Narrative:

I experienced a severe flutter in the pitch axis while in cruise flight at FL190 and 315 KIAS. We were IMC; but there was no icing whatsoever. Turbulence was occasionally moderate in magnitude; and at first I thought the flutter was just more turbulence; but it increased gradually in magnitude over a period of a few seconds; and was of a very rhythmic quality that it could not have been the result of turbulence. I reduced speed from 315 KTS to 290 KTS immediately; and as I did so; the autoplt disconnected by itself; with 'autoplt failure EICAS' message. The entire episode lasted 10-15 seconds. After about 1 min; I re-engaged the autoplt; and continued the flight normally at a slightly reduced speed. The flutter never recurred; and there were no other problems encountered. I did not declare an emergency; and the flight proceeded without incident to bos. There was no indication of any damage to the aircraft; including the flight controls. The flutter was noticeable to the flight attendant. I reported the event to maintenance; and wrote it up in the maintenance log. The aircraft was removed from service for 3 days. I was interviewed about the incident by the bos maintenance supervisor; and by director of flight operations (line). I operated the aircraft at 315 KTS because 1) we were assigned '300 KTS or better' by ATC; and told we were 'leading the pack' into bos. 2) our aom says there is 'little use' to flying at a slower speed in other than severe turbulence. At no time did the turbulence approach 'severe' magnitude. Detection: the flutter was obvious: rhythmic vibration in the pitch axis of about 4 hertz; roughly. Reaction: reduced speed; checked control effectiveness; re-engaged autoplt; hand flew the approach. Callback conversation with reporter revealed the following information: the pilot's air carrier maintenance could find no discrepancy causing this problem. Reporter stated that while discussing his experience; other pilots have reported the brief high speed flutter with the autoplt engaged. The event was brief and the crew not frightened; but concerned.

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Original NASA ASRS Text

Title: AN EMB135 EXPERIENCED A 15 SECOND LONGITUDINAL FLUTTER AT FL190 AND 315 KTS. WITH THE AUTOPLT DISCONNECTED AND ACFT SLOWED; THE FLUTTER CEASED.

Narrative: I EXPERIENCED A SEVERE FLUTTER IN THE PITCH AXIS WHILE IN CRUISE FLT AT FL190 AND 315 KIAS. WE WERE IMC; BUT THERE WAS NO ICING WHATSOEVER. TURB WAS OCCASIONALLY MODERATE IN MAGNITUDE; AND AT FIRST I THOUGHT THE FLUTTER WAS JUST MORE TURB; BUT IT INCREASED GRADUALLY IN MAGNITUDE OVER A PERIOD OF A FEW SECONDS; AND WAS OF A VERY RHYTHMIC QUALITY THAT IT COULD NOT HAVE BEEN THE RESULT OF TURB. I REDUCED SPD FROM 315 KTS TO 290 KTS IMMEDIATELY; AND AS I DID SO; THE AUTOPLT DISCONNECTED BY ITSELF; WITH 'AUTOPLT FAILURE EICAS' MESSAGE. THE ENTIRE EPISODE LASTED 10-15 SECONDS. AFTER ABOUT 1 MIN; I RE-ENGAGED THE AUTOPLT; AND CONTINUED THE FLT NORMALLY AT A SLIGHTLY REDUCED SPD. THE FLUTTER NEVER RECURRED; AND THERE WERE NO OTHER PROBS ENCOUNTERED. I DID NOT DECLARE AN EMER; AND THE FLT PROCEEDED WITHOUT INCIDENT TO BOS. THERE WAS NO INDICATION OF ANY DAMAGE TO THE ACFT; INCLUDING THE FLT CTLS. THE FLUTTER WAS NOTICEABLE TO THE FLT ATTENDANT. I RPTED THE EVENT TO MAINT; AND WROTE IT UP IN THE MAINT LOG. THE ACFT WAS REMOVED FROM SVC FOR 3 DAYS. I WAS INTERVIEWED ABOUT THE INCIDENT BY THE BOS MAINT SUPVR; AND BY DIRECTOR OF FLT OPS (LINE). I OPERATED THE ACFT AT 315 KTS BECAUSE 1) WE WERE ASSIGNED '300 KTS OR BETTER' BY ATC; AND TOLD WE WERE 'LEADING THE PACK' INTO BOS. 2) OUR AOM SAYS THERE IS 'LITTLE USE' TO FLYING AT A SLOWER SPD IN OTHER THAN SEVERE TURB. AT NO TIME DID THE TURB APPROACH 'SEVERE' MAGNITUDE. DETECTION: THE FLUTTER WAS OBVIOUS: RHYTHMIC VIBRATION IN THE PITCH AXIS OF ABOUT 4 HERTZ; ROUGHLY. REACTION: REDUCED SPD; CHKED CTL EFFECTIVENESS; RE-ENGAGED AUTOPLT; HAND FLEW THE APCH. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE PLT'S ACR MAINT COULD FIND NO DISCREPANCY CAUSING THIS PROB. RPTR STATED THAT WHILE DISCUSSING HIS EXPERIENCE; OTHER PLTS HAVE RPTED THE BRIEF HIGH SPD FLUTTER WITH THE AUTOPLT ENGAGED. THE EVENT WAS BRIEF AND THE CREW NOT FRIGHTENED; BUT CONCERNED.

Data retrieved from NASA's ASRS site as of January 2009 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.