An air carrier freighter medium large transport crew had a low altitude alert on an ILS approach.

Attributes
ACN	257085
Time
Date	199311
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : pns
State Reference	FL
Altitude	agl bound lower : 500 agl bound upper : 500
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : pns
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent : approach
Route In Use	approach : straight in enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 150 flight time total : 5500 flight time type : 250
ASRS Report	257085
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : critical other spatial deviation
Independent Detector	other controllera
Resolutory Action	other other
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

While being vectored for the ILS runway 17 approach at pns, both navigation receivers were tuned and idented by myself. Localizer intercept occurred normally with a full 'fly up' GS indication on both GS indicators. Established on the localizer, both GS indicators came 'alive' and the aircraft was subsequently configured as per normal procedure. The glidepath was intercepted and followed normally. At approximately 500 ft AGL, the approach controller announced a 'low altitude alert' and a missed approach was initiated immediately. The controller stated our position as approximately 'brent' on the final approach course. We subsequently climbed back up to our vectoring altitude. I asked them to check their equipment and, at the same time, cycled my navigation receiver and retuned and idented my ILS frequency. My indicator #2 subsequently appeared normal and the #1 GS indicated erroneously (I.east, on GS with non flags) for our position (crosswind in the radar pattern). The following approach was flown after assessing my indicators as functional, without incident. The #1 navigation remained incorrect (on GS/no flags) throughout the approach. As for contributing factors, I cite mainly equipment failure, i.e., incorrect GS indications and #1 and #2 navigation indicators.

Original NASA ASRS Text

Title: AN ACR FREIGHTER MLG CREW HAD A LOW ALT ALERT ON AN ILS APCH.

Narrative: WHILE BEING VECTORED FOR THE ILS RWY 17 APCH AT PNS, BOTH NAV RECEIVERS WERE TUNED AND IDENTED BY MYSELF. LOC INTERCEPT OCCURRED NORMALLY WITH A FULL 'FLY UP' GS INDICATION ON BOTH GS INDICATORS. ESTABLISHED ON THE LOC, BOTH GS INDICATORS CAME 'ALIVE' AND THE ACFT WAS SUBSEQUENTLY CONFIGURED AS PER NORMAL PROC. THE GLIDEPATH WAS INTERCEPTED AND FOLLOWED NORMALLY. AT APPROX 500 FT AGL, THE APCH CTLR ANNOUNCED A 'LOW ALT ALERT' AND A MISSED APCH WAS INITIATED IMMEDIATELY. THE CTLR STATED OUR POS AS APPROX 'BRENT' ON THE FINAL APCH COURSE. WE SUBSEQUENTLY CLBED BACK UP TO OUR VECTORING ALT. I ASKED THEM TO CHK THEIR EQUIP AND, AT THE SAME TIME, CYCLED MY NAV RECEIVER AND RETUNED AND IDENTED MY ILS FREQ. MY INDICATOR #2 SUBSEQUENTLY APPEARED NORMAL AND THE #1 GS INDICATED ERRONEOUSLY (I.E, ON GS WITH NON FLAGS) FOR OUR POS (XWIND IN THE RADAR PATTERN). THE FOLLOWING APCH WAS FLOWN AFTER ASSESSING MY INDICATORS AS FUNCTIONAL, WITHOUT INCIDENT. THE #1 NAV REMAINED INCORRECT (ON GS/NO FLAGS) THROUGHOUT THE APCH. AS FOR CONTRIBUTING FACTORS, I CITE MAINLY EQUIP FAILURE, I.E., INCORRECT GS INDICATIONS AND #1 AND #2 NAV INDICATORS.

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.