Flight crew of DC9-30 descends below assigned altitude.

Attributes
ACN	407740
Time
Date	199807
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : dxo
State Reference	MI
Altitude	msl bound lower : 11800 msl bound upper : 12000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zob
Operator	common carrier : air carrier
Make Model Name	DC-9 30
Operating Under FAR Part	Part 121
Flight Phase	descent other
Route In Use	arrival other arrival star : star
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 : 10000 flight time type : 6500
ASRS Report	407740
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	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	Pilot Deviation

Narrative:

While descending into dtw on the cetus arrival, the first officer placed the descent/climb wheel on the autoplt to 'zero ft' to level the aircraft at 12000 ft. The controller had told us he was keeping us high for traffic and then would be asking for cetus at 12000 ft. The first officer was flying and because of the rate of descent we were at (2500 ft descending), I could tell the autoplt would 'bottom out' below 12000 ft. It did -- it went to 11800 ft and then back to 12000 ft. I talked to the first officer about the need to lead the altitude leveloffs more because of the tendency to bottom out with greater than 1500 FPM rate of descent.

Original NASA ASRS Text

Title: FLC OF DC9-30 DSNDS BELOW ASSIGNED ALT.

Narrative: WHILE DSNDING INTO DTW ON THE CETUS ARR, THE FO PLACED THE DSCNT/CLB WHEEL ON THE AUTOPLT TO 'ZERO FT' TO LEVEL THE ACFT AT 12000 FT. THE CTLR HAD TOLD US HE WAS KEEPING US HIGH FOR TFC AND THEN WOULD BE ASKING FOR CETUS AT 12000 FT. THE FO WAS FLYING AND BECAUSE OF THE RATE OF DSCNT WE WERE AT (2500 FT DSNDING), I COULD TELL THE AUTOPLT WOULD 'BOTTOM OUT' BELOW 12000 FT. IT DID -- IT WENT TO 11800 FT AND THEN BACK TO 12000 FT. I TALKED TO THE FO ABOUT THE NEED TO LEAD THE ALT LEVELOFFS MORE BECAUSE OF THE TENDENCY TO BOTTOM OUT WITH GREATER THAN 1500 FPM RATE OF DSCNT.

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.