BUUAH, ich raste gleich aus. Ich mach nicht weiter, bis ich das Problem gefunden habe. Also nochmal ein paar News und einen auskommtierten Code.
Es geht jetzt doch bei keinem Flugzeug, auch nicht bei 2. Es hat wohl durch irgendeinen Zufall mal der Winkel gestimmt.
Code:
#define PROP_X (screen_size.x/1280)
#define PROP_Y (screen_size.y/1024)

void RadarMainLoop()
{
	int i; //Loop integer
	VECTOR draw; //The point, where the plane symbol should be drawn on the radar
	VECTOR drawoffset; //The Symbol of the plane is 16*16 pixel big. So the position has to be corrected.
	VECTOR temp; //Temporary vector
	while(ent_MyPlane==NULL) //As long my plane doesn't exists, wait
	{
		wait(1);
	}
	while(enet_ent_globpointer(ent_MyPlane)==ANET_ERROR) //As long my plane isn't a global plane
	{
		wait(30);
	}
	wait(-1); //Wait for other planes
	for(i=0;i<20;i++) //20 loops
	{
		if(ent_Plane[i]!=NULL) //Tests all Planes if they are aviable and if they are aviable, create a panel and a bmap for the symbol
		{
			if(enet_ent_globpointer(ent_Plane[i])!=ANET_ERROR) //Check again
			{
				radarplanepan[i]=pan_create(NULL,51); //Create panel for symbol
				radarplanepan[i].bmap=img_hud_radarplane; //Create the image for the symbol
			}
		}
	}
	while(s_radar_active==TRUE) //As long the radar is active
	{
		for(i=0;i<20;i++) //Loop threw all aviable planes and update their position on the radar
		{
			if(ent_Plane[i]!=NULL) //Check if the Plane REALLY exists, else it would crash
			{
				if(((abs(ent_Plane[i].x)-abs(ent_MyPlane.x))+(abs(ent_Plane[i].y)-abs(ent_MyPlane.y)))<=5000 && enet_ent_globpointer(ent_Plane[i])!=ANET_ERROR && ent_Plane[i]!=ent_MyPlane)
				//^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
				//If the distance to the plane and my plane is smaller than 5000 quants and the plane really exists,
				//draw the plane on the radar.
				{
					draw.x=ent_MyPlane.x-ent_Plane[i].x;//The difference of the x position of my plane and the other one
					draw.x=draw.x/39.0625; //Make it proportional to the screen and radar.
					//The radar has a radius of 128, that means 5000/128=39.0625
					draw.y=ent_MyPlane.y-ent_Plane[i].y;
					draw.y=draw.y/39.0625;
					draw.z=0;//We don't need the Z value, it's on the screen
					vec_set(drawoffset,vector(8,8,0)); //Set the offset because the symbol is 16*16 pixel big and the draw position would be on the top left corner. It should be in the middel of the symbol.
					vec_rotate(drawoffset,camera.pan); //Rotate the offset with the camera. The radar is rotating with the plane
					vec_rotate(draw,camera.pan+180); //Rotate the draw position with the camera. The radar is rotating with the plane
					draw.x+=(896-drawoffset.x*PROP_X)*PROP_X; //Add the radar position, subtract the offset and make it proportional to the screen resolution
					draw.y+=(640-drawoffset.y*PROP_Y)*PROP_Y; //Same here
					radarplanepan[i].pos_x=draw.x; //Set the panel position to the draw position
					radarplanepan[i].pos_y=draw.y; //Same
					radarplanepan[i].angle=ent_Plane[i].pan; //Set the angle of the panel to the in which direction the plane is looking at
					set(radarplanepan[i],SHOW); //Show the symbol
				}
				else //If the plane is toofar away or whatever
				{
					reset(radarplanepan[i],SHOW);	//Hide the symbol
				}
			}
		}
		wait(1); //Would freeze the engine
	}
}


I hope somebody can help me. Or should I move it to unanswered questions?