Press and hold the test button.  In the real aircraft the test button is a latching on/off button, not a momentary one.  The NGX test is a little off from the real thing.  In the sim the PWS test pattern shows with the radar deselected,in the airplane it does not.  We normally leave the radar in test when it's not in use.
 
Our test procedure is as follows:
 
- Check that the radar is in test, it should have been left that way by the previous crew
- Select WX on both display control panels, the test pattern should display on both NDs
- Deselect test and immediately reselect it, the radar will now go through the PWS test.  You should hear "monitor radar display" followed by "go around, windshear ahead" and the PWS pattern will display on the NDs.  If you terminate the test early you will hear "radar test terminated"
- Deselect WX on both display control panels, all test patterns should no longer be displayed.

 

Can the test still be done with engines running joe?

 

 

- Check that the radar is in test, it should have been left that way by the previous crew

 

Why leave it in test?

 

 

Can the test still be done with engines running joe?

 

The test pattern will certainly show, I don't know if the PWS test will as I have never tried it.  I don't see why it wouldn't work with the engines running.  We only test it once a day on the first flight.  I can tell you for a fact the test pattern will show in flight if you select WX while the test button is still selected in.

 

 

 

Why leave it in test?

 

Good question, and I don't have the answer.  It's how we are taught and everyone at my airline does it.  I would guess it is to protect the people working around the airplane on the ground.  Leaving it in test makes it a two-step process to make the radar transmit making it less likely to inadvertently turn it on.

Thanks for the response!