Date: 201712
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: IMC
Light: Daylight
Aircraft: Citation Excel (C560XL)
Operator: Corporate
Operating under: Part 91
Flight plan: IFR
Mission: Ferry / Re-Positioning
Flight phase: Climb
Airspace: Class E ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Reverser Lockout
Component problem: Improperly Operated
Reporter organization: Corporate
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness
Second reporter function: Captain; Pilot Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Diverted; Flight Crew Landed in Emergency Condition; General Maintenance Action
Contributing factors: Aircraft; Human Factors
Primary problem: Aircraft

Narrative: Maintenance deferred both thrust reversers. After being deiced with Type 1 fluid the crew departed. On climb out passing through approximately 13;000 ft and approximately 270 knots the aircraft developed an airframe vibration. There were no abnormal cockpit indications. As the crew continued to climb and accelerated the vibration seemed to get worse. Climbing through approximately FL260 the crew decide to return to FL240 and maintain a speed of 250 knots or less in case the vibration was caused by an issue with a gear door. The crew coordinated this with Center. The crew discussed the issue that at that airspeed and altitude the aircraft did not have the range to make [the destination] as originally planned.PIC contacted flight control and maintenance control via ARINC to inform them of the situation; enlist their help in determining the safest course of action; and determine what airport to use as an alternate. After analyzing the situation with all available resources; the crew determined it was safe to continue flight at a lower altitude and a speed lower than the landing gear extended limit speed (VLE) of 250 KIAS. The group determined that the best alternate airport for the situation was ZZZ. At this point the crew informed ATC of their plans to divert and [advised of a] possible landing gear or other door issue. Crash/Fire/Rescue services were requested as a precaution. Enroute to [the diversion airport]; SIC went into the cabin and looked out the windows to confirm that the flaps were retracted and the speed brakes were properly stowed. All visual indications showed the flaps up and speed brakes retracted. The descent and approach were normal and the landing was smooth and successful with no issues. After parking aircraft; the crew conducted a post flight inspection and found the bottom portion of the right thrust reverser had deployed approximately 1/2 inch on the inboard side. Crew believes this to be cause of vibration experienced. There were no Thrust Reverser or any other abnormal indications with the instruments or annunciators. Again; it should be noted the Thrust Reversers were deferred and placed on the MEL the previous night. This was the first flight after a maintenance event.


Second narrative: After departing during the climb out at approximately 13000 ft; the aircraft started an instantaneous vibration at approximately 270KIAS. Vibration was 'shallow' and comparable to an exterior gear door being open or a speed brake slightly deployed. There were no abnormal indications on the instruments or annunciators. At first I; the PIC; thought it may have been air turbulence and elected to continue the climb. As the aircraft continued climb through FL200; I noticed the vibration continued uniformly and increased intensity as airspeed increased. After passing thru FL260 crew informed ATC a request to descend to FL240 and keep a slower airspeed while crew worked a possible issue. Since there were no indications on the instruments; I could only assume a possible exterior door or other obstruction was causing an airflow issue. After analyzing the aircraft characteristics; the crew decided the airplane was still safe to continue flight but would keep the aircraft at a lower Flight Level and keep the speed below 250KIAS referencing a gear extension limitation. Vibration was also less when aircraft was below 250KIAS. PIC then contacted Flight Control and Maintenance Control via Arinc frequency and informed them of the issue. PIC informed maintenance control the aircraft did not have the fuel reserves to continue at the lower Flight Level and asked if there was a preferred alternate for maintenance. ZZZ airport was decided upon as a group and diversion was started. Crew then informed ATC of the diversion and possible 'gear or other door' issue and requested Fire Trucks upon arrival as a precaution. During cruise; SIC proceeded into the cabin to verify through the window that the flaps and speed brakes were stowed and not deployed. All visual indications showed normal stowed condition. WX at the time of initial diversion was showing 9 sm visibility and scattered to broken skies starting at 1500 ft AGL with winds favoring a crosswind landing. While enroute weather started to deteriorate and was approximately 2 sm visibility and blowing snow while we were executing the approach. Landing was smooth and successful with no incidents. After parking aircraft; crew conducted a post flight inspection and found the bottom portion of the right thrust reverser had deployed approximately 1/2 inch on the inboard side. Crew believes this to be cause of vibration experienced. Again there were no Thrust Reverser or other abnormal indications with the instruments or annunciators. It should be noted the Thrust Reversers were deferred and placed on MEL the previous night with circuit breakers collared. This was the first flight after the maintenance event.


Synopsis: C560XL flight crew reported significant vibrations during climb; seemingly from a partially deployed reverser; that required a diversion.