Narrative:

I checked in with potomac approach and they descended us to 3000 feet and told us to expect vectors for the ILS 3 at kcho. Some minutes later they gave us a turn to a heading of 220. Correcting for the wind out of the west; this put us on a right downwind for runway 3. It surprised us because in the minutes leading up to this we had visual on the terrain below; including cars on the roads and building lights. It was not dark/invisible terrain. However I knew the safest thing would be to climb anyway. The autopilot came off but before the first officer (first officer) flying could really react much the warning stopped. We had only gained about 150 feet since the caution sounded. We didn't immediately know what had happened. In the past I had experienced RA malfunctions in the [erj] that had produced false landing gear warnings; bank angle warnings; ground prox warnings etc and I considered if that had happened but the RA seemed to be working okay. It showed us slowly fluctuating in the range of about 1900-2300 AGL at 3000 MSL. Field elevation at kcho nearby is 640 feet MSL. As we approached the point where we would be abeam the field; ATC asked us to say our flight conditions. I replied that we were in VMC but could not yet see the field. The controller asked us if we wanted a vector to a visual or the ILS. The first officer and I agreed we wanted the ILS. I told ATC this and they acknowledged. During this time we were looking off our right or 2 o clock position a lot; trying to make out the field position. Soon after this; the egpws gave us a ground prox caution box in the pfd attitude indicator area and an aural 'terrain terrain pull up!' when I looked over at my ipad approach plate; my geo-referenced aircraft symbol showed us and our track having just passed over an obstacle/tower labeled 1795 feet just east of kcho near the missed approach track line. I then theorized that our RA might have bounced a wave off this probably metal tower and received enough beam back to cause our RA to read about 1200 feet; an instant drop of hundreds of feet. This led the egpws to trigger a warning due either to us not being configured for landing; or due to the egpws calculating a false rapid rise in terrain; and possibly coupled with the egpws database knowing that tower was there very close by. Possibly an ATC change to raise the minimum vectoring altitude there; and/or a wider downwind closer to gve VOR to avoid the possibility of this false warning.

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Original NASA ASRS Text

Title: ERJ flight crew reported receiving a terrain warning while on radar vectors for a visual approach to CHO; likely due to a nearby tower.

Narrative: I checked in with Potomac Approach and they descended us to 3000 feet and told us to expect vectors for the ILS 3 at KCHO. Some minutes later they gave us a turn to a heading of 220. Correcting for the wind out of the west; this put us on a right downwind for Runway 3. It surprised us because in the minutes leading up to this we had visual on the terrain below; including cars on the roads and building lights. It was not dark/invisible terrain. However I knew the safest thing would be to climb anyway. The autopilot came off but before the FO (First Officer) flying could really react much the warning stopped. We had only gained about 150 feet since the caution sounded. We didn't immediately know what had happened. In the past I had experienced RA malfunctions in the [ERJ] that had produced false landing gear warnings; bank angle warnings; ground prox warnings etc and I considered if that had happened but the RA seemed to be working okay. It showed us slowly fluctuating in the range of about 1900-2300 AGL at 3000 MSL. Field elevation at KCHO nearby is 640 feet MSL. As we approached the point where we would be abeam the field; ATC asked us to say our flight conditions. I replied that we were in VMC but could not yet see the field. The controller asked us if we wanted a vector to a visual or the ILS. The FO and I agreed we wanted the ILS. I told ATC this and they acknowledged. During this time we were looking off our right or 2 o clock position a lot; trying to make out the field position. Soon after this; the EGPWS gave us a Ground Prox caution box in the PFD attitude indicator area and an Aural 'Terrain terrain pull up!' When I looked over at my IPad approach plate; my Geo-Referenced aircraft symbol showed us and our track having just passed over an obstacle/tower labeled 1795 feet just east of KCHO near the missed approach track line. I then theorized that our RA might have bounced a wave off this probably metal tower and received enough beam back to cause our RA to read about 1200 feet; an instant drop of hundreds of feet. This led the EGPWS to trigger a warning due either to us not being configured for landing; or due to the EGPWS calculating a false rapid rise in terrain; and possibly coupled with the EGPWS database knowing that tower was there very close by. Possibly an ATC change to raise the Minimum vectoring altitude there; and/or a wider downwind closer to GVE VOR to avoid the possibility of this false warning.

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.