The other Lynx helicopter was ahead in the valley range and it was necessary for the crew to locate it and maintain separation whilst descending. There was a loss of situational awareness with respect to height and rate of closure with the ground resulting in a misjudgement of height over the featureless desert surface
Necessary to locate it [other Lynx] in order to avoid a collision? What about installing CWS. According to a Mil Cap safety management report, dated 28th Jan 2014, 'Mid-air collision is Cdr JHC's (ODH) number one Air Safety risk', a risk that was known about at the time of the accident, and a risk that was not ALARP. This is what is said about the CWS in Bond's Super Puma helicopters. Bond did not wait for an accident, they realised there was a possibility and acted.
"There is no doubt that the TCAS II display rapidly becomes one of the more important instruments in the cockpit. The enhanced situational awareness provided by TCASII allows the pilots to concentrate on flying and operating the aircraft with higher levels of confidence and safety than would be possible with other systems"
DV