Page 241 - Aeronautical Engineer Data Book

196 Aeronautical Engineer’s Data Book
remainder in air-freight containers. In devel­
oped countries, freight is moved by mobile
mechanical equipment such as stackers, tugs,
and forklift trucks. At high-volume facilities, a
mixture of mobile equipment and complex fixed
stacking and movement systems must be used.
Fixed systems are known as transfer vehicles
(TVs) and elevating transfer vehicles (ETVs).
An area of high business growth is specialized
movement by courier companies which offer
door-to-door delivery of small packages at
premium rates. Cargo terminals for the small-
package business are designed and constructed
separately from conventional air-cargo termi­
nals – they operate in a different manner, with
all packages being cleared on an overnight basis.

11.2 Runway pavements
Modern airport runway lengths are fairly
static owing to the predictable take-off run
requirements of current turbofan civil aircraft.
All but the smallest airports require
pavements for runways, taxiways, aprons and
maintenance areas. Table 11.3 shows basic
pavement requirements and Figure 11.23 the
two common types.

Table 11.3 Runway pavements – basic requirements
• Ability to bear aircraft weight without failure
• Smooth and stable surface
• Free from dust and loose particles
• Ability to dissipate runway loading without causing
subgrade/subsoil failure
• Ability to prevent weakening of the subsoil by rainfall
and frost intrusion
The two main types of pavement are:
• Rigid pavements: Cement slabs over a granular sub­
base or sub-grade. Load is transmitted mainly by the
distortion of the cement slabs.
• Flexible pavements: Asphalt or bitumous concrete
layers overlying granular material over a prepared sub-
grade. Runway load is spread throughout the depth of
the concrete layers, dissipating sufficiently so the
underlying subsoil is not overloaded.