Heading deviation during radar vector for ILS approach. Inoperative compass system #2.

Attributes
ACN	117723
Time
Date	198907
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : msp
State Reference	MN
Altitude	msl bound lower : 4000 msl bound upper : 4000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : msp tower : abq
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other cruise other descent : approach
Route In Use	arrival other enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : cfi pilot : atp
Experience	flight time last 90 days : 225 flight time total : 8200 flight time type : 2700
ASRS Report	117723
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : critical non adherence : clearance other anomaly other other spatial deviation
Independent Detector	other controllera other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course flight crew : overcame equipment problem none taken : unable
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

During the initial approach vectoring the first officer called an error between the #1 and #2 compass systems. The aircraft was level and it was determined the #2 first officer's compass was in error. The #2 compass drives the captain's HSI, the primary instrument for heading and navigation on the localizer. I requested the first officer to pull and reset his slaving knob. Both compass systems appeared to be operating satisfactorily and no flags were showing. ATC instructed us to fly the intercept heading of 090 degrees and cleared for the ILS 11R approach. The flight was in and out of a heavy broken layer of clouds and light rain. At some point after initiating the turn it became apparent an error was still present in the compass systems. The #2 compass and my HSI indicated less than 090 degrees, the #1 indicated 180 degrees, no flags on either system. I leveled the aircraft to check the whiskey compass as the approach controller requested our heading. We informed ATC of our compass problem and began a left turn. I completed the approach using the #1 compass and the first officer's HSI. The compass problem was entered in aircraft log book after block in.

Original NASA ASRS Text

Title: HEADING DEVIATION DURING RADAR VECTOR FOR ILS APCH. INOPERATIVE COMPASS SYSTEM #2.

Narrative: DURING THE INITIAL APCH VECTORING THE F/O CALLED AN ERROR BTWN THE #1 AND #2 COMPASS SYSTEMS. THE ACFT WAS LEVEL AND IT WAS DETERMINED THE #2 F/O'S COMPASS WAS IN ERROR. THE #2 COMPASS DRIVES THE CAPT'S HSI, THE PRIMARY INSTRUMENT FOR HDG AND NAV ON THE LOC. I REQUESTED THE F/O TO PULL AND RESET HIS SLAVING KNOB. BOTH COMPASS SYSTEMS APPEARED TO BE OPERATING SATISFACTORILY AND NO FLAGS WERE SHOWING. ATC INSTRUCTED US TO FLY THE INTERCEPT HDG OF 090 DEGS AND CLRED FOR THE ILS 11R APCH. THE FLT WAS IN AND OUT OF A HVY BROKEN LAYER OF CLOUDS AND LIGHT RAIN. AT SOME POINT AFTER INITIATING THE TURN IT BECAME APPARENT AN ERROR WAS STILL PRESENT IN THE COMPASS SYSTEMS. THE #2 COMPASS AND MY HSI INDICATED LESS THAN 090 DEGS, THE #1 INDICATED 180 DEGS, NO FLAGS ON EITHER SYS. I LEVELED THE ACFT TO CHK THE WHISKEY COMPASS AS THE APCH CTLR REQUESTED OUR HDG. WE INFORMED ATC OF OUR COMPASS PROB AND BEGAN A LEFT TURN. I COMPLETED THE APCH USING THE #1 COMPASS AND THE F/O'S HSI. THE COMPASS PROB WAS ENTERED IN ACFT LOG BOOK AFTER BLOCK IN.

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.