Citation Excel (C560XL)
Flight Crew Air Transport Pilot (ATP)
Confusion
Aircraft Equipment Problem Critical; Inflight Event / Encounter Other / Unknown
Flight Crew Returned To Departure Airport; General Flight Cancelled / Delayed; General Maintenance Action
Aircraft
The PIC was PF in the left seat; I was PNF (SIC) in the right seat. FAR 135 trip with two passengers ZZZ-ZZZ1. During initial climb the PF stated that while hand flying he noticed a vibration in the Control yoke; and asked me to place my hands on the Control yoke to verify. I also noticed a continuous vibration in the Control yoke. The vibration was not only in the upper control yoke; but also in the Control column and I could feel the vibration in the cockpit floor when I placed my feet near the base of the control column. There was no vibration in the rudder pedals. I advised ATC that we would like to level at 16;000 feet to troubleshoot an issue. We discussed further as a crew; and operated from 200 IAS to 280 IAS with no noticeable increase or decrease in the vibration. We also tried the autopilot on; off; and yaw damper off with no increase or decrease in the vibration. The PIC remained PF and took COM1 while I attempted to look up an Abnormal Checklist for flight control vibration. I found no such checklist. We decided that it would be ill advised to continue up to altitude on a two hour and 45-minute flight with this continuous vibration as we were unsure of its source. I contacted the Assistant Chief Pilot (ACP) via company Communications on my company IPhone. I advised him of the abnormality; and that we were planning a return to ZZZ. Once I was finished contacting the company; the PIC transferred aircraft control to me and asked me to get us headed back towards ZZZ. The PIC then advised the passengers of our issue and our return to ZZZ. I transferred aircraft control back to the PIC; and accomplished the short segment checklist and prepared for our return to ZZZ (we had not yet completed the After Takeoff Checklist as we were troubleshooting the control issue during climb). We determined that we were about 500lbs over landing weight; and we elected to burn fuel as to not land overweight. As we approached ZZZ; we advised ATC that we would like to delay a bit to burn fuel. ATC gave us 'box vectors' as they called it over ZZZZZ Intersection (ZZZZZ Intersection is the FAF on the RNAV XX approach to ZZZ). After we configured the aircraft for landing; there was no change to the control vibration and it continued until landing. Once we achieved landing weight; we returned for landing Runway at ZZZ; and landed uneventfully. The recovery aircraft was already available at ZZZ. We transferred the passengers and their baggage to the recovery aircraft and crew; and they departed immediately. A Maintenance Technician met us at the aircraft after returning to ZZZ; and we were able to give an in depth explanation of the issue to him directly. The aircraft was written up Aircraft On Ground (AOG).During interior and exterior pre-flight; we noticed no abnormalities with the Flight controls. The Aft Accessory Bay was inspected during preflight; during which we checked the flight control cables and noticed no abnormalities. During the After Start Checklist; we accomplished a Flight Control Check and noticed no abnormalities prior to taxi. In flight we had discussed the fact that the vibration affected the entire control column; including being felt in the floor. This would denote that it was not an issue with ailerons or rudder; and that the issue likely had something to do with the elevator or elevator trim tab. While I was on the phone with the ACP inflight; he mentioned the elevator trim tab or elevator as likely being the issue as well. With an unknown vibration; there was no way to know if the condition would improve or deteriorate at altitude over the course of a nearly three hour flight. I believe that we made the prudent decision to return for landing. We were methodical about aircraft control and procedures; and worked well together as a crew.
Reporter stated he was told Maintenance had replaced bearings; bolts; and nuts at the rudder to vertical stab attachments. Flight test of the aircraft for vibration found ailerons and elevators were within limits and no further vibrations noted after the rudder attachments were replaced. Reporter stated he would not have thought the rudder was the issue; especially since no vibration was felt in the pedals when he and the Captain experienced the inflight vibration in the control column; yoke; and cockpit floor.
First Officer reported experiencing continuous vibration in the control yoke; control column; and cockpit floor during initial climb in a CE560XLS aircraft. No vibration in the rudder pedals. No increase or decrease in vibration after cycling the autopilot on/off. The flight crew returned to the departure airport. Rudder bearings; bolts; and nuts were replaced.