1e10 doesn’t not work too.
When I add the plane to the scene, does it automatically add its children?
It worked on an other scene. Is there any way to flip the axes with three.js of an object and/or move it to the extremities of the object for example ?
Try something in between. 
You may also want to check the bounding box of the airplane geometry to determine an appropriate scale.
When I add the plane to the scene, does it automatically add its children?
Yes.
I did and it still doesn’t show up. Maybe it is from my addObject() Methode because i tried it in an other scene and it works.
Would be awesome if there is an option to do so in three.js cause I will be working alot with coordinates afterwards.
It is not clear to me what you are asking. I take it you are talking about flipping the AxesHelper, or scaling it to match the size of the geometry? Is that right?
What coordinates?
This discussion clearly does not belong into this topic (sorry @Wazaa). But I have to clarify that the docs already mentioned this: three.js docs
Three.js uses intrinsic Tait-Bryan angles.
A quick updated. So It appears that the meshe was simply exported from a 3d modeler program with its origin in a weird position. So I’ve imported the meshe into blender and changed the origin axes to my convenience. So i t wasn’t the STLLoader problem but more the mesh that I used. Thank you everyone for your help.