Although the dihedral and incidence angle of conventional modern aircraft cannot be adjusted . They should be checked at specified periods and after heavy landings or abnormal flight loads to ensure that the components are not distorted and that the angle within permitted limits. The relevant figures together with permitted tolerances are specified in the appropriate manual for the aircraft concerned, but the actual figures relevant to an individual aircraft are recorded in the aircraft log book.

The usual method of checking rigging angles is by the use of special boards in which are incorporated or on which can be placed an instrument for determine the angle, that a spirit level or clinometer as appropriate. On a number of modern aircraft the rigging can be checked by means of sighting rods and a theodolite.

Verticality of Fin.

After the rigging of the tail planes has been checked, the verticality of the fin relative to a lateral datum can be checked from a given point on the either side of the top of the fin to a given point on the port and starboard tail planes respectively, the measurements should be similar within prescribed limits. When the verticality of the fin stern post has to be checked, it may be necessary to remove the rudder and drop a plumb bob through the rudder hinge attachment holes, when the cord should pass centrally through all holes. It should be noted that some aircraft have the fin offset to the longitudinal centerline to counteract engine torque.

Engine Mountings

Engines attached to the wings are usually mounted with the thrust line parallel to the horizontal longitudinal plane since, due to their disposition along the wing, the outboard engines are often offset a degree or so to enable the slipstream from the propellers to converge on the tail-plane. The check to ensure that the position of the engine, including the degree of offset, is correct depends largely on the type of the mounting, but usually entails a measurement from the centerline of the mounting to the longitudinal center line of the fuselage at a point specified in the relevant manual.