A B737-300 'B' autopilot overshot an altitude on climb out and the crew received a TCAS RA. Maintena...

Narrative:

In the climbout we were cleared to 8;000 ft. Traffic was reported at one o'clock; five miles; cl-30 at 9;000 ft. The 'B' autopilot was engaged at approximately 3;000 ft MSL; and then the level change mode was engaged. As the aircraft approached 8;000 ft MSL; I was scanning outside our aircraft for the cl-30. The first officer reported that the altitude did not capture; the level change mode dropped out; and the stab out of trim light illuminated. The first officer arrested the climb at 8;800 ft MSL and began to correct to the assigned altitude. Passing 8;600 ft MSL; ATC called 'altitude alert.' we had an accompanying RA to descend; which we were in the process of doing. This aircraft had a previous writeup for the 'B' autopilot concerning altitude deviation/capture problems of approximately 100 ft to 200 ft; to my recollection. Tests were performed and aircraft was returned to service with nineteen legs being flown prior to this event. Upon taxi in and shut down at our destination the 'B' autopilot was deferred by maintenance. As we monitored the aircraft in subsequent level offs (two times to my recollection); it continued to demonstrate the autopilot errors approaching 200 ft before correcting. At this point; the autopilot use was discontinued for the duration of the flight.

Original NASA ASRS Text

Title: A B737-300 'B' autopilot overshot an altitude on climb out and the crew received a TCAS RA. Maintenance MEL'ed the 'B' side but on subsequent flights the 'A' autopilot also failed to capture the selected altitude.

Narrative: In the climbout we were cleared to 8;000 FT. Traffic was reported at one o'clock; five miles; CL-30 at 9;000 FT. The 'B' autopilot was engaged at approximately 3;000 FT MSL; and then the Level Change mode was engaged. As the aircraft approached 8;000 FT MSL; I was scanning outside our aircraft for the CL-30. The First Officer reported that the altitude did not capture; the Level Change mode dropped out; and the Stab Out of Trim light illuminated. The First Officer arrested the climb at 8;800 FT MSL and began to correct to the assigned altitude. Passing 8;600 FT MSL; ATC called 'Altitude Alert.' We had an accompanying RA to descend; which we were in the process of doing. This aircraft had a previous writeup for the 'B' Autopilot concerning altitude deviation/capture problems of approximately 100 FT to 200 FT; to my recollection. Tests were performed and aircraft was returned to service with nineteen legs being flown prior to this event. Upon taxi in and shut down at our destination the 'B' autopilot was deferred by Maintenance. As we monitored the aircraft in subsequent level offs (two times to my recollection); it continued to demonstrate the autopilot errors approaching 200 FT before correcting. At this point; the autopilot use was discontinued for the duration of the flight.

Data retrieved from NASA's ASRS site as of April 2012 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.

Attributes
ACN	910682
Time
Date	201009
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Flight Phase	Climb
Flight Plan	IFR
Aircraft 2
Make Model Name	Challenger 300
Component
Aircraft Component	Altitude Hold/Capture
Person 1
Function	Pilot Not Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 129
Events
Anomaly	Aircraft Equipment Problem Less Severe Conflict Airborne Conflict Deviation - Altitude Overshoot Deviation - Procedural Clearance

A B737-300 'B' autopilot overshot an altitude on climb out and the crew received a TCAS RA. Maintenance MEL'ed the 'B' side but on subsequent flights the 'a' autopilot also failed to capture the selected altitude.