A B757-200 autoplt fails to capture its assigned altitude 10 mi northeast of las, nv.

Attributes
ACN	483102
Time
Date	200008
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	navaid : las.vortac
Altitude	msl bound lower : 15000 msl bound upper : 15400
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Navigation In Use	other other vortac
Flight Phase	climbout : intermediate altitude
Route In Use	departure : on vectors departure sid : oveto
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 210 flight time total : 18000 flight time type : 5000
ASRS Report	483102
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : instrument pilot : commercial
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : overshoot cabin event : passenger electronic device cabin event : passenger misconduct non adherence : far non adherence : clearance other anomaly other anomaly other
Independent Detector	other flight crewa
Resolutory Action	aircraft : equipment problem dissipated flight crew : regained aircraft control flight crew : returned to intended or assigned course flight crew : returned to assigned altitude
Consequence	Other
Supplementary
Problem Areas	Aircraft Passenger Human Performance Flight Crew Human Performance
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

Aircraft climbing to 15000 ft on VNAV, LNAV selected and armed while on heading select. Aircraft intercepted 050 degree radial on oveto departure. LNAV captured but continued to turn through radial. Selected heading and redirected aircraft to radial. Again, LNAV failed to capture. Approaching 15000 ft and tracking radial on heading select, center autoplt engaged. At leveloff, aircraft pitched up rather sharply. Disengaged autoplt, retarded throttles to idle, and pushed nose over with authority/authorized and concern for passenger and flight attendants. Stopped the uncommanded climb at approximately 15400 ft and immediately leveled the aircraft at 15000 ft. Excursion probably lasted 20-30 seconds at most, with no conflicting traffic on TCASII. (During this time, first officer was in the process of switching frequencys from las departure to ZLA.) re-engaged autoplt using right autoplt and LNAV. I've flown the B757 for over 10 yrs and never have seen the likes of this before. At the time of the problem, the aircraft acted as if it were under the influence of some electronic glitch or outside influence. All-in-all, very puzzling. Later in the flight, tried center autoplt in order to glean information for maintenance write-up and had no problems at all!

Original NASA ASRS Text

Title: A B757-200 AUTOPLT FAILS TO CAPTURE ITS ASSIGNED ALT 10 MI NE OF LAS, NV.

Narrative: ACFT CLBING TO 15000 FT ON VNAV, LNAV SELECTED AND ARMED WHILE ON HDG SELECT. ACFT INTERCEPTED 050 DEG RADIAL ON OVETO DEP. LNAV CAPTURED BUT CONTINUED TO TURN THROUGH RADIAL. SELECTED HDG AND REDIRECTED ACFT TO RADIAL. AGAIN, LNAV FAILED TO CAPTURE. APCHING 15000 FT AND TRACKING RADIAL ON HDG SELECT, CTR AUTOPLT ENGAGED. AT LEVELOFF, ACFT PITCHED UP RATHER SHARPLY. DISENGAGED AUTOPLT, RETARDED THROTTLES TO IDLE, AND PUSHED NOSE OVER WITH AUTH AND CONCERN FOR PAX AND FLT ATTENDANTS. STOPPED THE UNCOMMANDED CLB AT APPROX 15400 FT AND IMMEDIATELY LEVELED THE ACFT AT 15000 FT. EXCURSION PROBABLY LASTED 20-30 SECONDS AT MOST, WITH NO CONFLICTING TFC ON TCASII. (DURING THIS TIME, FO WAS IN THE PROCESS OF SWITCHING FREQS FROM LAS DEP TO ZLA.) RE-ENGAGED AUTOPLT USING R AUTOPLT AND LNAV. I'VE FLOWN THE B757 FOR OVER 10 YRS AND NEVER HAVE SEEN THE LIKES OF THIS BEFORE. AT THE TIME OF THE PROB, THE ACFT ACTED AS IF IT WERE UNDER THE INFLUENCE OF SOME ELECTRONIC GLITCH OR OUTSIDE INFLUENCE. ALL-IN-ALL, VERY PUZZLING. LATER IN THE FLT, TRIED CTR AUTOPLT IN ORDER TO GLEAN INFO FOR MAINT WRITE-UP AND HAD NO PROBS AT ALL!

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.