Narrative:

We were positioning the aircraft (w/o passengers) to our home base and attempted to cross a line of thunderstorms approximately 300 miles from our destination. We had climbed to FL490 but as we approached the final part of the line it was evident that we would enter the cloud tops unless we climbed higher (FL510 is aircraft ceiling). We received a clearance to climb but started to enter the tops at nearly the same time. Engine anti-ice heat was selected 'on' with a corresponding loss of climb performance and downdrafts encountered nearly simultaneously. Significant turbulence and precipitation began to occur and our climb turned into a descent over which we had no control as in order to maintain adequate airspeed we had to descend. [We] were unable to advise ATC immediately due to other radio traffic. We were able to arrest the descent and maintain FL450 with anti-ice heat 'on' and eventually advise ATC of the need for a revised clearance to maintain FL450. The controller promptly cleared us to maintain FL450 and we passed on the turbulence/precipitation report. No other communication was exchanged with ATC except for the next routine frequency change.the weather encounter was avoidable and solely my responsibility as I should have requested a lateral deviation and/or altitude change much sooner. A weather cell to our left was 'painting red' and the one to the right was 'yellow'. I did not anticipate the degree of turbulence/precipitation we encountered because I thought we had adequate horizontal and vertical clearance from the cells. Obviously; I was not taking into account the vertical development already seen. A contributing factor may have been my past experience of successfully 'topping' similar lines of weather; but not at this altitude. I should have realized the fact that there was not sufficient margin to attempt this. After landing we advised our 'maintenance crew' of the turbulence/precipitation encounter and asked that appropriate inspections be completed. Some 'static electricity' protection elements on the airframe needed to be replaced but there was no evidence of a lightning strike or turbulence damage (the autopilot was; fortunately; in the 'pitch mode' rather than altitude hold or some other vertical mode during the turbulence encounter and remained engaged during the descent). Two other potential contributing factors may be that I was feeling tired on this leg (only 9 hours of duty at this point) and that we had no passengers on board. I have evaluated my decision making process as a result of this event and will continue to work on improving it.

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Original NASA ASRS Text

Title: CE-750 Captain reported descending without a clearance to maintain airspeed while trying to go over the top of a line of thunderstorms.

Narrative: We were positioning the aircraft (w/o passengers) to our home base and attempted to cross a line of thunderstorms approximately 300 miles from our destination. We had climbed to FL490 but as we approached the final part of the line it was evident that we would enter the cloud tops unless we climbed higher (FL510 is aircraft ceiling). We received a clearance to climb but started to enter the tops at nearly the same time. Engine anti-ice heat was selected 'on' with a corresponding loss of climb performance and downdrafts encountered nearly simultaneously. Significant turbulence and precipitation began to occur and our climb turned into a descent over which we had no control as in order to maintain adequate airspeed we had to descend. [We] were unable to advise ATC immediately due to other radio traffic. We were able to arrest the descent and maintain FL450 with anti-ice heat 'on' and eventually advise ATC of the need for a revised clearance to maintain FL450. The controller promptly cleared us to maintain FL450 and we passed on the turbulence/precipitation report. No other communication was exchanged with ATC except for the next routine frequency change.The weather encounter was avoidable and solely my responsibility as I should have requested a lateral deviation and/or altitude change much sooner. A weather cell to our left was 'painting red' and the one to the right was 'yellow'. I did not anticipate the degree of turbulence/precipitation we encountered because I thought we had adequate horizontal and vertical clearance from the cells. Obviously; I was not taking into account the vertical development already seen. A contributing factor may have been my past experience of successfully 'topping' similar lines of weather; but not at this altitude. I should have realized the fact that there was not sufficient margin to attempt this. After landing we advised our 'maintenance crew' of the turbulence/precipitation encounter and asked that appropriate inspections be completed. Some 'static electricity' protection elements on the airframe needed to be replaced but there was no evidence of a lightning strike or turbulence damage (the autopilot was; fortunately; in the 'pitch mode' rather than altitude hold or some other vertical mode during the turbulence encounter and remained engaged during the descent). Two other potential contributing factors may be that I was feeling tired on this leg (only 9 hours of duty at this point) and that we had no passengers on board. I have evaluated my decision making process as a result of this event and will continue to work on improving it.

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.