UFC 3-260-03
15 Apr 01
CHAPTER 8
REPORTING ALLOWABLE WEIGHT BEARING USING THE ACN/PCN PROCEDURE
1.
GENERAL DESCRIPTION.
a. The PCN is an index number representing the largest load on an established standard single
wheel which could be permitted to use a particular pavement without special reservations. Likewise, the
ACN is an index number representing the load on the same established standard single wheel that is
equivalent to an actual aircraft at a particular weight. The ACN therefore represents the equivalent loading
an aircraft will apply to a pavement, and PCN represents the equivalent loading a pavement can with-
stand. A comparison of these two values will indicate whether or not an airfield pavement can support a
particular aircraft.
b. Reasonably unique relations have been developed between ACN or PCN and aircraft weight for
any aircraft for limited ranges of subgrade strength and for pavement types. The ACN/PCN method
establishes four subgrade strength categories for each of two pavement types--flexible and rigid where
rigid includes plain concrete, plain concrete overlays, and nonrigid overlays on plain concrete. Any indi-
vidual pavement will have characteristics which place the pavement in only one of the subgrade and pave-
ment type categories.
c. The establishment of a PCN for a particular pavement will require relations between PCN and
aircraft weight for pertinent use aircraft and for the applicable pavement type and subgrade strength cate-
gory. These have been determined using established procedures and standard parameters of the
ACN/PCN method and are shown in figures 8-1 through 8-11.
d. Determination of the PCN for reporting weight-bearing capacities of pavements proceeds from
the results of the pavement evaluation. The Army, Navy, and Marine Corps evaluations should determine
the maximum allowable gross weight of the most critical aircraft that can use the pavement for the number
of equivalent passes expected to be applied for the following 20-year period (10-year period for Navy and
Marine Corps). The Air Force evaluation should determine the maximum allowable gross weight for
50,000 passes of the Group 10 (C-17) aircraft. The use of these maximum weights with figures 8-1
through 8-11 will allow the determination of the numerical PCN value. The evaluation should also provide
sufficient information to permit selection of the pavement type and subgrade strength category.
2.
PCN DETERMINATION.
a. To proceed with PCN determination, it is first necessary to establish the pavement type and sub
grade strength category. The pavement type is selected as either rigid (Code R) or flexible (Code F). If
the pavement is PCC or has PCC as a primary structural element, and is neither 102 millimeters
(4 inches) or less in thickness or completely shattered, it should be considered a rigid pavement. Virtually
all other pavement should be considered flexible.
b. Subgrade strength category should be determined from the following tabulation using character-
istics of the pavement being rated.
8-1
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