An air carrier first officer complains that the autoplt did not level the aircraft as commanded.

Attributes
ACN	263943
Time
Date	199402
Day	Mon
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : rmg
State Reference	GA
Altitude	msl bound lower : 23400 msl bound upper : 24000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : ztl tower : fmn
Operator	common carrier : air carrier
Make Model Name	MD-88
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : flight engineer pilot : instrument pilot : private pilot : commercial pilot : atp
Experience	flight time last 90 days : 150 flight time total : 3800 flight time type : 2300
ASRS Report	263943
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 non adherence : clearance
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : overcame equipment problem flight crew : became reoriented
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

Problem arose when the autoplt didn't level off at FL240. It was discovered when the 'altitude' warning sounded passing FL236. Switched to manual control and returned aircraft to FL240. Lowest altitude was FL234. Contributing factors were: 1) vectored off course for spacing on arrival, and after FMA displayed 'altitude cap,' I diverted my attention to constructing a new descent profile into FMS. 2) descent airspeed was 320 KTS, level off airspeed for cruise at FL240 was 250 KTS. During slow-down, the autoplt trim could not keep up, so aircraft could not hold altitude. When switched to manual, I noticed a lot of nose down trim. Human performance considerations: it is very easy to put too much confidence in aircraft automation resulting in lack of proper monitoring during events such as level-offs and course intercepts. It is important to always find the proper balance for using/not using automation and programming it. We have noticed in some md-88's that the autoplt trim has trouble keeping up with airspeed and confign changes, and I believe this is the primary reason for the aircraft not leveling off at FL240 with the autoplt on. This should have been prevented with better monitoring of the level off and ensuring the aircraft was stable at FL240 before diverting attention to other duties.

Original NASA ASRS Text

Title: AN ACR FO COMPLAINS THAT THE AUTOPLT DID NOT LEVEL THE ACFT AS COMMANDED.

Narrative: PROB AROSE WHEN THE AUTOPLT DIDN'T LEVEL OFF AT FL240. IT WAS DISCOVERED WHEN THE 'ALT' WARNING SOUNDED PASSING FL236. SWITCHED TO MANUAL CTL AND RETURNED ACFT TO FL240. LOWEST ALT WAS FL234. CONTRIBUTING FACTORS WERE: 1) VECTORED OFF COURSE FOR SPACING ON ARR, AND AFTER FMA DISPLAYED 'ALT CAP,' I DIVERTED MY ATTN TO CONSTRUCTING A NEW DSCNT PROFILE INTO FMS. 2) DSCNT AIRSPD WAS 320 KTS, LEVEL OFF AIRSPD FOR CRUISE AT FL240 WAS 250 KTS. DURING SLOW-DOWN, THE AUTOPLT TRIM COULD NOT KEEP UP, SO ACFT COULD NOT HOLD ALT. WHEN SWITCHED TO MANUAL, I NOTICED A LOT OF NOSE DOWN TRIM. HUMAN PERFORMANCE CONSIDERATIONS: IT IS VERY EASY TO PUT TOO MUCH CONFIDENCE IN ACFT AUTOMATION RESULTING IN LACK OF PROPER MONITORING DURING EVENTS SUCH AS LEVEL-OFFS AND COURSE INTERCEPTS. IT IS IMPORTANT TO ALWAYS FIND THE PROPER BAL FOR USING/NOT USING AUTOMATION AND PROGRAMMING IT. WE HAVE NOTICED IN SOME MD-88'S THAT THE AUTOPLT TRIM HAS TROUBLE KEEPING UP WITH AIRSPD AND CONFIGN CHANGES, AND I BELIEVE THIS IS THE PRIMARY REASON FOR THE ACFT NOT LEVELING OFF AT FL240 WITH THE AUTOPLT ON. THIS SHOULD HAVE BEEN PREVENTED WITH BETTER MONITORING OF THE LEVEL OFF AND ENSURING THE ACFT WAS STABLE AT FL240 BEFORE DIVERTING ATTN TO OTHER DUTIES.

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.