Taxiways and Taxilanes

Taxiways and Taxilanes

Taxiways are defined paths on the airfield surface which are established for the taxiing of aircraft and are intended to provide a linkage between one part of the airfield and another taxiways refers to two taxiways parallel to can taxi in opposite directions. An apron taxiway is a taxiway located usually on the periphery of an apron intended to provide a through taxi route across the apron. A taxilane is a portion of the aircraft parking area used for access between the taxiways and the aircraft parking positions. ICAO defines an aircraft stand taxilane as a portion of the apron intended to provide access to the aircraft stands only.

In order to provide a margin of safety in the airport operating areas, the trafficways must be separated sufficiently from each other and from adjacent obstructions. Minimum separations between the centerlines of taxiways, between the centerlines of taxiways and taxilanes, and between taxiways and taxilanes and objects are specified in order that aircraft may safely maneuver on the airfield.

Widths and Slopes

Since the speeds of aircraft on taxiways are considerably less than on runways, criteria governing longitudinal slopes, vertical curves, and sight distance are not as stringent as for runways. Also the lower speeds permit the width of the taxiway to be less than that of the runway.

aFor airplanes in airplane design group III with a wheelbase equal to or greater than 60 ft, the standard taxiway width is 60 ft.

bThe taxiway edge safety margin is the minimum acceptable between the outside of the airplane wheels and the pavement edge.

cFor airplanes in airplane design group III with a wheelbase equal or greater than 60 ft, the taxiway edge safety margin is 15 ft.

dAirplanes in airplane design groups V and VI normally stabilized or paved taxiway shoulder surfaces.

eMay use aircraft wingspan in lieu of these values. fMay use 1.4 wingspan plus 20 ft in lieu of these values. gMay use 1.2 wingspan plus 20 ft in lieu of these values.

 hMay use 1.2 wingspan plus 10 ft in lieu of these values. iMay use 0.7 wingspan plus 10 ft in lieu of these values. jMay use 1.1 wingspan plus 10 ft in lieu of these values. kMay use 0.6 wingspan plus 10 ft in lieu of these values.

Taxiway and Taxilane Separation Requirements FAA Separation Criteria

The separation criteria adopted by the FAA are predicated upon the wingtips of the aircraft for which the taxiway and taxilane system have been designed and provide a minimum wingtip clearance on these facilities. The required separation between taxiways, between a taxiway and a taxilane, or between a taxiway and a fixed or movable object requires a minimum wingtip clearance of 0.2 times the wingspan of the most demanding aircraft in the airplane design group plus 10 ft. This clearance provides a minimum taxiway centerline to a parallel taxiway centerline or taxilane centerline separation of 1.2 times the wingspan of the most demanding aircraft plus 10 ft, and between a taxiway centerline and a fixed or movable object of 0.7 times the wingspan of the most demanding aircraft plus 10 ft.

*A minimum of 3 percent for turf.

†A slope of 5 percent-ftwidthisadjacentrecommendedtothepavementareasto for a 1 promote drainage.

‡Foreach   1   percent   of   grade   change.

§Distance is multiplied by the sum of the absolute grade changes in percent.

*18 m if used by aircraft with a wheelbase equal to or greater than 18 m.

†23 m is used by aircraft with an outer main ‡4.5 m. if intended to be used by airplane w separation is also applicable to aircraft traversing through a taxiway on an apron or ramp. This separation may have to be increased to accommodate pavement widening on taxiway curves. It is recommended that a separation of at least 2.6 times the wheelbase of the most demanding aircraft be provided to accommodate a 180turn  when the pavement width is designed for tracking the nose wheel on the centerline.

