Narrative:

On approach into cho we were being vectored onto the ILS 3. We were at 3000 when we were given a clearance of 'turn right 360 to intercept maintain 3000 till established clear ILS 3.' once on the 360 heading the autopilot captured the localizer and glide slope simultaneously. This caught me off guard because my HSI was not displaying a glide slope indication. I looked over to my first officer's HSI (first officer was the PF) and his showed us tracking on glide slope and both sides had a good identification. At that point I assumed there was something wrong with my glide slope indication; however it was not flagged; the glide slope was simply out of view. Upon cross checking our altitude with the DME I saw that we were well below that glide slope and that the indication on the first officer HSI had to be wrong. It was at that point that ATC advised us that we were below the glide slope and issued us a low altitude alert; to which I replied 'correcting.' as I was replying to ATC we picked up the field visually. I called the field in sight and we were cleared for the visual. Once on the ground I called mx and wrote up the first officer glide slope indication. Upon conference with mx I learned that the aircraft had a history of first officer side ILS indication issues. This event occurred because of a mechanical issue with the first officer side navigation equipment. This event took longer than it should have to detect and remedy; because I as PIC and pilot monitoring was feeling the effects of fatigue. It was day 4 that had me working all across the system; going from mornings to nights; with multiple different crews and I had been on duty for almost 12 hours. I believe that if I was not so tired I would have had a better grasp of the big picture and been able to detect the problem and intervene before it became an issue. There is a fatigue report associated with this as soon as possible.these ILS issues seem to be becoming more frequent in [our] fleet. In the future; I will be more vigilant of where we are and what altitude we should be at; also I will level off and stop the descent at the first sign of the hsis disagreeing.

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Original NASA ASRS Text

Title: Air carrier flight crew reported descending below the glideslope on approach to CHO when the First Officer's glideslope indications were erroneous.

Narrative: On approach into CHO we were being vectored onto the ILS 3. We were at 3000 when we were given a clearance of 'turn right 360 to intercept maintain 3000 till established clear ILS 3.' Once on the 360 heading the autopilot captured the LOC and glide slope simultaneously. This caught me off guard because my HSI was not displaying a glide slope indication. I looked over to my FO's HSI (FO was the PF) and his showed us tracking on glide slope and both sides had a good ID. At that point I assumed there was something wrong with my glide slope indication; however it was not flagged; the glide slope was simply out of view. Upon cross checking our altitude with the DME I saw that we were well below that glide slope and that the indication on the FO HSI had to be wrong. It was at that point that ATC advised us that we were below the glide slope and issued us a low altitude alert; to which I replied 'correcting.' As I was replying to ATC we picked up the field visually. I called the field in sight and we were cleared for the visual. Once on the ground I called MX and wrote up the FO glide slope indication. Upon conference with MX I learned that the aircraft had a history of FO side ILS indication issues. This event occurred because of a mechanical issue with the FO side NAV equipment. This event took longer than it should have to detect and remedy; because I as PIC and pilot monitoring was feeling the effects of fatigue. It was day 4 that had me working all across the system; going from mornings to nights; with multiple different crews and I had been on duty for almost 12 hours. I believe that if I was not so tired I would have had a better grasp of the big picture and been able to detect the problem and intervene before it became an issue. There is a fatigue report associated with this ASAP.These ILS issues seem to be becoming more frequent in [our] fleet. In the future; I will be more vigilant of where we are and what ALT we should be at; also I will level off and stop the descent at the first sign of the HSIs disagreeing.

Data retrieved from NASA's ASRS site 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.