On 6 November 1986, a Boeing-Vertol Model 234LR Chinook helicopter returning workers from the Brent oilfield crashed on approach to land at Sumburgh Airport in the Shetland Islands. At 2.5 mi (4.0 km) from the runway the helicopter had a catastrophic forward transmission failure which caused the tandem rotor blades to collide. The helicopter crashed into the sea and sank. Forty-three passengers and two crew members were killed in the crash; one passenger and one crew member survived with injuries.