Page 283 - Planning and Design of Airports

244 Airp o r t D e sign

off on to the taxiway and clear the runway. For the first component it
can be assumed that the touchdown speed is 5 to 8 kn less than the
speed over the threshold. The rate of deceleration in the air is about
2
2.5 ft/s . The second component is about 3 s and the third component
depends upon exit speed. Time to turnoff from the runway will be on
the order of 10 s. Thus the total occupancy time in seconds can be
approximated by Eq. (6-8).
V − V V − V
R = ot td ++ td e + t (6-8)
3
i a 2 a 2
1 2
where R = runway occupancy time, s
i
V = over the threshold speed, ft/s
ot
V = touchdown speed, ft/s
td
V = exit speed, ft/s
e
t = time to turnoff from the runway after exit speed is reached, s
a = average rate of deceleration in the air, ft/s 2
1
a = average rate of deceleration on the ground, ft/s 2
2
During the runway capacity studies cited earlier [18] data were
also collected on runway occupancy time. These data, which are tab-
ulated in Table 6-27, indicate the total runway occupancy time of each
class of aircraft which have exited the runway at exits located at vari-
ous distances from the arrival threshold. As may be observed in this
table, typical runway occupancy times for 60 mi/h high-speed exits
are 35 to 45 s. The corresponding time for a 15 mi/h regular exit is 45
to 60 s for air carrier aircraft.

Design of Taxiway Curves and Intersections
The basic design of taxiway curves and intersections for three of the
most common types of taxiway intersections have been developed by
the FAA [6]. These designs have been taken from this reference and
were shown in Fig. 6-35. The dimensions recommended by the FAA
for the taxiway width, centerline radius, fillet radius (inner edge
radius), and the length of the fillet lead-in are given in Table 6-23. The
dimensions given for the fillet radius in this table are related to the
taxiway centerline radius.
When an aircraft negotiates a turn with the nose wheel tracking a
predetermined curved path, such as a taxiway centerline, the mid-
point of the main undercarriage does not follow the same path of the
nose gear because of the fairly large distance from the nose gear to the
main undercarriage. The relationship between the centerline, which
is being tracked by the nose wheel, and position of the main under-
carriage are shown in Fig. 6-36. At any point on the curve the distance
between the curved path followed by the nose wheel and the mid-
point of the undercarriage of main landing gear is referred to as the