Narrative:

We were vectored to the final approach course well outside the final approach fix for the ILS 24. We were solid IMC; and although I don't recall the precise conditions; it was night; approximately 500 overcast and several miles visibility; light winds; and drizzle. As we were on an intercept heading perhaps ten miles from the FAF we noticed that we did not have any glideslope indication. A little closer to centerline; the GS appeared; but was somewhat erratic in that it did not stay on the peg as one would expect at that range. At three to four miles from the FAF; the GS indication darted down to center; and the flight director captured it. The autopilot started a pitch down to follow the GS indication. All this happened very quickly. I called out a warning; as did the captain; and the sic/PF hit the toga switches to disengage the approach mode. This also commanded a pitch up and climb power. By the time the pitch; power; and configuration were returned to values appropriate to terminal area operations; the aircraft had climbed from the initial altitude of 2;000 to 2;700. This missed approach was announced to ATC as well as a report of the failed ILS signal. ATC responded that they did indeed have a failure light for the approach and would reset the system. We were vectored back to the procedure for a normal approach and landing.this was a situation that went from a hint of a potential issue to a full scale hazard in the blink of an eye. The PF [pilot flying] responded instinctively with the universal response to an approach gone wrong by commanding toga. However; as the initial and missed approaches share the same altitude; any missed approach climb before the final descent is initiated represents an altitude deviation.FD approach mode logic is structured to make inadvertent disengagement of the approach mode very difficult; and the approach mode is normally terminated with a landing. To disengage the approach mode prior to landing takes a procedure that; although quite simple; is never practiced and therefore is not a reflexive action. Another viable option would have been to disconnect the autopilot and ignore the FD while flying the plane raw data until the flight attendant/ap were reconfigured appropriately. Of course; timely notification of the failure from ATC would have been helpful as well. All these items were covered in our post flight debrief.the whole crew; as individuals; have also recommitted ourselves to greater diligence in day to day operations so that any future untoward events will not constitute such a surprise; allowing for quicker capture of errors and tighter margins to be maintained.

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Original NASA ASRS Text

Title: B747-400 First Officer and relief pilot reported executing a go-around after an altitude deviation on approach to WRI when the ILS signal malfunctioned.

Narrative: We were vectored to the final approach course well outside the final approach fix for the ILS 24. We were solid IMC; and although I don't recall the precise conditions; it was night; approximately 500 overcast and several miles visibility; light winds; and drizzle. As we were on an intercept heading perhaps ten miles from the FAF we noticed that we did not have any glideslope indication. A little closer to centerline; the GS appeared; but was somewhat erratic in that it did not stay on the peg as one would expect at that range. At three to four miles from the FAF; the GS indication darted down to center; and the flight director captured it. The autopilot started a pitch down to follow the GS indication. All this happened very quickly. I called out a warning; as did the captain; and the SIC/PF hit the TOGA switches to disengage the approach mode. This also commanded a pitch up and climb power. By the time the pitch; power; and configuration were returned to values appropriate to terminal area operations; the aircraft had climbed from the initial altitude of 2;000 to 2;700. This missed approach was announced to ATC as well as a report of the failed ILS signal. ATC responded that they did indeed have a failure light for the approach and would reset the system. We were vectored back to the procedure for a normal approach and landing.This was a situation that went from a hint of a potential issue to a full scale hazard in the blink of an eye. The PF [Pilot Flying] responded instinctively with the universal response to an approach gone wrong by commanding TOGA. However; as the initial and missed approaches share the same altitude; any missed approach climb before the final descent is initiated represents an altitude deviation.FD approach mode logic is structured to make inadvertent disengagement of the approach mode very difficult; and the approach mode is normally terminated with a landing. To disengage the approach mode prior to landing takes a procedure that; although quite simple; is never practiced and therefore is not a reflexive action. Another viable option would have been to disconnect the autopilot and ignore the FD while flying the plane raw data until the FA/AP were reconfigured appropriately. Of course; timely notification of the failure from ATC would have been helpful as well. All these items were covered in our post flight debrief.The whole crew; as individuals; have also recommitted ourselves to greater diligence in day to day operations so that any future untoward events will not constitute such a surprise; allowing for quicker capture of errors and tighter margins to be maintained.

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.