Thanks everyone for your answers. I've well measured something opened on the 5mm jack connector. So maybe it's the mic.
So it seems that :
6.35mm jack is for headset and is about 60 ohms
5mm jack is for mic and acts like an open circuit.
Does anybody with that kind of aircraft headset could confirm that the mic is well on 5mm jack and headset is 6.35mm jack?
If yes I guess that kind of headset could work. I'll give it a try.