Square Leg. With modern radars there is no problem with using the radar when on the ground lined up regardless of an aircraft in front of you. Page 93 of the Pilots' Guide for Collins WXR 700X Weather Radar System states: "There is no apparent reason for restricting ground use - however it would be prudent to turn off the weather radar at the gate (Off, Standby or Test) and enable the weather radar after leaving the gate.