Corporate light transport in cruise at FL330 experiences uncommanded pitch down while on autoplt.

Attributes
ACN	134789
Time
Date	199001
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : ink
State Reference	TX
Altitude	msl bound lower : 32600 msl bound upper : 33400
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zfw artcc : zau
Operator	general aviation : corporate
Make Model Name	Light Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 50 flight time total : 9200 flight time type : 450
ASRS Report	134789
Person 2
Affiliation	Other
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly
Independent Detector	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

Narrative:

Level at FL330, center issued vector turn. Was on autoplt and flight director. Turn initiated by heading bug. Aircraft made sudden unexpected nose down. Lost about 300-400' and correction resulted in 300-400' plus altitude deviation. With pilot in manual control, it was noticed that the flight director was commanding nose down when it should have been commanding nose up and vice versa. Remainder of flight completed west/O flight director on ground discovered static line to flight director altitude computer box was loose. Retightening this static connection solved the problem.

Original NASA ASRS Text

Title: CORPORATE LTT IN CRUISE AT FL330 EXPERIENCES UNCOMMANDED PITCH DOWN WHILE ON AUTOPLT.

Narrative: LEVEL AT FL330, CENTER ISSUED VECTOR TURN. WAS ON AUTOPLT AND FLT DIRECTOR. TURN INITIATED BY HDG BUG. ACFT MADE SUDDEN UNEXPECTED NOSE DOWN. LOST ABOUT 300-400' AND CORRECTION RESULTED IN 300-400' PLUS ALT DEVIATION. WITH PLT IN MANUAL CTL, IT WAS NOTICED THAT THE FLT DIRECTOR WAS COMMANDING NOSE DOWN WHEN IT SHOULD HAVE BEEN COMMANDING NOSE UP AND VICE VERSA. REMAINDER OF FLT COMPLETED W/O FLT DIRECTOR ON GND DISCOVERED STATIC LINE TO FLT DIRECTOR ALT COMPUTER BOX WAS LOOSE. RETIGHTENING THIS STATIC CONNECTION SOLVED THE PROB.

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.