Narrative:

This statement concerns a part 121 scheduled air carrier flight operated in an SF340B aircraft which departed pvd and arrived lga. I was the captain and the PF. The takeoff, climb and initial cruise segment of the flight were normal and uneventful. During cruise while over mad VOR we noticed a decrease of propeller RPM and an increase of torque on the left engine. We performed the erratic engine operation checklist followed by the propeller RPM underspd checklist. At this time we notified ATC that while our left engine was still producing power, we were experiencing erratic left propeller RPM, all other engine indications were normal and we requested to be cleared direct to lga. ATC immediately cleared us direct lga and we proceeded as cleared at 8000 ft MSL. I xferred control of the aircraft and communication #1 radio communications to the first officer and contacted company maintenance on communication #2. Maintenance suggested that we lock out the torque motor, which we had already done, and check for popped circuit breakers. No circuit breakers were popped, maintenance had no further suggestions. I then briefed the flight attendant over the intercom followed by the passenger over the PA. When I returned to cockpit communications, the first officer was descending to 4000 ft and speaking to lga approach control. Lga approach told us to expect the expressway visual runway 31 approach. We informed lga approach that we wanted to enter a right base for runway 31 and declared an emergency to facilitate priority handling. I took control of the aircraft from the first officer and we completed the descent, approach, and before landing checklists. The approach and landing were made without further incident.

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Original NASA ASRS Text

Title: AN SF340 FLC ENRTE FROM PVD TO LGA DECLARED AN EMER AFTER OBSERVING ERRATIC PROP RPM.

Narrative: THIS STATEMENT CONCERNS A PART 121 SCHEDULED ACR FLT OPERATED IN AN SF340B ACFT WHICH DEPARTED PVD AND ARRIVED LGA. I WAS THE CAPT AND THE PF. THE TKOF, CLB AND INITIAL CRUISE SEGMENT OF THE FLT WERE NORMAL AND UNEVENTFUL. DURING CRUISE WHILE OVER MAD VOR WE NOTICED A DECREASE OF PROP RPM AND AN INCREASE OF TORQUE ON THE L ENG. WE PERFORMED THE ERRATIC ENG OP CHKLIST FOLLOWED BY THE PROP RPM UNDERSPD CHKLIST. AT THIS TIME WE NOTIFIED ATC THAT WHILE OUR L ENG WAS STILL PRODUCING PWR, WE WERE EXPERIENCING ERRATIC L PROP RPM, ALL OTHER ENG INDICATIONS WERE NORMAL AND WE REQUESTED TO BE CLRED DIRECT TO LGA. ATC IMMEDIATELY CLRED US DIRECT LGA AND WE PROCEEDED AS CLRED AT 8000 FT MSL. I XFERRED CTL OF THE ACFT AND COM #1 RADIO COMS TO THE FO AND CONTACTED COMPANY MAINT ON COM #2. MAINT SUGGESTED THAT WE LOCK OUT THE TORQUE MOTOR, WHICH WE HAD ALREADY DONE, AND CHK FOR POPPED CIRCUIT BREAKERS. NO CIRCUIT BREAKERS WERE POPPED, MAINT HAD NO FURTHER SUGGESTIONS. I THEN BRIEFED THE FLT ATTENDANT OVER THE INTERCOM FOLLOWED BY THE PAX OVER THE PA. WHEN I RETURNED TO COCKPIT COMS, THE FO WAS DSNDING TO 4000 FT AND SPEAKING TO LGA APCH CTL. LGA APCH TOLD US TO EXPECT THE EXPRESSWAY VISUAL RWY 31 APCH. WE INFORMED LGA APCH THAT WE WANTED TO ENTER A R BASE FOR RWY 31 AND DECLARED AN EMER TO FACILITATE PRIORITY HANDLING. I TOOK CTL OF THE ACFT FROM THE FO AND WE COMPLETED THE DSCNT, APCH, AND BEFORE LNDG CHKLISTS. THE APCH AND LNDG WERE MADE WITHOUT FURTHER INCIDENT.

Data retrieved from NASA's ASRS site as of July 2007 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.