http://www.ntsb.gov/Dockets/Aviation...076/403798.pdf
The following rules apply to the operation of aircraft radar equipment
while on the ground. In this context, "operation" means transmitting in
the "WX, TRB, TERR", position and does not include STBY, TEST, etc.
(1) Aircraft radar equipment shall not be operated while the aircraft is
being refueled.
(2) Aircraft radar equipment shall not be operated when another
aircraft, fuel truck, or other fueling equipment is within 50 feet
ahead or to either side of the nose.
(3) Aircraft radar equipment shall not be operated "nose on" to
another aircraft.
Note: Modem aircraft weather radar units typically transmit
about 70-80 watts of RF energy versus 50,000-75,000 watts
on older radars. The radar units in our aircraft fleet are
modern units, they do not pose a risk to humans, and they
comply with FAA Advisory Circular 20-68B. However,
despite safety to humans, it is prudent to comply with the
above restrictions to prevent possible damage to aircraft
equipment.