Page 233 - Planning and Design of Airports

198 Airp o r t D e sign

10 ft for every foot in elevation difference between the lowest point
and highest point on the runway.
At higher elevations, it is often the case that the required runway
length is greater for aircraft less than 12,500 lb MGTOW than for air-
craft greater than 12,500 lb. If this is the case, the design runway
length would be that for the lighter aircraft. As such, airport planners
estimating runway lengths at high elevation airports should perform
runway length estimations for the smallest aircraft, in addition to that
for the selected critical aircraft.

Aircraft Greater than 60,000 lb MGTOW
For aircraft greater than 60,000 lb MGTOW, runway lengths are esti-
mated based on the specific performance specifications of the critical
aircraft. These performance specifications may be found in the pub-
lished aircraft “airport planning manuals.” These manuals may be
found on the Internet sites of the major aircraft manufacturers.
Within the aircraft airport planning manuals are performance
charts that are used to determine the aircraft’s required runway lengths
for both takeoff and landing, based on the aircraft’s operating con-
figuration, its estimated weights during takeoff and landing, as well
as the airport elevation and average high temperature during the hottest
month.
Example Problem 6-2 illustrates the procedure for estimating runway
length using these charts.

Example Problem 6-2 Consider the situation where an airport with elevation
1000 ft AMSL and mean daily maximum temperature of the hottest month
of 84°F, is planning for a new runway to be designed for the Boeing 737-900
aircraft, equipped with Pratt & Whitney CFM56-7B27 engines. At the airport
a runway gradient of 20 ft is projected.
According to the performance specification chart, illustrated in Fig. 6-16,
found in the Boeing 737-900 airport planning manual, the maximum design
landing weight for the aircraft is 146,300 lb and the maximum design takeoff
weight is 174,200 lb.
First, estimation of required runway length for landing is performed using
the landing runway length performance chart for the aircraft. As with most
landing performance charts, runway length requirements found landing may
be found under both dry and wet runway conditions. For airport planning pur-
poses, design runway length for landing is estimated by considering wet runway
conditions. If a landing runway length performance chart does not include wet
runway conditions, the design runway length is estimated as the runway length
found under dry runway conditions, plus 15 percent.
Figure 6-17 illustrates this example. Applying the case example, a vertical
line is drawn from the base of the horizontal axis at the location of the maximum
design landing weight (146,300 lb), up to an interpolated point between the “sea
level” and “2000 ft” (to represent the example airport’s 1000 ft elevation) wet-
runway curves, and then a horizontal line is drawn to the vertical axis, where the
estimated required runway length may be found. In this example, the estimated
runway length for landing is approximately 6600 ft.