A CRJ90 Captain returned to the departure airport after the right engine vibration meter increased into the amber region. An emergency was declared for the return; which was uneventful.

Narrative

While climbing to our cruise altitude; passing approximately FL280; we noted the number 2 (right) engine fan vibration gauge indication trending steadily upward. Before long the readout went into the amber caution range. I immediately started slowly retarding the number 2 thrust lever in an attempt to control the fan vibration. I then called for the QRH to address fan vibrations; leveled off our climb rate and requested from ATC a slow descent. As the second in command ran the QRH; the vibration indications fluctuated but eventually dropped into the green range only with the engine at idle. I decided we would not be able to continue to our destination. I advised ATC we would need to return to departure point and declared an emergency. We were immediately vectored back. Flight attendants and passengers were advised of the situation and told to expect an uneventful arrival. Based on previous experience with engine-at-idle operations and ambient field and weather conditions; I decided to treat the approach and landing as if they were single-engine operation; with the number 2 engine at idle. We conducted the approach and landing with reduced flaps; increased approach speed and landing distance in good VMC and a dry runway. Our arrival was uneventful and the emergency was canceled as we cleared the runway. There is no substantive guidance in the QRH on 'the next step' after an engine vibe is brought under control without shutting the engine down. This goes back to the pilot in command to decide; based on Operation's Manual guidance and prudence to make a decision to continue or divert for landing. In this case; due to the close proximity of the departure airport and good weather conditions; it was decided to return to land there. Based on previous experience with one-engine-at-engine-idle operations; a decision against full flap approach and landing was made. Selected portions of the single-engine QRH guidance were used for a safe; reduced flap approach and landing.