Autoplt and yaw damper malfunctions cause altitude deviation for MU30.

Attributes
ACN	659418
Time
Date	200505
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : hys.airport
State Reference	KS
Altitude	msl single value : 27000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zkc.artcc
Operator	general aviation : corporate
Make Model Name	MU-300 Diamond 1/1A
Operating Under FAR Part	Part 91
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : corporate
Function	flight crew : captain oversight : pic
Qualification	pilot : cfi pilot : multi engine pilot : instrument pilot : atp
Experience	flight time last 90 days : 90 flight time total : 22000 flight time type : 5000
ASRS Report	659418
Person 2
Affiliation	company : corporate
Function	flight crew : first officer
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude non adherence : clearance non adherence : far other anomaly
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to assigned altitude flight crew : regained aircraft control
Consequence	other
Supplementary
Problem Areas	Aircraft Flight Crew Human Performance
Primary Problem	Aircraft

Narrative:

While in straight and level flight in calm air; our yaw damper disengaged. This caused the autoplt to disengage and the first officer immediately started hand flying the aircraft. After about 5 mins; we re-engaged the yaw damper which seemed to work normally. When we re-engaged the autoplt; the aircraft pitched down and to the left. We immediately disengaged the autoplt and began to hand fly the aircraft again. Center advised us we were 300 ft low; although we only lost about 150 ft. We then switched xponders and center advised they did not see our mode C. After switching back to the other transponder all indications seemed normal. We will have the altimeters and autoplt checked.

Original NASA ASRS Text

Title: AUTOPLT AND YAW DAMPER MALFUNCTIONS CAUSE ALTDEV FOR MU30.

Narrative: WHILE IN STRAIGHT AND LEVEL FLT IN CALM AIR; OUR YAW DAMPER DISENGAGED. THIS CAUSED THE AUTOPLT TO DISENGAGE AND THE FO IMMEDIATELY STARTED HAND FLYING THE ACFT. AFTER ABOUT 5 MINS; WE RE-ENGAGED THE YAW DAMPER WHICH SEEMED TO WORK NORMALLY. WHEN WE RE-ENGAGED THE AUTOPLT; THE ACFT PITCHED DOWN AND TO THE L. WE IMMEDIATELY DISENGAGED THE AUTOPLT AND BEGAN TO HAND FLY THE ACFT AGAIN. CTR ADVISED US WE WERE 300 FT LOW; ALTHOUGH WE ONLY LOST ABOUT 150 FT. WE THEN SWITCHED XPONDERS AND CTR ADVISED THEY DID NOT SEE OUR MODE C. AFTER SWITCHING BACK TO THE OTHER XPONDER ALL INDICATIONS SEEMED NORMAL. WE WILL HAVE THE ALTIMETERS AND AUTOPLT CHKED.

Data retrieved from NASA's ASRS site as of January 2009 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.