A helicopter crash in which five family members from Milton Keynes were killed happened after the pilot failed to turn around when entering low cloud, accident investigators said.
The Air Accidents Investigation Branch (AAIB) found that the pilot "had the option to turn back, divert or land" when he entered an area of poor visibility.
The privately owned Twin Squirrel aircraft struck the side of Rhinog Fawr Mountain at an altitude of 2,000 feet.
A system which alerts pilots when they are approaching high terrain is available for the GPS equipment used by the helicopter, but it was not fitted
The bodies of the victims were found with the wreckage near Trawsfynydd in North Wales.