Date: 201304
Local time of day: 0601-1200
Location: SCT.TRACON, CA
Flight conditions: VMC
Weather elements / visibility: Turbulence; 20
Light: Daylight
Aircraft: Citation Excel (C560XL)
Operator: Air Taxi
Operating under: Part 135
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class E ZLA
ATC / advisory: TRACON SCT
Reporter organization: Air Taxi
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human factors: Physiological - Other; Workload
Second reporter function: Captain; Pilot Flying
Anomaly: Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Loss Of Aircraft Control; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Regained Aircraft Control; General Maintenance Action
Contributing factors: Weather
Primary problem: Weather

Narrative: During a charter flight descending on the FERNANDO 5 arrival; weather was clear at our altitude; and while our destination did have a ceiling at the time; it was VFR. We were commenting on the current ATIS about the very low altimeter setting. If I remember correctly; it was 29.67. We were talking about how we should be in worse conditions then the continuous light turbulence we were experiencing. I was the pilot not flying sitting in the right seat for this leg of the trip. North West of Fillmore California near PIRUE Intersection; the aircraft entered an area of severe turbulence. The aircraft was in a descent nearing an assigned altitude of 11;000 FT at a speed of approximately 270 KTS on an assigned heading off the FERNANDO 5 arrival when sudden; intense downdrafts and updrafts disengaged the autopilot. The pilot flying's headset was flung off; inaccessible down in the foot well area. Airspeed was reduced; and we tried to maintain altitude; but descended to approximately 10;600 FT.I was able to communicate with ATC; to inform them of our situation; offering the reason for our first loss of 400 FT initial deviation from the assigned altitude. We called back to the passenger and he said he was OK; although looked shaken. As we leveled again at 11;000 FT; a second; violent and longer period of extreme turbulence was experienced. The aircraft was predominantly buffeted up and down more than side to side; but certainly a significant event. I had my iPad sitting on my right leg; but had not strapped it down yet since we were still above 10;000 FT. It flew past me and ended up behind the cockpit. My coffee cup flew out of the cup holder and ended up under my seat; and my sunglasses flew out of my shirt pocket and were found down by the left seat rudder pedals. I'm sure I hit my head on the sun visor; but don't remember it happening. I glanced back to check on our passenger and saw him now surrounded by many items normally stowed in seat pockets or some of the cabinets; papers; eyeglasses; pillows; etc. With the pilot flying's headset off; we shouted options not knowing if more extreme turbulence was still to come and we elected to request a turn toward the coast and lower altitude. We were given another heading toward the coastline and assigned 8;000 FT. ATC was very accommodating during this period; and gave us a block of airspace from 11;000 FT to 8;000 FT. Somewhere in this; I took the controls and the pilot flying was able to retrieve his headset. I then turned the aircraft back to him and we had ICS communications again. During this descent and for the duration of the flight; the aircraft was still in moderate to light turbulence. The turn to final and the landing at our destination was uneventful. We had Maintenance do a turbulence inspection on the aircraft before we flew it again; and no damage had been done. I guess Cessna builds strong airplanes! In reviewing our actions during the turbulence; I don't know if there was anything that we could have done differently. The low altimeter setting was a clue to us; but I underestimated the violence that was to follow. The pilot flying did a masterful job maintaining control of the aircraft under some very extreme circumstances.


Second narrative: [This report contains no additional information.]


Synopsis: A CE-560XL encountered severe turbulence at 11;000 FT while descending on the FERNANDO 5 Arrival into Southern California; but damage was not discovered during a post flight airframe inspection nor did any occupants sustain injury.