An MD80 captain flying at 2000 ft 4 mi final approach on GS noted aircraft too low. First officer's ...

Attributes
ACN	638510
Time
Date	200411
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : aus.airport
State Reference	TX
Altitude	msl bound lower : 1800 msl bound upper : 2000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : aus.tracon
Operator	common carrier : air carrier
Make Model Name	MD-83
Operating Under FAR Part	Part 121
Navigation In Use	ils localizer & glide slope : 17r other
Flight Phase	descent : approach
Route In Use	approach : visual
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
ASRS Report	638510
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
ASRS Report	638509
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	aircraft equipment other aircraft equipment : left glide slope out of lights other flight crewa other flight crewb
Resolutory Action	none taken : detected after the fact
Consequence	other other
Supplementary
Problem Areas	Company Chart Or Publication Aircraft Flight Crew Human Performance
Primary Problem	Aircraft

Narrative:

During the approach to runway 17R in aus with the ILS tuned and idented, we noticed that my GS indication was showing right on glide path while the first officer's was 1 DOT low. We were visual at the time and at approximately 4 mi out on final. I thought that I was too low to be this far out and checked the first officer's side. We then re-tuned the ILS and also tried switching the 'rad navigation' switch. I attempted to try manual ILS by turning off the FMS. Nothing worked and the ILS continued to show false on glide path information with no warning or comparator lights. This is a former air carrier Y bird that has been modified. We might want to check and see if the wiring has a problem with this jet and others like it. This could be a potential problem and cause numerous missed approachs due to erroneous information with no warning flaps. A good xchk should catch it, but we should try and correct this quickly. Callback conversation with reporter revealed the following information: the reporter said, 'my GS indicator was centered, but looking outside the airplane it appeared too low on profile.' the first officer agreed and stated the right GS indicator was 1 DOT low while the captain's indicator displayed exactly on GS. There was no warning flag or comparator alert. All other system operated normally. The reporter stated this airplane was a buyout airplane and has been modified to somewhat like the acquiring carrier's fleet. This difference is of great concern and is a potential problem. Maintenance cleared the report with removed and replaced. No other details. Callback conversation with reporter acn 638509 revealed the following information: the reporter state that on final approach the captain remarked that he seemed low on profile and he was right 1 DOT low on the right GS indicator. All navaids were properly tuned and both system on correct frequency. No warning of any kind alerted this difference. The logbook was cleared as re-racked units.

Original NASA ASRS Text

Title: AN MD80 CAPT FLYING AT 2000 FT 4 MI FINAL APCH ON GS NOTED ACFT TOO LOW. FO'S GS INDICATOR 1 DOT LOW. NO WARNING FLAGS OR COMPARATOR ALERT.

Narrative: DURING THE APCH TO RWY 17R IN AUS WITH THE ILS TUNED AND IDENTED, WE NOTICED THAT MY GS INDICATION WAS SHOWING R ON GLIDE PATH WHILE THE FO'S WAS 1 DOT LOW. WE WERE VISUAL AT THE TIME AND AT APPROX 4 MI OUT ON FINAL. I THOUGHT THAT I WAS TOO LOW TO BE THIS FAR OUT AND CHKED THE FO'S SIDE. WE THEN RE-TUNED THE ILS AND ALSO TRIED SWITCHING THE 'RAD NAV' SWITCH. I ATTEMPTED TO TRY MANUAL ILS BY TURNING OFF THE FMS. NOTHING WORKED AND THE ILS CONTINUED TO SHOW FALSE ON GLIDE PATH INFO WITH NO WARNING OR COMPARATOR LIGHTS. THIS IS A FORMER ACR Y BIRD THAT HAS BEEN MODIFIED. WE MIGHT WANT TO CHK AND SEE IF THE WIRING HAS A PROB WITH THIS JET AND OTHERS LIKE IT. THIS COULD BE A POTENTIAL PROB AND CAUSE NUMEROUS MISSED APCHS DUE TO ERRONEOUS INFO WITH NO WARNING FLAPS. A GOOD XCHK SHOULD CATCH IT, BUT WE SHOULD TRY AND CORRECT THIS QUICKLY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR SAID, 'MY GS INDICATOR WAS CTRED, BUT LOOKING OUTSIDE THE AIRPLANE IT APPEARED TOO LOW ON PROFILE.' THE FO AGREED AND STATED THE R GS INDICATOR WAS 1 DOT LOW WHILE THE CAPT'S INDICATOR DISPLAYED EXACTLY ON GS. THERE WAS NO WARNING FLAG OR COMPARATOR ALERT. ALL OTHER SYS OPERATED NORMALLY. THE RPTR STATED THIS AIRPLANE WAS A BUYOUT AIRPLANE AND HAS BEEN MODIFIED TO SOMEWHAT LIKE THE ACQUIRING CARRIER'S FLEET. THIS DIFFERENCE IS OF GREAT CONCERN AND IS A POTENTIAL PROB. MAINT CLRED THE RPT WITH REMOVED AND REPLACED. NO OTHER DETAILS. CALLBACK CONVERSATION WITH RPTR ACN 638509 REVEALED THE FOLLOWING INFO: THE RPTR STATE THAT ON FINAL APCH THE CAPT REMARKED THAT HE SEEMED LOW ON PROFILE AND HE WAS R 1 DOT LOW ON THE R GS INDICATOR. ALL NAVAIDS WERE PROPERLY TUNED AND BOTH SYS ON CORRECT FREQ. NO WARNING OF ANY KIND ALERTED THIS DIFFERENCE. THE LOGBOOK WAS CLRED AS RE-RACKED UNITS.

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.

An MD80 captain flying at 2000 ft 4 mi final approach on GS noted aircraft too low. First officer's GS indicator 1 DOT low. No warning flags or comparator alert.