Citation Excel (C560XL)
Flight Crew Air Transport Pilot (ATP)
Distraction; Communication Breakdown; Situational Awareness
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Aircraft Aircraft Damaged; Flight Crew Returned To Departure Airport; Flight Crew Landed As Precaution
Human Factors
On initial climb we noticed an unusual rattling noise from the outside of the aircraft. We elected to make a precautionary landing at the departure airport; staying in the pattern and landing without incident. No emergency was declared and we remained on the CTAF frequency throughout the return for landing.  Upon inspection of the exterior of the aircraft; we found the person that had fueled the airplane securing the fuel cap and closing the fuel door. He must have seen us return and realizing he had not secured the cap after fueling and came to see about it as we taxied in. The cap had scuffed and chipped the paint on the fuselage and left some small dents and nicks on the leading edge and inboard root section of the wing. My FO and I both had failed to do a final walk around the aircraft before finally closing the passenger door for flight.I was at the aircraft for the fueling process; but I was inside the cabin when it was happening. I should have been standing by the fueling person to monitor his actions. That way I would have been able [to] confirm the fueling hose removed; the cap replaced; and the fuel door latched. Of course; I and my partner both should have obeyed company procedures and done one last look around the plane before closing the passenger door for the last time prior to engine start.
I came out to the flight line where I found the Captain already in the left seat with his headsets on; ready to go. We were parked last at the end of the front row on the ramp; and I observed the aircraft's condition and its surroundings as I approached the forward entrance door. I checked that the horizontal stab was in the correct position; I checked the covers remained off; and that the Nav light was illuminated as the APU was running. The nose gear chock had already been removed by the Captain; but I fully bent down at the knees to make sure all 3 wheels were free from obstructions. I walked back momentarily to the left wing leading edge to visually confirm the latches and key locks for the battery and cargo compartment were engaged. Then climbed aboard and secured the forward entry door behind me. I did not visually inspect the right side of the aircraft at that time; under the erroneous premise that the Captain had already completed the same and final task when he removed the chocks. (No line service personnel were available to marshall us out.) Having already completed a thorough preflight inspection of the aircraft earlier in addition to and completely separate from the Captain's own inspection (during which I personally removed and stowed all engine and pitot covers;) I did not believe at the time there had been any changes to the overall condition or state of the airplane. On initial climb-out we heard an unusual intermittent noise; and returned for landing. [I suggest] adding a sensor to the fuel door; such as those installed on the cargo door; which would illuminate the service door annunciator in the cockpit.
Cessna CL560 crew heard an unusual noise after take-off and returned to departure airport to find the fuel door unlatched.