNA WITH NO FURTHER INCIDENT. I TAKE FULL RESPONSIBILITY FOR THIS ALTDEV, BUT I BELIEVE THAT A CONTRIBUTING FACTOR WAS THE FACT THAT THE 'ARM' WINDOW OF THE FLT MODE ANNUNCIATOR (FMA) BLANKED OUT MOST PROBABLY WHEN CHANGING FROM 'VNAV' TO 'IAS' ON THE FLT GUIDANCE PANEL. THIS CANCELED THE AUTO LEVEL OFF AT 10000 FT. THIS ANOMALY IS PECULIAR TO THE MD88/MD90 AUTOFLT SYS.

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.