B727 with flight instrument problems results in crew flying through localizer on ILS approach.

Attributes
ACN	451887
Time
Date	199910
Day	Sun
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : iah.airport
State Reference	TX
Altitude	msl single value : 2000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	B727 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	ils localizer & glide slope : 36 other
Flight Phase	descent : approach
Route In Use	approach : instrument precision
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : cfi pilot : atp
Experience	flight time last 90 days : 240 flight time total : 14000 flight time type : 1000
ASRS Report	451887
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : multi engine pilot : atp
Events
Anomaly	aircraft equipment problem : less severe non adherence : published procedure non adherence : clearance other spatial deviation
Independent Detector	other controllera
Resolutory Action	controller : issued advisory flight crew : overcame equipment problem flight crew : became reoriented
Consequence	other
Supplementary
Problem Areas	Aircraft Flight Crew Human Performance
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

On right downwind to runway 26 both captain and I switched from GPS mode to VOR/localizer on navigation selector. Approach check was run and radios tuned and idented. Approach gave me a 230 degree heading to intercept the runway 26 localizer. The localizer on the right side never had case break but the captain's localizer did. Neither of us caught it. Because we were in a broken layer the captain was looking out the window and did not notice case break on his localizer needle. I was inside on my instruments and my localizer needle did not move. Approach called and told us we had flown through the localizer. At about the same time we broke out of clouds and saw that we were almost lined up on runway 27. I began the right turn back to runway 26 and recycled VOR/localizer/GPS switch. When I did that the localizer needle showed full scale deflection to right. The captain stated that that had happened to him before. When GPS/VOR button is pushed the indication is that navigation mode has changed when in fact the mode has not switched and therefore the obs needle reads the wrong information. On my part, I should have xrefed the captain's instruments and he also should have monitored his more closely.

Original NASA ASRS Text

Title: B727 WITH FLT INST PROBS RESULTS IN CREW FLYING THROUGH LOC ON ILS APCH.

Narrative: ON R DOWNWIND TO RWY 26 BOTH CAPT AND I SWITCHED FROM GPS MODE TO VOR/LOC ON NAV SELECTOR. APCH CHK WAS RUN AND RADIOS TUNED AND IDENTED. APCH GAVE ME A 230 DEG HDG TO INTERCEPT THE RWY 26 LOC. THE LOC ON THE R SIDE NEVER HAD CASE BREAK BUT THE CAPT'S LOC DID. NEITHER OF US CAUGHT IT. BECAUSE WE WERE IN A BROKEN LAYER THE CAPT WAS LOOKING OUT THE WINDOW AND DID NOT NOTICE CASE BREAK ON HIS LOC NEEDLE. I WAS INSIDE ON MY INSTS AND MY LOC NEEDLE DID NOT MOVE. APCH CALLED AND TOLD US WE HAD FLOWN THROUGH THE LOC. AT ABOUT THE SAME TIME WE BROKE OUT OF CLOUDS AND SAW THAT WE WERE ALMOST LINED UP ON RWY 27. I BEGAN THE R TURN BACK TO RWY 26 AND RECYCLED VOR/LOC/GPS SWITCH. WHEN I DID THAT THE LOC NEEDLE SHOWED FULL SCALE DEFLECTION TO R. THE CAPT STATED THAT THAT HAD HAPPENED TO HIM BEFORE. WHEN GPS/VOR BUTTON IS PUSHED THE INDICATION IS THAT NAV MODE HAS CHANGED WHEN IN FACT THE MODE HAS NOT SWITCHED AND THEREFORE THE OBS NEEDLE READS THE WRONG INFO. ON MY PART, I SHOULD HAVE XREFED THE CAPT'S INSTS AND HE ALSO SHOULD HAVE MONITORED HIS MORE CLOSELY.

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.