DC10 flight crew experiences uncommanded pitch oscillations.

Attributes
ACN	440554
Time
Date	199906
Day	Sun
Local Time Of Day	0001 To 0600
Place
Locale Reference	navaid : cim.vortac
State Reference	NM
Altitude	msl bound lower : 30600 msl bound upper : 31000
Environment
Light	Night
Aircraft 1
Controlling Facilities	artcc : zab.artcc tower : dfw.tower
Operator	common carrier : air carrier
Make Model Name	DC-10 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : commercial pilot : instrument
ASRS Report	440553
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	440554
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other flight crewa other flight crewb other other : 3
Resolutory Action	flight crew : overcame equipment problem flight crew : returned to assigned altitude
Consequence	other
Supplementary
Problem Areas	Aircraft Flight Crew Human Performance Weather
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

Cruising at FL310 in the vicinity of cim VORTAC, autoplt #1 engaged. Experienced uncommanded pitch oscillations -- primarily in the down direction. Appeared, at first, to be mountain wave activity. Achieved 1000 FPM down on vsi's before captain (PF) could disconnect autoplt and return aircraft to level flight. Lost approximately 400 ft. Informed ZAB of altitude loss due to mountain wave and returned aircraft to FL310. No terrain or aircraft conflicts apparent. Further analysis revealed oscillating pitch bar in captain's vdi. We concluded the loss was not mountain wave, but a flight director/autoplt pitch malfunction. Used autoplt #2 for remainder of flight without further problems.

Original NASA ASRS Text

Title: DC10 FLC EXPERIENCES UNCOMMANDED PITCH OSCILLATIONS.

Narrative: CRUISING AT FL310 IN THE VICINITY OF CIM VORTAC, AUTOPLT #1 ENGAGED. EXPERIENCED UNCOMMANDED PITCH OSCILLATIONS -- PRIMARILY IN THE DOWN DIRECTION. APPEARED, AT FIRST, TO BE MOUNTAIN WAVE ACTIVITY. ACHIEVED 1000 FPM DOWN ON VSI'S BEFORE CAPT (PF) COULD DISCONNECT AUTOPLT AND RETURN ACFT TO LEVEL FLT. LOST APPROX 400 FT. INFORMED ZAB OF ALT LOSS DUE TO MOUNTAIN WAVE AND RETURNED ACFT TO FL310. NO TERRAIN OR ACFT CONFLICTS APPARENT. FURTHER ANALYSIS REVEALED OSCILLATING PITCH BAR IN CAPT'S VDI. WE CONCLUDED THE LOSS WAS NOT MOUNTAIN WAVE, BUT A FLT DIRECTOR/AUTOPLT PITCH MALFUNCTION. USED AUTOPLT #2 FOR REMAINDER OF FLT WITHOUT FURTHER PROBS.

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.