Primary radar[1] is only mostly used in larger airports or military installations. Secondary radar like ADS-B[2] has become really popular and requires the tran

Primary radar[1] is only mostly used in larger airports or military installations. Secondary radar like ADS-B[2] has become really popular and requires the transponder on the plane to be on and working. If you switch that off, for a lot of people you do disappear. 1. https://en.wikipedia.org/wiki/Primary_radar https://en.wikipedia.org/wiki/Primary_radar 2. https://en.wikipedia.org/wiki/Automatic_dependent_surveillance_%E2%80%93_broadcast https://en.wikipedia.org/wiki/Automatic_dependent_surveillan...