Small transport has faulty flight director indication. Descends below GS.

Attributes
ACN	188647
Time
Date	199109
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : aus
State Reference	TX
Altitude	msl bound lower : 1100 msl bound upper : 2100
Aircraft 1
Controlling Facilities	tracon : aus tower : ojc
Operator	general aviation : personal
Make Model Name	Small Transport, Low Wing, 2 Turboprop Eng
Flight Phase	descent : approach
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : instrument pilot : private
Experience	flight time last 90 days : 60 flight time total : 1750 flight time type : 300
ASRS Report	188647
Person 2
Affiliation	government : faa
Function	controller : local
Qualification	controller : non radar
Events
Anomaly	aircraft equipment problem : critical non adherence : clearance other spatial deviation
Independent Detector	other controllera other other : unspecified cockpit
Resolutory Action	flight crew : returned to intended course or assigned course other
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

Assigned heading to intercept 31L localizer; maintain 2100 until established on the localizer. Clearance was issued approximately 15 mi outside the OM. Transitioned to flight director. When established on localizer, FD bars commanded down pitch. Pilot followed FD bars, descending to altitude of approximately 1100 ft GS indicator in HSI pegged at top, indicating GS above aircraft tower also advised pilot he was below GS. Corrective action taken promptly. Cause of instrument error still unknown. Unable to recommend corrective action until cause is determined.

Original NASA ASRS Text

Title: SMT HAS FAULTY FLT DIRECTOR INDICATION. DSNDS BELOW GS.

Narrative: ASSIGNED HDG TO INTERCEPT 31L LOC; MAINTAIN 2100 UNTIL ESTABLISHED ON THE LOC. CLRNC WAS ISSUED APPROX 15 MI OUTSIDE THE OM. TRANSITIONED TO FLT DIRECTOR. WHEN ESTABLISHED ON LOC, FD BARS COMMANDED DOWN PITCH. PLT FOLLOWED FD BARS, DSNDING TO ALT OF APPROX 1100 FT GS INDICATOR IN HSI PEGGED AT TOP, INDICATING GS ABOVE ACFT TWR ALSO ADVISED PLT HE WAS BELOW GS. CORRECTIVE ACTION TAKEN PROMPTLY. CAUSE OF INST ERROR STILL UNKNOWN. UNABLE TO RECOMMEND CORRECTIVE ACTION UNTIL CAUSE IS DETERMINED.

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.