The need for an alignment check after extensive
aircraft. In the event of damage to the leveling lugs, the
repaired lugs must be calibrated by cross-reference
damage is rather apparent; however, this is not
with the transit leveling method.
necessarily so in situations where the aircraft exceeds
the g design limit or where a hard landing has been
Plumb Bob and Datum Plate
experienced. The alignment check under these
conditions may expose damage that might otherwise
This method uses a datum plate or scale mounted
go unnoticed.
on the deck of a compartment. Provisions for hanging
the plumb bob are located directly above the datum
BALANCING CONTROL SURFACES
plate. The aircraft is level when the plumb bob pointer
is at 0 degrees on the datum plate. Figure 16-45 shows
Some flight control surfaces are balanced at the
the plumb bob and datum plate method of aircraft
time of manufacture by adding counterweights to the
leveling.
inside of the leading edge of the control surface. This
balance must be maintained (within certain tolerances)
ALIGNMENT CHECK
throughout the service life of the control surface
because flutter or dynamic oscillation of these surfaces
The alignment or symmetry check is made after the
in flight is not desirable. Balance tolerances are always
aircraft has been leveled. This check is made by
specified in the aircraft structural repair manual.
measuring the distance between certain points on the
aircraft. These points are selected because they are
ALIGNMENT LEVELING METHODS
relatively static and because their location will best
r e f l e c t a ny m i s a l i g n m e n t . M o s t m a n u fa c t u r e r s
Prior to making an alignment check, it is necessary
recommend that the measurements be taken directly
to level the aircraft both laterally and longitudinally.
from one specified point to another. Figures 16-46
This may be accomplished by using the transit, spirit
show typical alignment dimensions for an F/A-18
level, or plumb bob and datum plate method. You
aircraft.
should always use the method of leveling specified by
the manufacturer.
On other types of aircraft, drop points are provided
When you are leveling an aircraft for an alignment
at various locations for use in checking the alignment.
check, the aircraft should be inside a hangar where air
Plumb bobs are dropped from each of these points to
currents will not interfere with the accuracy of the
the reference plane (floor) so that the pattern for
alignment readings. Jacks should be used to control the
measurement may be described. When you are using
attitude of the aircraft during the check.
this method, the elevation check dimensions are
measured from the drop points to the reference plane;
Transit
in this case, the floor. The horizontal check dimensions
are measured from one point (described by the plumb
The transit method is the most accurate. Transit
bob), along the reference plane (floor), to another
leveling is accomplished by sighting specified points
on the aircraft. Two longitudinal and two lateral points
point.
are used for this method. The reference points are
If the alignment check measurements exceed the
sighted through a surveyor's transit. Figure 16-43
tolerances listed in the aircraft structural repair
illustrates longitudinal and lateral leveling of an
manual, the aircraft must be considered non-airworthy
aircraft using the transit method.
until a special disposition can be made by higher
authority.
Spirit Level
WING TWIST CHECK
Aircraft that use the spirit level method have
leveling lugs either built into the structure or
With the aircraft leveled and the wings folded, it
provisions for mounting them on the structure. The
is possible to check the wings for twist. One
leveling lugs are usually in the nosewheel well. Spirit
checkpoint is provided on each wing. Clinometer
leveling lugs are shown in figure 16-44.
readings taken at these points, when compared to the
NOTE: The leveling lugs should be inspected for
fuselage longitudinal clinometer readings, will
possible damage or misalignment prior to leveling the
enable you to determine the condition of each wing.
16-52
