Date: 202111
Local time of day: 1201-1800
Location: ZZZ.ARTCC, US
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
Aircraft component: Engine Vibration Indication
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Human factors: Workload; Troubleshooting; Time Pressure
Second reporter function: Captain; Pilot Flying
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Diverted; Flight Crew Landed As Precaution; Flight Crew Landed in Emergency Condition
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: About and hour into the flight from ZZZ to ZZZ1 at FL240 a vibration started. We had been out of moderate icing for about 20 minutes when it started. The wings had very little ice on them if any. Thinking the vibration was possibly caused by ice on the props we advanced the prop from 850 RPM to 1020 RPM. This caused the vibration to get worse. After about a min of no change in the vibration we reduce the props back to 850. Talked about what the next step should be and if we wanted to continue to ZZZ1. We decided that with moderate turbulence being reported on the arrival into ZZZ1 and icing reported on the arrival it would be safer to divert to a closer airport. We asked ATC the weather at ZZZ2 and ZZZ3. At first we where going to divert to ZZZ2 but with more information we decided to divert to ZZZ3. The Captain had me fly the airplane as he called Dispatch; Maintenance and told the passengers and Flight Attendants. We had slowed down to about 200 kts. and that seemed to reduce the vibration. I started getting the airplane set up to land at ZZZ3. We continued to ZZZ3 and discussed how we would handle the changes of props rpm for landing. As we got closer to ZZZ3 and slowed for more for landing the vibration seemed to decrease and was completely gone before landing I think. On the descent to ZZZ3 we stayed in VFR conditions to stay out of possible ice. Before we landed at ZZZ3 and we were set up to land the Captain took a second to double check and asked us to reevaluate everything.Without knowing what caused the vibration I'm don't know what I would recommend. It just reaffirmed to me that working as crew helps keep the flight safe. I think the Captain did a great job with CRM.


Second narrative: While enroute from ZZZ to ZZZ1 the airplane developed an engine vibration about 1 hour into our flight. At the time we were over ZZZ2 at FL240 and we had about 30 minutes until reaching ZZZ1.It began as a low vibration that quickly built to a severe vibration. At first I suspected that it was just ice on the propeller. We had previously flown through an area of light to moderate icing which covered a distance of roughly 100nm. That was shortly after reaching cruise altitude on departure. The aircraft had no issue handling the ice and no anomalies were apparent during this time. Just prior to entering the icing conditions we had a malfunction with the yaw damper which caused the auto pilot to disengage. We ran the checklist and fixed the issue. I don't believe that this issue and the engine roughness are related. However; knowing that it might fail again it factored into my later decision to divert.We had been out of the icing conditions for approximately 20 to 30 minutes before the vibrations began. The propellers should have been clear of ice by this point. All ice protection equipment was on prior to entering the icing conditions and it remained on throughout the flight. The boots and ref speed switch were selected on at the appropriate time.Since I thought the vibration issue might be caused by ice on the propeller we increased the RPM to Max (1020RPM) and I ensured that the propeller de-ice was on. As the RPM increased the vibration became much worse. It could be felt throughout the entire aircraft at 1020 RPM and 850 RPM.We reduced power on the engines to try and see if it would have an effect. It did not. After about a minute I felt that the vibrations were too rough and not improving so I reduced the RPM to 900 which reduced the vibrations slightly. There was also a decrease of vibrations when the RPM was set back to 850. However it was still the same intensity that it was prior to increasing the RPM. It was still very rough and noticeable throughout the aircraft.Just as this was beginning ATC had issued a clearance to start a descent on the arrival. The weather in ZZZ1 was very poor with high winds and moderate turbulence. The arrival also probably would have put us back into icing conditions. With all of these factors I did not feel comfortable attempting to continue into ZZZ1. I didn't want to run the engines any harder than they needed to be ran. ZZZ2 and ZZZ3 were closer and the weather was better. It would still be fairly windy and somewhat turbulent but we could remain clear of icing. I considered going to ZZZ4 but since we could not determine the source of our problem I did not want to have to fly further then necessary. The FO (First Officer) and I were in agreement.We notified ATC of the issue and that we would likely need to divert to ZZZ2 or ZZZ3. I asked about the weather in ZZZ3 and ZZZ2 to help build a plan. I also [advised ATC] as a precaution in case the situation deteriorated.I then spoke to the Flight Attendants and asked them if they felt the vibrations. They did. I told them to put everything away and that we would be diverting. At the time I didn't have a clear picture in my head of what our plan was yet so I wasn't able to give them a full briefing at that time. However I was able to do so later. I just wanted them to put everything away and sit down. I then made a PA to the passengers that we were aware of the problem and that as a precaution we would most likely be diverting to ZZZ2 or ZZZ3 and that I would update them. I know that I said more than just that but it's all a bit of a blur and I can't recall exactly what was said.I gave control of the aircraft to the FO so that I could focus on speaking with dispatch and planning a diversion.I then spoke with Dispatch to give them a brief overview of our intentions and then Maintenance to discuss the problem with them. During this time the FO was able to get more information and was told that ZZZ2 just had an aircraft go misseddue to weather from a visual. At that point ZZZ3 sounded like our best option. I went back to Dispatch and let them know about what we knew and that ZZZ3 looked like the best option. They got me the weather and concurred. I also notified them that we [advised ATC].Also throughout this conversation the FO began setting up for an approach into ZZZ3. He had also done a number of very helpful tasks and handled communications with ATC that greatly reduced my workload and made it easier to focus on the other various tasks. I don't recall everything he did but he was very helpful.As I was finishing up with Dispatch the engine vibrations slowly decreased until the point where they were gone. We think the vibrations occurred over at least a 15 minute time frame from first appearance to when they disappeared. I told Dispatch that information and that we would still be diverting as a precaution. Also we told ATC the same info.I made another PA to the passengers explaining the situation and to also to reassure them. I also spoke to the Flight Attendants and gave them a more complete briefing to make sure we were all on the same page.I took the aircraft back over from the FO at this point.Then we setup; briefed and ran all of our checklists as appropriate. The diversion went as expected after that. The engine vibrations did not occur again and we flew the remainder without incident.On post flight we did notice that there was some ice (uniform in appearance) on the front of the #2 propeller spinner but the rest of the aircraft was clear.The previous [ground training] over a year ago had a very similar scenario as part of the event. That was very helpful in working though this problem since both myself and the FO had done it.


Synopsis: Air Carrier Pilots reported an increasing air frame vibration while in cruise flight after leaving an icing weather area and decided to divert to avoid more icing and land in better weather.