First officer of a DC9 overshot descent altitude causing TCASII RA with another aircraft level 1000 ft below his flight level due to the autoplt failing to level the aircraft at the preselected altitude.

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Attributes
ACN	465760
Time
Date	200003
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	navaid : dqn.vortac
State Reference	OH
Altitude	msl bound lower : 28900 msl bound upper : 29000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zob.artcc
Operator	common carrier : air carrier
Make Model Name	DC-9 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	other vortac
Flight Phase	cruise : enroute altitude change
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zob.artcc
Make Model Name	Commercial Fixed Wing
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 130 flight time total : 10000 flight time type : 2800
ASRS Report	465760
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : critical altitude deviation : overshoot non adherence : clearance
Independent Detector	aircraft equipment : tcas other flight crewa
Resolutory Action	flight crew : returned to assigned altitude flight crew : took precautionary avoidance action
Consequence	Other
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft
Primary Problem	Flight Crew Human Performance

Narrative:

During a descent from FL330 to FL290, ATC requested a descent rate of 2000 FPM or greater for traffic. As I reduced our descent rate for leveloff at FL290 and gave a level flight command at FL291, ATC notified us regarding traffic at FL280. In the cockpit we verified the autoplt command and leveloff for FL290. However, the vsi was indicating a 100-200 FPM rate of descent. To stop the descent I gave a climb command to the autoplt. Instead of showing a climb, the vsi indicated a descent rate of 200 FPM and increasing. At this time our altitude indicated FL289, I disconnected the autoplt and initiated a climb to leveloff at FL290. We received a TCASII RA followed by 'climb and clear conflict.' the lowest altitude noted during this advisory was FL289 on my altimeter. In the DC9's, crew should avoid accepting high descent rates. Rates greater than 1000 FPM within 1500 ft of assigned altitude should be closely monitored.

Original NASA ASRS Text

Title: FO OF A DC9 OVERSHOT DSCNT ALT CAUSING TCASII RA WITH ANOTHER ACFT LEVEL 1000 FT BELOW HIS FLT LEVEL DUE TO THE AUTOPLT FAILING TO LEVEL THE ACFT AT THE PRESELECTED ALT.

Narrative: DURING A DSCNT FROM FL330 TO FL290, ATC REQUESTED A DSCNT RATE OF 2000 FPM OR GREATER FOR TFC. AS I REDUCED OUR DSCNT RATE FOR LEVELOFF AT FL290 AND GAVE A LEVEL FLT COMMAND AT FL291, ATC NOTIFIED US REGARDING TFC AT FL280. IN THE COCKPIT WE VERIFIED THE AUTOPLT COMMAND AND LEVELOFF FOR FL290. HOWEVER, THE VSI WAS INDICATING A 100-200 FPM RATE OF DSCNT. TO STOP THE DSCNT I GAVE A CLB COMMAND TO THE AUTOPLT. INSTEAD OF SHOWING A CLB, THE VSI INDICATED A DSCNT RATE OF 200 FPM AND INCREASING. AT THIS TIME OUR ALT INDICATED FL289, I DISCONNECTED THE AUTOPLT AND INITIATED A CLB TO LEVELOFF AT FL290. WE RECEIVED A TCASII RA FOLLOWED BY 'CLB AND CLR CONFLICT.' THE LOWEST ALT NOTED DURING THIS ADVISORY WAS FL289 ON MY ALTIMETER. IN THE DC9'S, CREW SHOULD AVOID ACCEPTING HIGH DSCNT RATES. RATES GREATER THAN 1000 FPM WITHIN 1500 FT OF ASSIGNED ALT SHOULD BE CLOSELY MONITORED.

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.