Narrative:

Level at fl 120 and slowing to 250 knots per approach request when amber solid block TCAS traffic appeared on display 11 -12 o'clock at approx. 5 NM range and 500 feet of separation. Verbalized traffic to first officer (first officer) to ensure he was aware that it had popped up on TCAS. Both first officer and I visually scanned for traffic. Soon thereafter TCAS 'traffic; traffic' aural. TCAS RA commanded 'climb; climb'. At some time here I noticed only 400 feet of separation now displayed; indicating conflicting traffic possibly in a climb. After initiating climb TCAS quickly thereafter commanded 'increase climb'. I pitched to the top of the vsi scale which had the small green block at the very top of the scale; with the remainder in red. Very soon after achieving pitch at top of vsi; the TCAS commanded 'descend; descend'. This was a big surprise. Had the other aircraft climbed also? Was there another aircraft above us now? As I pitched down I asked the first officer if he had the aircraft visually. I believe he may have said no. I scanned the vsi and all I could interpret from a brief look was red outline. Where was the green? I looked at the mfd and the target was close but still to our left. To aid the rate of descent and provide necessary vertical separation in a deteriorating situation I elected to turn to the right. As I started the turn I caught sight of the high-wing small aircraft at 10-11 o'clock and below our altitude so I stopped descending. A second or two later ATC issued us a 'right turn heading 270 deg.' clearance so I kept the airplane turning to that heading while maintaining vertical separation. When I queried approach after the event they confirmed traffic was VFR. At no time were we issued a traffic advisory for this traffic prior to the event. A minute or so after event [the small aircraft] contacted approach in a manner that suggested that they may have already established radio contact. '[Approach] is everything ok now?' or words to that effect. Approach just replied 'yes'. The same controller asked us if we had responded to a TCAS alert. Within a few minutes this male controller's voice was replaced by a female controller for the remainder of our transition to tower control for landing. If possible I would like to get feedback of any further information that may be available to help explain the TCAS commanding a climb and then a descent.

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Original NASA ASRS Text

Title: CRJ-700 Captain at 12;000 feet experienced a TCAS RA with a small aircraft 500 feet below. The TCAS commanded a Climb Climb then an 'Increase climb'; followed quickly by 'Descend; Descend.' In the end it appeared that the light aircraft had never changed altitude.

Narrative: Level at FL 120 and slowing to 250 knots per Approach request when amber solid block TCAS traffic appeared on display 11 -12 o'clock at approx. 5 NM range and 500 feet of separation. Verbalized traffic to FO (First Officer) to ensure he was aware that it had popped up on TCAS. Both FO and I visually scanned for traffic. Soon thereafter TCAS 'TRAFFIC; TRAFFIC' aural. TCAS RA commanded 'CLIMB; CLIMB'. At some time here I noticed only 400 feet of separation now displayed; indicating conflicting traffic possibly in a climb. After initiating climb TCAS quickly thereafter commanded 'INCREASE CLIMB'. I pitched to the top of the VSI scale which had the small green block at the very top of the scale; with the remainder in red. Very soon after achieving pitch at top of VSI; the TCAS commanded 'DESCEND; DESCEND'. This was a big surprise. Had the other aircraft climbed also? Was there another aircraft above us now? As I pitched down I asked the FO if he had the aircraft visually. I believe he may have said no. I scanned the VSI and all I could interpret from a brief look was Red outline. Where was the green? I looked at the MFD and the target was close but still to our left. To aid the rate of descent and provide necessary vertical separation in a deteriorating situation I elected to turn to the right. As I started the turn I caught sight of the high-wing small aircraft at 10-11 o'clock and below our altitude so I stopped descending. A second or two later ATC issued us a 'right turn heading 270 deg.' clearance so I kept the airplane turning to that heading while maintaining vertical separation. When I queried Approach after the event they confirmed traffic was VFR. At no time were we issued a traffic advisory for this traffic prior to the event. A minute or so after event [the small aircraft] contacted Approach in a manner that suggested that they may have already established radio contact. '[Approach] is everything OK now?' or words to that effect. Approach just replied 'Yes'. The same controller asked us if we had responded to a TCAS alert. Within a few minutes this male controller's voice was replaced by a female controller for the remainder of our transition to Tower control for landing. If possible I would like to get feedback of any further information that may be available to help explain the TCAS commanding a climb and then a descent.

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.