Altitude deviation.

Attributes
ACN	279909
Time
Date	199408
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : mbs
State Reference	MI
Altitude	msl bound lower : 11700 msl bound upper : 12000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : bwi
Operator	common carrier : air carrier
Make Model Name	A320
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent other
Route In Use	arrival star : star enroute airway : zob
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument pilot : atp
Experience	flight time last 90 days : 180 flight time total : 8000 flight time type : 700
ASRS Report	279909
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : overshoot altitude deviation : crossing restriction not met non adherence : clearance
Independent Detector	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	other

Narrative:

On our descent to dtw on the polar 1 STAR, we were cleared to cross polar at 12000 ft and 250 KTS. I programmed the FMGC VNAV on the airbus A320 to meet the restr. During descent, my screens flashed off for a second and displayed single horizontal lines across them like they would with a dual master computer failure but then returned to normal. The airplane failed to capture 12000 ft and I turned the autoplt off at 11800 ft and manually flew the airplane back up to 12000 ft. I believe our lowest altitude was 11700 ft: we wrote up the problem for dtw maintenance to look at.

Original NASA ASRS Text

Title: ALTDEV.

Narrative: ON OUR DSCNT TO DTW ON THE POLAR 1 STAR, WE WERE CLRED TO CROSS POLAR AT 12000 FT AND 250 KTS. I PROGRAMMED THE FMGC VNAV ON THE AIRBUS A320 TO MEET THE RESTR. DURING DSCNT, MY SCREENS FLASHED OFF FOR A SECOND AND DISPLAYED SINGLE HORIZ LINES ACROSS THEM LIKE THEY WOULD WITH A DUAL MASTER COMPUTER FAILURE BUT THEN RETURNED TO NORMAL. THE AIRPLANE FAILED TO CAPTURE 12000 FT AND I TURNED THE AUTOPLT OFF AT 11800 FT AND MANUALLY FLEW THE AIRPLANE BACK UP TO 12000 FT. I BELIEVE OUR LOWEST ALT WAS 11700 FT: WE WROTE UP THE PROB FOR DTW MAINT TO LOOK AT.

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.