Prior to making an alignment check, it is necessary to level the aircraft both laterally and longitudinally. This may be accomplished by using the transit, spirit level, or plumb bob and datum plate method. You should always use the method of leveling specified by the manufacturer.

When you are leveling an aircraft for an alignment check, the aircraft should be inside a hangar where air currents will not interfere with the accuracy of the alignment readings. Jacks should be used to control the attitude of the aircraft during the check.

Figure 9-43.Transit leveling.

The transit method is the most accurate. Transit leveling is accomplished by sighting specified points on the aircraft. Two longitudinal and two lateral points are used for this method. The reference points are sighted through a surveyors transit. Figure 9-43 illustrates longitudinal and lateral leveling of an aircraft using the transit method.

Spirit Level 

Aircraft that use the spirit level method have leveling lugs either built into the structure or provisions for mounting them on the structure. The leveling lugs are usually in the nosewheel well. Spirit leveling lugs are shown in figure 9-44.

NOTE: The leveling lugs should be inspected for possible damage or misalign-ment prior to leveling the aircraft. In the event of damage to the leveling lugs, the repaired lugs must be calibrated by cross-reference with the transit leveling method.