Weather radar for adverse conditions such as fog, and night vision goggles are among the equipment fitted.
BBC: Wales air ambulance trials night rescues
Free-space optics would have the odd drawback, such as flocks of birds, showers of snowflakes or banks of fog interrupting the beams.
ECONOMIST: Optical communications
Horrified onlookers watched as the helicopter hit the crane amid low cloud and fog near Vauxhall station, south of the river and not far from landmarks such as the London Eye and the Houses of Parliament, and came plunging to the ground.
CNN: London helicopter crash prompts safety questions
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