Narrative:

On visual approach for runway 17 at far, copilot was flying and using the ILS as a backup for a visual. I noticed he was slightly low on VASI (or PAPI, whichever it is) at approximately 1000 ft AGL. He continued to go around lower and I noticed the ILS GS indicated we were high. It was wrong, we were low as correctly indicated by the VASI/PAPI. We told far ground controller. He said he would check it out. The next week he reported to us that the ILS had been getting maintenance earlier in the day. Apparently some cables were reconnected to the wrong terminals, in effect causing reverse sensing on the GS. No warning of this condition was generated. Obviously, this is dangerous and must be prevented in the future by redesigning the system.

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Original NASA ASRS Text

Title: REVERSE SENSING OF THE GS CAUSES MLG TO DSND BELOW THE GS AT FAR.

Narrative: ON VISUAL APCH FOR RWY 17 AT FAR, COPLT WAS FLYING AND USING THE ILS AS A BACKUP FOR A VISUAL. I NOTICED HE WAS SLIGHTLY LOW ON VASI (OR PAPI, WHICHEVER IT IS) AT APPROX 1000 FT AGL. HE CONTINUED TO GAR LOWER AND I NOTICED THE ILS GS INDICATED WE WERE HIGH. IT WAS WRONG, WE WERE LOW AS CORRECTLY INDICATED BY THE VASI/PAPI. WE TOLD FAR GND CTLR. HE SAID HE WOULD CHK IT OUT. THE NEXT WK HE RPTED TO US THAT THE ILS HAD BEEN GETTING MAINT EARLIER IN THE DAY. APPARENTLY SOME CABLES WERE RECONNECTED TO THE WRONG TERMINALS, IN EFFECT CAUSING REVERSE SENSING ON THE GS. NO WARNING OF THIS CONDITION WAS GENERATED. OBVIOUSLY, THIS IS DANGEROUS AND MUST BE PREVENTED IN THE FUTURE BY REDESIGNING THE SYS.

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.