Toward a new ICAO Aircraft Classification Number (ACN) methodology

Abstract

The ACN/PCN method rests on the concept of a single-wheel load which has
been employed as a means to define the landing gear assembly-pavement interaction without
specifying pavement thickness as an ACN parameter. For flexible pavements, airplane
landing gear flotation requirements are determined by the California Bearing Ratio (CBR)
method for each standard subgrade support category. The CBR method uses a Boussinesq
solution for stresses-strains and displacements in a homogeneous, isotropic elastic half-space.
To standardize the ACN calculation, the ACN-PCN method specifies that ACN values be
determined at a frequency of 10,000 coverages. This is done by equating a fictitious pavement
thickness, given by a mathematical model for an aircraft gear assembly, to the pavement
thickness for a single wheel at a standard tire pressure of 1.25 MPa (181 psi). Since it is
generally well known and accepted that CBR method is outdated and no longer in use for
pavement design and analysis purpose, this paper proposes a new approach for equating a
pavement thickness which would be required by a given aircraft to the pavement thickness
required for a standard single wheel-load, by using the Multi Layers Linear Elastic Analysis
(ML²EA) procedure. For this first attempt, the paper does not intend to give full details on the
procedure but offers the basis of a new approach with its numerical implementation and
further work to be done for method refinement.