Narrative:

During our initial descent to [the airport] on the arrival we encountered severe; borderline extreme turbulence. During our descent from FL240 we encountered light to moderate turbulence. We illuminated the seat belt sign. Shortly thereafter the turbulence went from moderate to severe. The auto pilot; auto throttles; yaw dampener and pitch trim all disconnected. I was unable to maintain altitude; airspeed or directional control. We heard an airliner in our area experiencing the same turbulence and they [had advised ATC]. The airspeed quickly approached the barber pole; throttles were at idle. I instructed [the first officer] to extend the speed brakes fully as I was not able to take my hand off the yoke to manipulate the speed brakes myself. As the turbulence continued and became borderline extreme; I instructed [the first officer] to [identify ourselves as an emergency aircraft] as I was not certain what altitude we would end up at. At approx. FL210-FL200 we regained control of the aircraft and continued our descent to FL170 as an emergency aircraft. At FL170 we regained full control of the aircraft and were able to re-engage the auto pilot and auto throttles. At this point we advised ATC we would need no further assistance. There was no apparent damage in the cabin; although the cabin host went airborne 3 times before managing to strap herself in on the [crew seat]. She struck the ceiling at least once and mentioned some minor discomfort after landing. We had one passenger traveling with a support animal (10 lb cat). The passenger had been instructed on boarding that the cat would have to be kept in its pet carrier and the carrier to be at all times secured with a seat belt. The cat was out of the carrier laying on the seat besides the passenger and went airborne. The cat did not seem to suffer any injuries.on landing I called maintenance control and advised them of what had happened. I was told to write it up and submit it to maintenance control so they could schedule a structural inspection of the aircraft.

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Original NASA ASRS Text

Title: Gulfstream Captain reported moderate to extreme turbulence while descending with a momentary loss of control.

Narrative: During our initial descent to [the airport] on the arrival we encountered severe; borderline extreme turbulence. During our descent from FL240 we encountered light to moderate turbulence. We illuminated the seat belt sign. Shortly thereafter the turbulence went from moderate to severe. The auto pilot; auto throttles; yaw dampener and pitch trim all disconnected. I was unable to maintain altitude; airspeed or directional control. We heard an airliner in our area experiencing the same turbulence and they [had advised ATC]. The airspeed quickly approached the barber pole; throttles were at idle. I instructed [the first officer] to extend the speed brakes fully as I was not able to take my hand off the yoke to manipulate the speed brakes myself. As the turbulence continued and became borderline extreme; I instructed [the first officer] to [identify ourselves as an emergency aircraft] as I was not certain what altitude we would end up at. At approx. FL210-FL200 we regained control of the aircraft and continued our descent to FL170 as an emergency aircraft. At FL170 we regained full control of the aircraft and were able to re-engage the auto pilot and auto throttles. At this point we advised ATC we would need no further assistance. There was no apparent damage in the cabin; although the Cabin Host went airborne 3 times before managing to strap herself in on the [crew seat]. She struck the ceiling at least once and mentioned some minor discomfort after landing. We had one passenger traveling with a support animal (10 lb Cat). The passenger had been instructed on boarding that the cat would have to be kept in its pet carrier and the carrier to be at all times secured with a seat belt. The cat was out of the carrier laying on the seat besides the passenger and went airborne. The cat did not seem to suffer any injuries.On landing I called Maintenance control and advised them of what had happened. I was told to write it up and submit it to Maintenance Control so they could schedule a structural inspection of the aircraft.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.