shanx
No.I dont believe you are in danger.(unless you are quite close) Modern wxr is relatively low power approx 100 watts I recall BUT the antennae are very directional which in short means that 100 watts ( for example) is effectively multiplied many times as its basically all in the one direction.
Output power is usually measured with an imaginary perfectly omni directional antenna called an isotropic radiator.
When that 100 w is fed into a modern plate (or any other directinal antenna) we use ERP or effective radiated power.
So you have a concentrated beam but it is very directional so if you are spotting you are still some distance away and as the plate scans you are not in the beam for extended periods.
With the inverse square law the power diminishes fairly quickly too.
I would say you are more at risk with the more powerful land based radars in operation around the fields.
I would think that minimising exposure to any high energy RF field is a good idea.More so the high end frequencies such as DME/ATC/TCAS then up to Rad Alt and then WXR which is a much shorter wavelength still.
They are not anywhere near the very short hi energy x ray band that can act at a cellular level. The jury is still out on what and how much damage is done but surely the less the better.
In answer to the one of the original questions it depends on the wxr used.ifyou are flying an old 727 or f28 for example you could be transmitting many thousands of watts thru someone. Not good.
"safe" distances on modern a/c are a matter of meters only but why take the risk.use it when you are clear of people and lining up would be sensible.You wont get a clear shot of anything until you clear the terminal and other reflective material anyway.
In the end vendor/company policy dictates but minimising exposure I think is wise.