Flight Crew Instrument; Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Flight Crew Last 90 Days 245; Flight Crew Total 19429; Flight Crew Type 1515
Situational Awareness
Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance
Flight Crew Executed Go Around / Missed Approach
ATC Equipment / Nav Facility / Buildings; Human Factors
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.
[Report narrative contained no additional information].
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.