A hawker 125-800XP on leveloff at 15000 ft with autoplt engaged made a sudden 400 ft pitch up.

Attributes
ACN	431764
Time
Date	199903
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : n90.tracon
State Reference	NY
Altitude	msl bound lower : 15000 msl bound upper : 15400
Environment
Light	Daylight
Person 1
Affiliation	company : corporate
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 90 flight time total : 18000 flight time type : 2000
ASRS Report	431764
Person 2
Affiliation	company : corporate
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial pilot : multi engine
Events
Anomaly	aircraft equipment problem : critical altitude deviation : overshoot maintenance problem : improper maintenance other anomaly
Independent Detector	aircraft equipment other aircraft equipment : altimeter other flight crewa
Resolutory Action	flight crew : regained aircraft control flight crew : returned to assigned airspace
Consequence	other
Factors
Maintenance	contributing factor : engineering procedure performance deficiency : fault isolation performance deficiency : repair
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

On climb out of hpn and being radar vectored, we were climbing to 1500 ft MSL in vertical mode and the autoplt captured the altitude and started to level off but then pitched up hard. By the time I disconnected, I was at 15400 ft MSL. Flew the aircraft back to 15000 ft MSL, checked trim and re-engaged autoplt. Worked good for the rest of trip. Maintenance was told and aircraft was scheduled in for maintenance. Callback conversation with reporter revealed the following information: the reporter stated the aircraft was a hawker 125-800XP with an aps-85 built by honeywell. The reporter said this autoplt system has a fleet wide problem of uncommanded mode switching. The reporter said the aircraft was removed from service but the reporter was not advised of the maintenance action taken.

Original NASA ASRS Text

Title: A HAWKER 125-800XP ON LEVELOFF AT 15000 FT WITH AUTOPLT ENGAGED MADE A SUDDEN 400 FT PITCH UP.

Narrative: ON CLBOUT OF HPN AND BEING RADAR VECTORED, WE WERE CLBING TO 1500 FT MSL IN VERT MODE AND THE AUTOPLT CAPTURED THE ALT AND STARTED TO LEVEL OFF BUT THEN PITCHED UP HARD. BY THE TIME I DISCONNECTED, I WAS AT 15400 FT MSL. FLEW THE ACFT BACK TO 15000 FT MSL, CHKED TRIM AND RE-ENGAGED AUTOPLT. WORKED GOOD FOR THE REST OF TRIP. MAINT WAS TOLD AND ACFT WAS SCHEDULED IN FOR MAINT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE ACFT WAS A HAWKER 125-800XP WITH AN APS-85 BUILT BY HONEYWELL. THE RPTR SAID THIS AUTOPLT SYS HAS A FLEET WIDE PROB OF UNCOMMANDED MODE SWITCHING. THE RPTR SAID THE ACFT WAS REMOVED FROM SVC BUT THE RPTR WAS NOT ADVISED OF THE MAINT ACTION TAKEN.

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.