Altitude excursion.

Attributes
ACN	293214
Time
Date	199501
Day	Mon
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : esf
State Reference	LA
Altitude	msl bound lower : 41000 msl bound upper : 41300
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Controlling Facilities	artcc : zme artcc : zjx
Operator	common carrier : air taxi
Make Model Name	Learjet 25
Operating Under FAR Part	Part 135
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air taxi
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 180 flight time total : 7400 flight time type : 80
ASRS Report	293314
Person 2
Affiliation	company : air taxi
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude other anomaly other
Independent Detector	other controllera other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course flight crew : regained aircraft control flight crew : overcame equipment problem
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation other

Narrative:

This was the second revenue day for this particular lear 25 since put on the certificate. Aircraft was in cruise at FL410, autoplt engaged, altitude hold, heading engaged. Aircraft was level, autoplt suddenly deviated in altitude. PF attempted to correct altitude with manual pitch wheel. Pitch was difficult to control in pitch mode. This happened a couple of times maximum altitude deviation was approximately 300 ft. No conflict reported by ATC other than stating altitude shows 300 ft high at 1 point. Also circuit breaker popped on flight director computer. At this time it's unknown whether this contributed to the problem. Aircraft was written up for erratic autoplt operation and circuit breaker popped. Increased vigilance prevented from further deviations.

Original NASA ASRS Text

Title: ALT EXCURSION.

Narrative: THIS WAS THE SECOND REVENUE DAY FOR THIS PARTICULAR LEAR 25 SINCE PUT ON THE CERTIFICATE. ACFT WAS IN CRUISE AT FL410, AUTOPLT ENGAGED, ALT HOLD, HDG ENGAGED. ACFT WAS LEVEL, AUTOPLT SUDDENLY DEVIATED IN ALT. PF ATTEMPTED TO CORRECT ALT WITH MANUAL PITCH WHEEL. PITCH WAS DIFFICULT TO CTL IN PITCH MODE. THIS HAPPENED A COUPLE OF TIMES MAX ALTDEV WAS APPROX 300 FT. NO CONFLICT RPTED BY ATC OTHER THAN STATING ALT SHOWS 300 FT HIGH AT 1 POINT. ALSO CIRCUIT BREAKER POPPED ON FLT DIRECTOR COMPUTER. AT THIS TIME IT'S UNKNOWN WHETHER THIS CONTRIBUTED TO THE PROB. ACFT WAS WRITTEN UP FOR ERRATIC AUTOPLT OP AND CIRCUIT BREAKER POPPED. INCREASED VIGILANCE PREVENTED FROM FURTHER DEVS.

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.