In every French aiport, radio-equipements used by aircraft for instrumental approaches needs to be checked every year (and even more often in some cases).
One of the steps in the process is called in-flight calibration and is done by an ATR42 which is full of sensors (the kind of airplane where you should not use your phone ! 😛 ).
Here are some pictures in Cannes Mandelieu LFMD :
More information :