During a flight from Iceland to the UK, it was likely that ice formed somewhere on the aileron control system causing a jam in roll control. The crew were still able to control the aircraft longitudinally and descended to FL200. A significant, joint, input by the crew on the controls released the jam and normal roll control was regained. The rest of the flight was completed without further incident.
The Boeing 767 has experienced previous occurrences of roll control jams due to ice formation. Several modifications and inspections have been mandated due to previous events, all of which had been completed as required on G-DHLS before this event.