The FSMP is a schedule for performing the maintenance actions
necessary to maintain structural integrity throughout the life of a fleet. In principle, the FSMP provides the Office
of Primary Responsibility (OPR) sufficient detail for the establishment of
budgetary, structural integrity and maintenance plans. The FSMP is initially based on design usage
and is updated whenever significant changes occur in the fleet environment/stress
histories. Such changes are detected
through the data of the Loads/Environment Spectra Survey (L/ESS) elements. To maintain the airworthiness of the
individual aircraft, the FSMP is keyed to the data generated under the
Individual Aircraft Tracking (IAT) element.
Figure 8.1.3 is a schematic from Berens, et
al.  depicting the relation between the damage tolerance analyses, the
operational data collection and analysis programs and FSMP.
Figure 8.1.3 Relation of FSMP to IAT and L/ESS Elements of ASIP
The FSMP should contain:
of the anticipated inspection, repair, and modification actions,
critical locations and the crack sizes that trigger the required maintenance
actions for individual airframes, and
data required for the procedures of the Air Force Technical Order System.
The critical locations and critical crack sizes are the key
items of the damage tolerance approach to structural integrity. Figure 8.1.4 is a
generic schematic for the process of determining inspection intervals for a
monitored location for three or more inspection cycles.
Figure 8.1.4 Schematic of Inspection Interval Determination
Inspections for safety are scheduled at one half of the flight
hours for an assumed initial crack to grow to critical in the anticipated
stress environment. For pristine
structure, the initial crack size, a0, is representative of
flaws that might be in a structural detail as a result of manufacturing (see
Section 18.104.22.168). After an inspection,
the initiating flaw size, aNDI, is the reliably detected
crack size of the NDI method for the location. See Section 3.1. The crack size
versus time curves are adjusted to account for variations in usage severity
that are experienced by individual airframes.
The FSMP is based initially on the design loads spectrum, but
as data is obtained from the L/ESS program a new operational baseline loads
spectrum is developed and the FSMP is updated to reflect the operational usage.
The IAT program, also based originally on the design loads
spectrum, is updated to reflect the L/ESS
data. This update may involve changes
in the IAT method but usually only includes changes in the crack growth
rate in terms of the usage parameters being recorded by the IAT program.
Figure 8.1.5 from Berens, et al.
 shows the time sequence relation of these Force Management
activities. The final activity is the
airplane maintenance and the accumulation of these records.
Figure 8.1.5 Sequence of Force Management Elements [Berens, et al., 1981]
The final FSM plan and all of the test results and analysis
conducted during the design, manufacture, and testing of the aircraft form the
final data package which is delivered to the Air Force. It substantiates the damage tolerance
characteristics of the structure and describes how it may be maintained during
the life of the aircraft.
A transition period normally occurs during which the contractor
trains the user in all stages of the L/ESS, IAT, and FSM plan. It is essential that the user assume the same
regard for the treatment of damage critical parts that was practiced during
manufacture. The damage tolerance
analysis is highly dependent on the size of
the initial quality flaw. Manufacture
processes and handling were watched so that quality was preserved. It is now the responsibility of the user to
handle the aircraft in the same manner.
Disregard for the structure could result in complete loss of all the
previous efforts and could invalidate all of the tracking efforts.
It is the responsibility of the Air Force user to obtain the
data from the L/ESS to be used in the baseline analysis update. Early collection of L/ESS data will lead to
the most accurate use of the IAT data.
Recognition of this operation as part of the fracture control plan
should aid in the proper conduct of the task.
Keeping the equipment in service and striving for the maximum amount of
data return will lead to the most accurate final results. (This is, in part, also dependent on a selection
of parameters that are easy to record.)
Recording equipment and transducers should have a high reliability and
be easy to use.