Narrative:

Ferry flight to reposition aircraft for return to passenger service. Aircraft was coming out of heavy maintenance phase. [We had an] uneventful takeoff and uneventful climb to FL370. Later; center directed us to descend from FL370 to FL330. As pilot not flying; I dialed in FL330 in the altitude box. The first officer; the flying pilot; engaged the vertical speed mode button on the flight control panel to commence descent. Vertical speed indication instantly jumped to 5;700 FPM climb rate. Aircraft was on autopilot; aircraft nose immediately started to rise comply with vsi. The first officer attempted to spin vertical speed wheel in negative direction to reduce vsi to a negative descent mode. However; vsi indicated climb was so high that after several attempts; he disengaged the autopilot; leveled out the aircraft to stop the climb and then pushed the nose over to commence descent to comply with ATC descent. By the time aircraft had leveled out and commenced descent; it had climbed 700 ft to 37;700 ft. Descent to FL330 was uneventful; reengaged autopilot and ATC did not query us about this altitude deviation. This event got our attention so we were closely observing our vertical speed mode for subsequent descents to see if this event would happen again during the remainder of the flight. We were given several altitudes to 'step down' in preparation for the arrival. The first officer used the vertical speed mode for these descents; worked normally; uneventful descents. Center descended us to cross an arrival fix at FL240. [We had an] uneventful descent using vertical speed mode. After the first fix; we were told to cross the next fix at 11;000. I dialed in this altitude; the first officer pushed vertical speed mode to descend aircraft. Vertical speed mode jumped to 4;000 ft rate of climb. The first officer immediately disengaged the vertical speed mode; used pitch mode to descend the aircraft to 11;000. We used the vertical speed mode for subsequent step down altitudes assigned to us by center. These descents were made using the vertical speed mode without any problems. [We had an] uneventful approach and landing. When we got to the gate; I wrote up this problem with the vertical speed mode in the aircraft maintenance log. I also notified maintenance of this problem. Mechanics came out to aircraft where I had a face to face brief to better explain the problems we had with the vertical speed mode. There was an apparent mechanical problem with vertical speed mode; possibly a problem with the 'rheostat' associated with the vertical speed wheel. I have been flying the crj-700 for over seven years; have never seen a problem like this with the vertical speed mode. Now that I have seen it; I'll be more aware of the potential problems with the vertical speed mode.

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Original NASA ASRS Text

Title: A CRJ700 autopilot twice jumped to climb rates of 5;700 FT and 4;000 FT per minute respectively after a lower altitude was set in the ALTITUDE SET and the Vertical Speed Mode engaged. A Vertical Speed Wheel rheostat malfunction was suspected.

Narrative: Ferry flight to reposition aircraft for return to passenger service. Aircraft was coming out of heavy maintenance phase. [We had an] uneventful takeoff and uneventful climb to FL370. Later; Center directed us to descend from FL370 to FL330. As pilot not flying; I dialed in FL330 in the altitude box. The First Officer; the Flying Pilot; engaged the Vertical Speed mode button on the Flight Control Panel to commence descent. Vertical Speed indication instantly jumped to 5;700 FPM climb rate. Aircraft was on autopilot; aircraft nose immediately started to rise comply with VSI. The First Officer attempted to spin vertical speed wheel in negative direction to reduce VSI to a negative descent mode. However; VSI indicated climb was so high that after several attempts; he disengaged the autopilot; leveled out the aircraft to stop the climb and then pushed the nose over to commence descent to comply with ATC descent. By the time aircraft had leveled out and commenced descent; it had climbed 700 FT to 37;700 FT. Descent to FL330 was uneventful; reengaged autopilot and ATC did not query us about this altitude deviation. This event got our attention so we were closely observing our Vertical Speed mode for subsequent descents to see if this event would happen again during the remainder of the flight. We were given several altitudes to 'step down' in preparation for the arrival. The First Officer used the Vertical Speed mode for these descents; worked normally; uneventful descents. Center descended us to cross an arrival fix at FL240. [We had an] uneventful descent using Vertical Speed mode. After the first fix; we were told to cross the next fix at 11;000. I dialed in this altitude; the First Officer pushed Vertical Speed mode to descend aircraft. Vertical Speed mode jumped to 4;000 FT rate of climb. The First Officer immediately disengaged the Vertical Speed mode; used pitch mode to descend the aircraft to 11;000. We used the Vertical Speed mode for subsequent step down altitudes assigned to us by Center. These descents were made using the Vertical Speed Mode without any problems. [We had an] uneventful approach and landing. When we got to the gate; I wrote up this problem with the Vertical Speed mode in the aircraft maintenance log. I also notified Maintenance of this problem. Mechanics came out to aircraft where I had a face to face brief to better explain the problems we had with the Vertical Speed mode. There was an apparent mechanical problem with Vertical Speed mode; possibly a problem with the 'rheostat' associated with the Vertical Speed wheel. I have been flying the CRJ-700 for over seven years; have never seen a problem like this with the Vertical Speed mode. Now that I have seen it; I'll be more aware of the potential problems with the Vertical Speed mode.

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.