First officer's GS failure during an ILS approach he was flying caused a low altitude tower alert.

Attributes
ACN	320559
Time
Date	199511
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : rdu
State Reference	NC
Altitude	agl bound lower : 400 agl bound upper : 400
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : rdu
Operator	common carrier : air taxi
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 135
Flight Phase	descent : approach
Flight Plan	IFR
Person 1
Affiliation	company : air taxi
Function	flight crew : first officer
Qualification	other other : other pilot : atp
Experience	flight time last 90 days : 75 flight time total : 2400 flight time type : 160
ASRS Report	320559
Person 2
Affiliation	company : air taxi
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : critical non adherence : published procedure other anomaly other other spatial deviation
Independent Detector	other controllera other flight crewa
Resolutory Action	flight crew : overcame equipment problem other other
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

While serving as first officer and flying pilot (PF) on an ILS approach into rdu, we experienced an instrument failure of the GS needle on the first officer's side leveling to a low glide path and a low altitude alert from tower. Both captain and first officer GS came alive at the same time and came to center evenly. After calling 'gear down-before landing checklist,' the approach seemed to be going well considering on GS, on-course, and correct rate of descent. The captain (PNF), while xchking his instruments, noticed that while the first officer's GS was centered, the captain's GS was at nearly full scale deflection. He immediately called 'stop the descent' and I obeyed. We broke out of the clouds and saw the runway at about the same time the tower said 'low altitude alert!' we said all was ok, runway in sight and we landed normally. After landing, the coplts GS was placarded inoperative and deferred as per the company MEL. Next time, the captain said he will monitor his side only. I don't think there was anything I could have done. I just flew the approach, the needles were wrong.

Original NASA ASRS Text

Title: FO'S GS FAILURE DURING AN ILS APCH HE WAS FLYING CAUSED A LOW ALT TWR ALERT.

Narrative: WHILE SERVING AS FO AND FLYING PLT (PF) ON AN ILS APCH INTO RDU, WE EXPERIENCED AN INSTRUMENT FAILURE OF THE GS NEEDLE ON THE FO'S SIDE LEVELING TO A LOW GLIDE PATH AND A LOW ALT ALERT FROM TWR. BOTH CAPT AND FO GS CAME ALIVE AT THE SAME TIME AND CAME TO CTR EVENLY. AFTER CALLING 'GEAR DOWN-BEFORE LNDG CHKLIST,' THE APCH SEEMED TO BE GOING WELL CONSIDERING ON GS, ON-COURSE, AND CORRECT RATE OF DSCNT. THE CAPT (PNF), WHILE XCHKING HIS INSTRUMENTS, NOTICED THAT WHILE THE FO'S GS WAS CTRED, THE CAPT'S GS WAS AT NEARLY FULL SCALE DEFLECTION. HE IMMEDIATELY CALLED 'STOP THE DSCNT' AND I OBEYED. WE BROKE OUT OF THE CLOUDS AND SAW THE RWY AT ABOUT THE SAME TIME THE TWR SAID 'LOW ALT ALERT!' WE SAID ALL WAS OK, RWY IN SIGHT AND WE LANDED NORMALLY. AFTER LNDG, THE COPLTS GS WAS PLACARDED INOP AND DEFERRED AS PER THE COMPANY MEL. NEXT TIME, THE CAPT SAID HE WILL MONITOR HIS SIDE ONLY. I DON'T THINK THERE WAS ANYTHING I COULD HAVE DONE. I JUST FLEW THE APCH, THE NEEDLES WERE WRONG.

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.