Embraer 170 air carrier crew reported a vibration throughout the aircraft during cruise flight. The crew diverted to an alternate airport and landed safely.
Synopsis
Embraer 170 air carrier crew reported a vibration throughout the aircraft during cruise flight. The crew diverted to an alternate airport and landed safely.
Narrative
ZZZ1-ZZZ2 ZZZ Diversion. Filed FL290; ended up requesting and eventually getting FL360 to get above a weather system about 30 minutes into the flight. Reviewed performance documents to ensure we were safe for our weight at FL360. About 10 minutes after being a FL360; a sudden vibration began to appear; felt throughout the whole plane but also predominantly through the yokes; my side was vibrating slightly more than the Captains. I think I first stated what's that vibration" a few moments after the vibration began. I selected EICAS full to see if it was an engine vibration; it wasn't; parameters were within margin. The Captain began to suspect that it was a buffet from the high altitude and speed. We were unsure. I believe we tried to slow; with no improvement. We requested FL340 with ZZZ Center; they told us to standby. After a few moments it appeared the vibrations had finally went away. We canceled the request. Got a frequency change and as we did the vibrations came back; we requested lower with the new Center controller. They had to coordinate. We tried slowing and increasing the speed. We began to notice a trend that when the aircraft pitched up the vibrations were much stronger. Notified Dispatch of a possible problem. Decent to FL340 with vibrations continuing / worsening as we leveled off. Captain made the decision fairly quickly; after the level off and few turns on to course from Center; to divert. Notified Dispatch. New frequency checked in and began diversion/ [priority handling request] to ATC. Captain notified flight attendants (FAs); they also felt the vibrations as well a passenger in first asked them about it. I notified passengers with something along the lines of "precautionary diversion due to abnormal vibrations." We continued descending. Began slowing around 15000. Vibrations last felt about 10;000. Where soon after Captain had turn off the Autopilot for the first time (partially due to RVSM compliance) since the issue began. Automatic Flight Control Systems (AFCS) Fault Cyan message appeared on short final. Landed and taxied to the gate."
Second reporter narrative
We climbed to FL360 to get on top of the clouds between the fixes ZZZZZ and ZZZZZ1. Everything was normal for a couple of minutes until we felt a vibration. At first I dismissed it was chop from the weather we were passing over. Then it became more pronounced. I wondered if we are getting an aerodynamic buffet. According to the performance manual; we should NOT be in that realm. We tried slowing down to a slower speed. Vibrations were constant until the airplane reached the new selected speed; when it reached that speed; it started vibrating more as the nose pitched up to compensate for the speed. We returned to the previous speed. We descended to FL340 to see if that would help; it didn't. We notified our Dispatcher and decided it is better to figure out what was happening on the ground. With no obvious malfunctions other than vibrations; we diverted to ZZZ. As we descended; the vibrations continued; we turned off the Autopilot at a lower altitude. The vibrations last for about 5 seconds before they stopped. Tried engaging the Autopilot again and no more vibrations. Automatic Fault Control Systems (AFCS) FAULT appeared on ECIAS after we landed. Then parked at the gate….Throughout this; no abnormal indications on any system.During event:The vibration was felt more in the First Officer's (FO's) yoke than the Captain's (Sourced to Captain).The vibrations were felt by flight attendants (FAs) and some passengers.The vibrations could be felt on floor of Flight Deck.Note:Even though mostly constant; vibration was more intense when airplane nose up happened. Also in turns. So we used half bank mode for turns in descent.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.