Narrative:

We were on vectors to intercept dal runway 31R localizer at assigned 2;400 ft MSL. The autopilot was engaged. We intercepted the localizer with a tailwind and aggressive angle of intercept (late turn by ATC; in my opinion). The pilot flying selected appch mode and the localizer captured; but overshot into the approach corridor for runway 31L. Simultaneously; the avionics indicated a glideslope capture. Position was 10 NM final and since we were 1;100 ft below the glideslope beam; the aircraft pitched up about 5 degrees and began a climb. I directed the pilot flying to disconnect the autopilot; that a 'false glideslope had been captured.' by the time he did this the aircraft was 600 ft high (3;000 ft MSL) and flying towards runway 31L. I told the pilot flying to descend back down to 2;400 ft and turn right towards the ILS 31R. I estimate our deviation time from 2;400 ft MSL and the 31R localizer to be 45 seconds. No TCAS warnings or ATC query were made. I know of no conflicts to other traffic. The 31R localizer and glideslope were recaptured and a normal approach and landing occurred.my opinion is that the glideslope signal on our landing runway (31R) fluctuated - perhaps due to aircraft taxiing through the critical zone. I recall seeing the glideslope pop down (case break) and then go back up off the HSI. I believe the avionics captured this signal and the aircraft pitched up to maintain the glideslope (even though we were 1;000+ ft below the normal glide path). I will keep a vigilant watch for false captures of the glideslope on dal 31R. Other pilots familiar with this airport report past fluctuations of this glideslope.

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Original NASA ASRS Text

Title: G200 Captain reports capturing a false glideslope during LOC intercept of Runway 31R ILS at DAL. False signal causes autopilot to pitch up and gain 600 FT before pilot flying returns aircraft to assigned altitude. LOC deviations are also reported possibly due to late turn to intercept and tailwinds.

Narrative: We were on vectors to intercept DAL Runway 31R localizer at assigned 2;400 FT MSL. The autopilot was engaged. We intercepted the localizer with a tailwind and aggressive angle of intercept (late turn by ATC; in my opinion). The pilot flying selected APPCH mode and the LOC captured; but overshot into the approach corridor for Runway 31L. Simultaneously; the avionics indicated a glideslope capture. Position was 10 NM final and since we were 1;100 FT below the glideslope beam; the aircraft pitched up about 5 degrees and began a climb. I directed the pilot flying to disconnect the autopilot; that a 'false glideslope had been captured.' By the time he did this the aircraft was 600 FT high (3;000 FT MSL) and flying towards Runway 31L. I told the pilot flying to descend back down to 2;400 FT and turn right towards the ILS 31R. I estimate our deviation time from 2;400 FT MSL and the 31R localizer to be 45 seconds. No TCAS warnings or ATC query were made. I know of no conflicts to other traffic. The 31R localizer and glideslope were recaptured and a normal approach and landing occurred.My opinion is that the glideslope signal on our landing runway (31R) fluctuated - perhaps due to aircraft taxiing through the critical zone. I recall seeing the glideslope pop down (case break) and then go back up off the HSI. I believe the avionics captured this signal and the aircraft pitched up to maintain the glideslope (even though we were 1;000+ FT below the normal glide path). I will keep a vigilant watch for false captures of the glideslope on DAL 31R. Other pilots familiar with this airport report past fluctuations of this glideslope.

Data retrieved from NASA's ASRS site as of April 2012 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.