Narrative:

Tracking inbound level at 4500 ft on the vhhh 25L localizer; cleared for the ILS approach. The glide slope diamond filled in; and came down normally; from above; and the autopilot captured it at about 1/2 dot. The airplane began descent out of 4500 ft. Then the glide slope became erratic and we got an amber bar through the FMA pitch indication. FMA reverted to V/south. Captain reset the F/D switches and re-selected approach mode. We noticed that our altitude was low for our position; but above briefed MSA; and we were below the RNAV path indication; and slowed the rate of descent toward level-off. Vhhh tower/approach then called and instructed us to climb back to 4500 ft; and to re-intercept glide path there. We began climb and re-intercepted glide slope at approximately 4000 ft. Captain hand flew the last part of the approach; and I noticed and commented that the localizer was jumpy as well - erratic.we briefed the glide slope issue. We anticipated 'jumpy' glide slope; but not a false capture; so when it came down normally from above; our reaction was 'so far so good' instead of cross checking our actual position in relation to a normal glide path. In other words; we were expecting to see something odd; but it looked normal. It captured normally; it was stable until going off-line altogether. This ILS should be fixed; or listed as unusable. A different carrier; we noticed; had requested the RNAV approach and we wondered why. We later concluded that that was 'local knowledge' and that the ILS was problematic enough to be avoided. The weather wasn't great; but on a dark and stormy night that ILS would be a real hazard.

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Original NASA ASRS Text

Title: B777 First Officer reported that the Hong Kong 25L glideslope became erratic and an amber bar appeared through the FMA pitch indication.

Narrative: Tracking inbound level at 4500 ft on the VHHH 25L localizer; cleared for the ILS approach. The glide slope diamond filled in; and came down normally; from above; and the autopilot captured it at about 1/2 dot. The airplane began descent out of 4500 ft. Then the glide slope became erratic and we got an amber bar through the FMA pitch indication. FMA reverted to V/S. Captain reset the F/D switches and re-selected approach mode. We noticed that our altitude was low for our position; but above briefed MSA; and we were below the RNAV path indication; and slowed the rate of descent toward level-off. VHHH tower/approach then called and instructed us to climb back to 4500 ft; and to re-intercept glide path there. We began climb and re-intercepted glide slope at approximately 4000 ft. Captain hand flew the last part of the approach; and I noticed and commented that the LOC was jumpy as well - erratic.We briefed the Glide Slope issue. We anticipated 'jumpy' glide slope; but not a false capture; so when it came down normally from above; our reaction was 'so far so good' instead of cross checking our actual position in relation to a normal glide path. In other words; we were expecting to see something odd; but it looked normal. It captured normally; it was stable until going off-line altogether. This ILS should be fixed; or listed as unusable. A different carrier; we noticed; had requested the RNAV approach and we wondered why. We later concluded that that was 'local knowledge' and that the ILS was problematic enough to be avoided. The weather wasn't great; but on a dark and stormy night that ILS would be a real hazard.

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.