EMB ERJ 145 ER/LR
Flight Crew Air Transport Pilot (ATP)
Troubleshooting
Aircraft Equipment Problem Critical
General Declared Emergency; General Maintenance Action
Aircraft; Procedure
We were cleared to descend from 12;000 FT to 8;000 FT with Approach Control. As I moved the thrust levers to flight idle to start the descent and slow the aircraft to 250 KTS; the right engine began to cause a vibration in the cockpit (below 45% N1). As we passed through 10;000 FT the #2 engine oil pressure dropped into the red range (24-26 PSI). The First Officer immediately declared an emergency to get us heading directly to the airport. Having written up the vibrations on the previous flight; we knew that the vibrations would go away above 45% N1. We increased the thrust to 46% and the oil pressure went to the bottom on the green range and the vibrations stopped. First Officer also read the 'Engine Low Oil Pressure Checklist' which did not apply to our situation. We continued to the airport with 46-48% N1 to maintain oil pressure until above the runway; where we returned to flight idle and landed the aircraft.Maintenance did their usual 'Ops Check Good' when we wrote it up in [departure station]. I asked Maintenance Control what I should do; ignore the vibrations? He said there was nothing they could do because there weren't any EICAS messages and they couldn't see anything in the front or back of the engine. He told me to monitor the engine parameters and if they got worse; call.
EMB-145 Captain reported right engine vibration and low oil pressure on descent. Emergency was declared and a safe landing ensued.