HSI failure on descent and approach to landing.

Attributes
ACN	125911
Time
Date	198910
Day	Sun
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : ord
State Reference	IL
Altitude	msl bound lower : 5000 msl bound upper : 6000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : ord
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent : approach landing other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : cfi pilot : flight engineer pilot : instrument pilot : atp
Experience	flight time last 90 days : 100 flight time total : 5000 flight time type : 580
ASRS Report	125911
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : instrument pilot : flight engineer pilot : atp pilot : cfi pilot : commercial
Experience	flight time last 90 days : 210 flight time total : 11000 flight time type : 2000
ASRS Report	125792
Events
Anomaly	aircraft equipment problem : critical other spatial deviation
Independent Detector	other controllera other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course none taken : unable other
Consequence	Other Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

The HSI and rmdi gave incorrect readings during our approach to ILS into ord. We checked them (pre-checklist) out of 10000', and they checked ok. When we received vectors from approach, the incorrect reading on our instruments, caused our course to differ substantially from what ATC wanted. Maintenance found our computer experienced 3 different types of malfunctions, all of which we believed to occur low level at this critical time to approach. We were issued visibility landing clearance.

Original NASA ASRS Text

Title: HSI FAILURE ON DESCENT AND APCH TO LNDG.

Narrative: THE HSI AND RMDI GAVE INCORRECT READINGS DURING OUR APCH TO ILS INTO ORD. WE CHKED THEM (PRE-CHKLIST) OUT OF 10000', AND THEY CHKED OK. WHEN WE RECEIVED VECTORS FROM APCH, THE INCORRECT READING ON OUR INSTRUMENTS, CAUSED OUR COURSE TO DIFFER SUBSTANTIALLY FROM WHAT ATC WANTED. MAINT FOUND OUR COMPUTER EXPERIENCED 3 DIFFERENT TYPES OF MALFUNCTIONS, ALL OF WHICH WE BELIEVED TO OCCUR LOW LEVEL AT THIS CRITICAL TIME TO APCH. WE WERE ISSUED VIS LNDG CLRNC.

Data retrieved from NASA's ASRS site as of August 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.