Robinson R44 Raven II, G-CEFR
During an approach to land the almost-new aircraft started to oscillate in pitch with vibration felt through the cyclic. The pilot was unable to reduce the oscillation or vibration using control inputs so he made an expedited run-on landing. The landing was successful with no major damage to the aircraft or injury to personnel. The vibration was caused by excessive fore and aft rocking of the main rotor gearbox. The manufacturer discovered that the rubber forward main rotor gearbox mounts on new aircraft had become softer than those manufactured in the past. The manufacturer has therefore started installing new stiffer mounts on their aircraft. The incident aircraft was retrofitted with these new mounts and the vibration problem disappeared. The manufacturer also determined that the mounts became stiffer with age as a result of flight loads and heating, which explained why older aircraft had not been affected by the problem.
Robinson R44 Raven II, G-CEFR 10-07.pdf (247.72 kb)
Date of occurrence: 16 December 2006