Narrative:

Aircraft experienced multiple altitude deviations while between FL430 - FL450 during the afternoon along the [ar routes] to ilm. The expected turbulence was briefed during the pre-flight between pilot flying (PF) and pilot monitoring (pm); but determined not to be severe enough to cancel the trip or re-route (re-routing to the west was impossible due to the frontal activity). An approaching cold front produced significant high altitude clear air turbulence (CAT) which we experienced initially northbound [from florida to the northeast]. We experienced continuous light to moderate CAT at FL450 abeam jacksonville; which increased in duration and intensity all the way up to the arrival and approach. On the northbound leg; the altitude deviations were 100-200 feet up and down at FL450 with very significant turbulence. On the return southbound leg; we encountered continuous moderate turbulence as soon as we leveled FL430. It was worse than the northbound experience. Upon handoff to washington center; we encountered the worst turbulence of the day; with the vertical trend magenta profile indicating +/- 4;000 FPM rates momentarily. During the handoff from frequency the aircraft encountered turbulence worse than moderate; and the aircraft began to climb. PF used the touch control steering (tcs) function to attempt to level off and reduce the climb rate; but without effect. Finally PF pushed very forcefully as aircraft passed FL433; still climbing - again with no effect. He pushed the nose to -2 degrees below the horizon without any effect whatsoever on the climb rate. As the aircraft approached (but did not reach) FL435; the trend reversed and PF was able to tcs the aircraft back to FL430 level with some difficulty due to the turbulence. Pm immediately advised washington center of the turbulence-induced deviation; controller advised 'no problem; there is nobody above you' and we reported level flight at FL430. Once we switched frequencies; we again experienced an uncontrolled ascent that reached FL434; stabilized; and PF returned aircraft to FL430. Pm advised controller who also stated that nobody was above us. Numerous other aircraft reported extremely poor ride conditions that day. Flight conditions were: FL430 wind: 276T/59; temp: -67; TAS: 448 (mach fluctuated between .78 -.84 due to windshear effect during the excursions. Planned mach was .80 as programmed in the FMS and flown with autothrottles engaged. Pm is submitting this NASA report for the altitude deviations that occurred that the crew was unable to control without drastic control inputs. On both occasions; negative 'gs' were experienced due to the effort expended to try to return to the assigned flight level; but without success. Post-flight debrief between PF and pm revealed that both crewmembers felt that any more control input during the deviation phase could have resulted in an unsafe attitude/ upset scenario. PF and pm commented on the severity of the turbulence; intensity and duration. Further post-flight debrief revealed that both crewmembers felt they did everything within their power to maintain safety of flight. Both agreed that a NASA report was in order due to the deviation of approximately 400 feet from assigned flight level.

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Original NASA ASRS Text

Title: A corporate jet crew flying north and south along the Atlantic coast at FL430 and FL450 reported turbulence severe enough to consider that at time they lost control with rates of climb and descent 4;000 FPM.

Narrative: Aircraft experienced multiple altitude deviations while between FL430 - FL450 during the afternoon along the [AR routes] to ILM. The expected turbulence was briefed during the pre-flight between pilot flying (PF) and pilot monitoring (PM); but determined not to be severe enough to cancel the trip or re-route (re-routing to the west was impossible due to the frontal activity). An approaching cold front produced significant high altitude clear air turbulence (CAT) which we experienced initially northbound [from Florida to the northeast]. We experienced continuous light to moderate CAT at FL450 abeam Jacksonville; which increased in duration and intensity all the way up to the arrival and approach. On the northbound leg; the altitude deviations were 100-200 feet up and down at FL450 with very significant turbulence. On the return southbound leg; we encountered continuous moderate turbulence as soon as we leveled FL430. It was worse than the northbound experience. Upon handoff to Washington Center; we encountered the worst turbulence of the day; with the vertical trend magenta profile indicating +/- 4;000 FPM rates momentarily. During the handoff from frequency the aircraft encountered turbulence worse than moderate; and the aircraft began to climb. PF used the touch control steering (TCS) function to attempt to level off and reduce the climb rate; but without effect. Finally PF pushed very forcefully as aircraft passed FL433; still climbing - again with no effect. He pushed the nose to -2 degrees below the horizon without any effect whatsoever on the climb rate. As the aircraft approached (but did not reach) FL435; the trend reversed and PF was able to TCS the aircraft back to FL430 level with some difficulty due to the turbulence. PM immediately advised Washington Center of the turbulence-induced deviation; Controller advised 'no problem; there is nobody above you' and we reported level flight at FL430. Once we switched frequencies; we again experienced an uncontrolled ascent that reached FL434; stabilized; and PF returned aircraft to FL430. PM advised Controller who also stated that nobody was above us. Numerous other aircraft reported extremely poor ride conditions that day. Flight conditions were: FL430 Wind: 276T/59; Temp: -67; TAS: 448 (Mach fluctuated between .78 -.84 due to windshear effect during the excursions. Planned Mach was .80 as programmed in the FMS and flown with autothrottles engaged. PM is submitting this NASA report for the altitude deviations that occurred that the crew was unable to control without drastic control inputs. On both occasions; negative 'Gs' were experienced due to the effort expended to try to return to the assigned flight level; but without success. Post-flight debrief between PF and PM revealed that both crewmembers felt that any more control input during the deviation phase could have resulted in an unsafe attitude/ upset scenario. PF and PM commented on the severity of the turbulence; intensity and duration. Further post-flight debrief revealed that both crewmembers felt they did everything within their power to maintain safety of flight. Both agreed that a NASA report was in order due to the deviation of approximately 400 feet from assigned flight level.

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.