Narrative:

The flight was cleared via a random route to coast in over the yqx VOR. After passing 45 degrees west larger aircraft began to report turbulence. We immediately put in a request to climb to FL430. It took some time. At approximately 46 or 47 west longitude we entered an area of sustained moderate (severe?) turbulence. We tried multiple times to obtain a climb to FL450. While we were waiting for clearance; our aircraft entered an area of turbulence that caused the aircraft to enter a sine wave oscillation. At the bottom of one wave; the aircraft was accelerating through mach .83 with a considerable amount of forward trim on the autopilot; yaw damper; and pitch trim disconnected. I had been guarding the yoke but not touching it. In the 3 seconds it took to say 'what the heck and push the 3 buttons that control the yaw damper; pitch trim; and autopilot we had lost about 420 feet. We climbed back to our assigned altitude and received a clearance to FL450. There was no loss of separation with any aircraft nor were any passengers or crew injured. We had seated and stowed as soon as the pireps were noted. We made a PIREP to gander center after radar contact at 50 west. I personally; still have the most respect for jetstream winds. I think flight planners should try to avoid areas like this. I would have gladly routed around this area had I known. The lack of ability to get a clearance also contributed to this. The lack of coverage in gander and shanwick has always been a problem. Sadly; the tombstone mentality is alive and well!

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Original NASA ASRS Text

Title: GIV flight crew experienced moderate to severe turbulence during a North Atlantic crossing causing the autopilot to disengage. An altitude deviation occurred before the crew could return to FL430. A clearance was then received for FL450.

Narrative: The flight was cleared via a random route to coast in over the YQX VOR. After passing 45 degrees west larger aircraft began to report turbulence. We immediately put in a request to climb to FL430. It took some time. At approximately 46 or 47 west longitude we entered an area of sustained moderate (severe?) turbulence. We tried multiple times to obtain a climb to FL450. While we were waiting for clearance; our aircraft entered an area of turbulence that caused the aircraft to enter a sine wave oscillation. At the bottom of one wave; the aircraft was accelerating through Mach .83 with a considerable amount of forward trim on the autopilot; yaw damper; and pitch trim disconnected. I had been guarding the yoke but not touching it. In the 3 seconds it took to say 'what the heck and push the 3 buttons that control the yaw damper; pitch trim; and autopilot we had lost about 420 feet. We climbed back to our assigned altitude and received a clearance to FL450. There was no loss of separation with any aircraft nor were any passengers or crew injured. We had seated and stowed as soon as the PIREPs were noted. We made a PIREP to Gander Center after radar contact at 50 West. I personally; still have the most respect for jetstream winds. I think flight planners should try to avoid areas like this. I would have gladly routed around this area had I known. The lack of ability to get a clearance also contributed to this. The lack of coverage in Gander and Shanwick has always been a problem. Sadly; the tombstone mentality is alive and well!

Data retrieved from NASA's ASRS site as of April 2012 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.