Our antenna almost certainly missed some helicopter travel into Davos, such as aircraft that did not have or turned off their transponders. And some aircraft only broadcast their unique identifier, making it impossible to determine their location more precisely than the range of our device. That range has shown to be up to 75 miles (120 km) for tracking airplanes at cruising altitude but is likely much shorter for helicopters because mountains block transmissions from lower-flying craft. Helicopters that broadcast their locations flew out of the range of our antenna when they around 6 miles (10 km) away from our antenna, which was about 3 miles (5 km) from the main helipad in Davos.

David Yanofsky reported from Los Angeles and Jason Karaian from Davos.

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