A trim manifold assembly is utilized to facilitate control of the control valve in a fire protection system. The pairs of emitter and detector elements define two lines at right angles to each other, and one of the pairs lies to one side of the line defined by the other of the pairs, such that the two pairs of emitter and detector elements form a T shape. The measured value is compared with similar measured values previously established in respect of healthy joints andor joints characterised by a pathology. Airborne operation is achieved by changing the angle of the relative wind to produce vertical lift force on the airfoil assembly. On the main surface opposite to the active region when viewed from the outer peripheral trench, a potential fixing region where the body layer is exposed is formed. The fastener is formed by an elastic annular element insertable into the vestibule in an elastically deformed state and then exerts a force on the cover pushing and firmly retaining it in the vestibule.