Section 8.0. Force Management and Sustainment Engineering
The maintenance of the damage tolerant capability of an
aircraft after it enters service is the function of an activity called Force
Management. Recommended guidance for accomplishing the force management objectives
is contained in Tasks IV and V of MIL-HDBK-1530. As this activity can be
considered to be the final phase of fracture control, a brief summary of the
major force management elements is presented in the following. See Berens, et
al.  for a more extensive earlier discussion of Force Management.
Structural maintenance activities of a fleet are initially
scheduled in accordance with the Force Structural Maintenance Plan (FSMP) of
Task IV. Timing of maintenance actions (inspections, repairs, modifications, or
retirement) is determined from predicted crack growth for the design
environmental/stress usage. Task V calls for the initial FSMP to be updated as
necessary to account for unexpected critical details and changes in usage.
However, the effects of usage and time can
eventually produce a degree of widespread cracking and corrosion that are not
accounted for in the FSMP. Because
of the uncertain nature of the sizes of cracks that might be in the fleet and
the need to evaluate the interactive effects of cracks in multiple elements,
the FSMP assessments of the effect of potential cracks at a single
location can become inadequate. When the aircraft of a fleet are experiencing widespread fatigue cracking or corrosion, are
being used beyond the original life goals, or have been repaired, a
change in the initial approach to maintenance planning is required. The fleet
is then said to be aging according to MIL-HDBK-1530. Structural integrity is
maintained in an aging fleet through a process known as sustainment.
Sustainment encompasses the actual structural maintenance as well as the
analyses and tests needed to plan the maintenance tasks.
The ASIP force management concept is to monitor the usage of
each aircraft and compare the computed damage accumulation, as described by a
crack growth analysis, with the predicted damage accumulation of a baseline
usage aircraft. The maintenance schedule of the monitored aircraft is modified
as necessary to account for differences of usage from the baseline. This section discusses the major elements of force
management. Since the force management techniques for sustainment
analysis are still being developed, a general discussion of the damage
tolerance sustainment issues is also presented.