the in built immobilizing system the heel pieces 104 are kept in the engaged position that is to say in the position in which they project laterally from the rail 101 by the end 121 of the rod 120 the trigger 130 is in the corresponding stable position fig4 illustrates the guide system 101 in the case of simple opening of the external panel 40 without its removal in this configuration the heel pieces 104 are still in the engaged position and the slide 102 has slid toward the first end 103 of the rail 101 until possibly it has come into abutment against the return 105 of the heel pieces 104 fig5 to 8 illustrate the steps involved in completely removing and possibly replacing the external panel 40 to do this the trigger 130 is pivoted by hand or through an electric control into its second stable position it will be noted that the locking means are located at one end of the rail while the control means are located at the second end this is because such positioning is advantageous because it allows ease of access to the control means the moving cowl 40 beginning to open from the side at which the control means are located as this happens the link 132 transmits this movement to the rod 120 which undergoes a slight translational movement until the frustoconical end 121 has moved away from the heel pieces 104 to allow them under the effect of the spring 106 to return to their disengaged position thus the returns 105 of the heel pieces 104 no longer project laterally from the rail 101 and the slide 102 is free to continue its travel as illustrated in fig6 so that the rail 101 and the slide.