Narrative:

After takeoff leaving 8000 ft, the cabin called and seconds later called again. The #3 said there was an unusual noise/vibration coming from the right side of the aircraft by the engine. We checked the engine instruments and everything was normal. Since the #3 was concerned to get my immediate attention during the sterile period, I immediately went to the back of the aircraft and the vibration increased, I went back to the cockpit and noticed the right N1 needle vibrating. ATC was informed that we needed to level off and I disconnected the autothrottles and reduced power to 1.2 EPR. The vibration stopped in the cockpit. I called back to the #3 and she told me it was better. We declared an emergency and returned to dfw. Not knowing specifically what caused the vibration and the possibility it was ice ingestion, there was a remote chance the same could occur to the left engine. Since the right engine was producing power and all engine indications were normal at that power setting, I elected to maintain use of the engine. We reviewed the QRH and landed with 28 flaps. The aircraft was deiced and inspected by a certified deicer. The maintenance personnel suspect ice ingestion. The fan blades were destroyed. I was informed I was the fifth aircraft with this problem that night. We were on the ramp for 3 hours before we were deiced. Supplemental information from acn 257626: we elected not to shut down the right engine since it stopped showing erratic signs once power was reduced for descent.

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Original NASA ASRS Text

Title: THE #2 ENG ON AN ACR MLG WAS LOST TO FOREIGN OBJECT DAMAGE.

Narrative: AFTER TKOF LEAVING 8000 FT, THE CABIN CALLED AND SECONDS LATER CALLED AGAIN. THE #3 SAID THERE WAS AN UNUSUAL NOISE/VIBRATION COMING FROM THE R SIDE OF THE ACFT BY THE ENG. WE CHKED THE ENG INSTS AND EVERYTHING WAS NORMAL. SINCE THE #3 WAS CONCERNED TO GET MY IMMEDIATE ATTN DURING THE STERILE PERIOD, I IMMEDIATELY WENT TO THE BACK OF THE ACFT AND THE VIBRATION INCREASED, I WENT BACK TO THE COCKPIT AND NOTICED THE R N1 NEEDLE VIBRATING. ATC WAS INFORMED THAT WE NEEDED TO LEVEL OFF AND I DISCONNECTED THE AUTOTHROTTLES AND REDUCED PWR TO 1.2 EPR. THE VIBRATION STOPPED IN THE COCKPIT. I CALLED BACK TO THE #3 AND SHE TOLD ME IT WAS BETTER. WE DECLARED AN EMER AND RETURNED TO DFW. NOT KNOWING SPECIFICALLY WHAT CAUSED THE VIBRATION AND THE POSSIBILITY IT WAS ICE INGESTION, THERE WAS A REMOTE CHANCE THE SAME COULD OCCUR TO THE L ENG. SINCE THE R ENG WAS PRODUCING PWR AND ALL ENG INDICATIONS WERE NORMAL AT THAT PWR SETTING, I ELECTED TO MAINTAIN USE OF THE ENG. WE REVIEWED THE QRH AND LANDED WITH 28 FLAPS. THE ACFT WAS DEICED AND INSPECTED BY A CERTIFIED DEICER. THE MAINT PERSONNEL SUSPECT ICE INGESTION. THE FAN BLADES WERE DESTROYED. I WAS INFORMED I WAS THE FIFTH ACFT WITH THIS PROB THAT NIGHT. WE WERE ON THE RAMP FOR 3 HRS BEFORE WE WERE DEICED. SUPPLEMENTAL INFO FROM ACN 257626: WE ELECTED NOT TO SHUT DOWN THE R ENG SINCE IT STOPPED SHOWING ERRATIC SIGNS ONCE PWR WAS REDUCED FOR DSCNT.

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.