What is the world record speed attained in a helicopter?

Lynx - The World's Fastest Helicopter 20 Years On 11/08/2006 The 11th August marks the 20th anniversary of the Westland Lynx helicopter setting a new world helicopter speed record of 249.1 mph (400.87 kph). Although other attempts have been made, 20 years on Lynx retains the title as the world's fastest helicopter.