An air carrier at 2500 ft 5 miles from BUF on an ILS Runway 23 localizer intercept heading from the north pitched up 18 degrees and climbed to 3000 ft. A rapid power application to counter the slowing airspeed contributed to the pitch up and 10 kt airspeed loss.

Narrative

Glideslope anomaly while being vectored for ILS Runway 23 at BUF. Altitude deviation. Weather in BUF was 40 RVR and required an ILS approach to Runway 23. NOTAMS indicated the glideslope was unusable 5 degrees right of course. Our vectors placed us in this area with a right base for Runway 23. Configuration was flaps 5. Instructions for intercept were; 'Maintain 2500 ft until established; cleared ILS Runway 23 approach.' Once cleared for the approach; 'Approach Mode' was selected. During the vector to final the glideslope was at the bottom of the case indicating 2 dots. This implied we were high. We were aware of the NOTAM and confirmed 5 miles to glideslope intercept altitude; which meant we had 5 miles to lose 300 ft. We were being vectored below glideslope for a normal glideslope intercept. At localizer intercept or very near; the glideslope started moving from the bottom of the case upward. As it approached 'on glideslope' the flight director/autopilot captured it. The glideslope continued to rise in the case causing the autopilot to follow. The First Officer immediately noticed what had happened and stated; 'You are climbing.' The rate of the glideslope moving from the bottom of the case to the top of the case was fairly quick. As the aircraft pitched up and followed the glideslope; the airspeed began to decrease. I disconnected the autopilot and added power. This caused the aircraft to pitch up further. Forward trim and forward pressure on the yoke transitioned the aircraft nicely on a corrective flight path. Airspeed decreased to about 10 knots below our flaps 5 configuration and altitude climbed to approximately 3000 ft from 2500 ft. Deviations of approximately 10 knots slow and 500 ft high. Once acceptable parameters were recaptured; the approach was continued. All stabilized criteria were met prior to glideslope intercept altitude. Dispatch; Safety and Flight Operations was notified immediately. The purpose and intent of this report is to not only fulfill the obligations to report deviations; but to prevent other crews from the potential of such an occurrence.Callback conversation with reporter revealed the following info: The reporter's factual data was provided after a review of the aircraft's FOQA data. The actual pitch angle achieved was 18 degrees. The reporter stated that he saw the aircraft pitch up before the Captain whose initial response was to the airspeed decrease. Because of the large and rapid power increase the pitch was possibly more pronounced than it may have otherwise been. After recovery; the aircraft was configured and on glideslope at the final approach fix. The event was not reported to ATC because the crew thought that it was caused by an aircraft malfunction and did not realize until later that the cause may have been the glide slope. The reporter was surprised that ATC did not comment on this event and the crew did not report it. The reporter stated that he met another pilot that night; who stated that his flight had the same event happen that afternoon and also did not report it.