The taxilane centerline to a parallel taxilane centerline or fixed or movable object separation in the terminal area is predicated on a wingtip clearance of approximately half of that required for an apron taxiway. This reduction in clearance is based on the consideration that taxiing speed is low in this area, taxiing is precise, and special guidance techniques and devices are provided. This requires a wingtip clearance or wingtip-to-object clearance of 0.1 times the wingspan of the most demanding aircraft plus 10 ft. Therefore, this establishes a minimum separation between the taxilane centerlines of 1.1 times the wingspan of the most demanding aircraft plus 10 ft, and between a taxilane centerline and a fixed or movable object of 0.6 times the wingspan of the most demanding aircraft plus 10 ft [6]. Therefore, when dual parallel taxilanes are provided in the terminal apron area, the taxilane object-free area becomes 2.3 the wingspan of the most demanding aircraft plus 30 ft.

The separation criteria adopted by ICAO are also predicated upon the wingtips of the aircraft for which the taxiway and taxilane system have been designed and providing a minimum wingtip clearance on these facilities, but also consider a minimum clearance between the outer main gear wheel and the taxiway edge. The required separation between taxiways or between a taxiway and a taxilane requires a minimum wingtip clearance, C1, of 3 m for aerodrome code letter

A and B runways, 4.5 m for aerodrome code letter C runways, and 7.5 m for aerodrome code letter D and E runways. The minimum clearance between the edge of each taxiway and the outer main gear wheels, the taxiway edge safety margin U1, is given in Table 6-20. This clearance provides a minimum taxiway centerline to a parallel taxiway centerline or taxilane centerline separation given by.

STT   WS    2U1   C1 (6-1)

where STT  minimum taxiway-to-taxiway or taxiway-to-taxilane

separation           

WS    wingspan of the most demanding aircraft

U1     taxiway edge safety margin

C1     minimum wingtip clearance

Therefore, for example, an ICAO aerodrome code letter E runway, which accommodates aircraft with wingspans up to 65 m,

requires a taxiway centerline to a taxiway centerline or a taxilane centerline

separation from Eq. (6-1) of 65

2(4.5)          7.5     81.5 m.

The required separation between a taxiway centerline or an apron taxiway centerline and a fixed or movable object is found from Eq. (6-2).

STO0.5 WSU1C2 (6-2)

where STO is the minimum taxiway or apron taxiway to a fixed or movable object separation and C2 is the required clearance between a wingtip and an object.

The required clearance between a wingtip and an object C2 is 4.5 m for aerodrome code letter A runways, 5.25 m for aerodrome code letter B runways, 7.5 m for aerodrome code letter C runways, and 12 m

for aerodrome code letter D and E runways.

The required separation between an aircraft stand taxilane centerline and a fixed or movable object is found from Eq. (6-3).

SATO0.5 WSU2C1 (6-3)

where SATO is the minimum aircraft stand taxilane to fixed or movable object separation and U2 is the aircraft stand safety margin.

Since aircraft moving on the aircraft stand taxilane are moving at low speed and are often under positive ground guidance, the aircraft stand safety margin is less than on the taxiway system.

The value for this safety margin U2 is 1.5 m for aerodrome code letter A and B airports, 2 m for aerodrome code letter C airports, and 2.5 m for aerodrome code letter D or E airports. The taxiway and taxilane separation criteria adopted by ICAO are given in Table 6-20.

Sight Distance and Longitudinal Profile

As in the case of runways, the number of changes in longitudinal profile for taxiways is limited by sight distance and minimum distance between vertical curves.

The FAA does not specify line of sight requirements for taxiways other than those discussed earlier related to runway and taxiway intersections. However, the sight distance along a runway from an intersecting taxiway needs to be sufficient to allow a taxiing aircraft to

enter or cross the runway safely. The FAA specifies that from any point on the taxiway centerline the difference in elevation between that

point and the corresponding point on a parallel runway, taxiway, or apron edge is 1.5 percent of the shortest distance between the points. ICAO requires that the surface of the taxiway should be seen for a distance of 150 m from a point 1.5 m above the taxiway for aerodrome code letter A runways, for a distance of 200 m from a point 2 m above the taxiway for aerodrome code letter B runways, and for a distance of 300 m from a point 3 m above the taxiway for aerodrome code letter C, D, or E runways.

In regard to longitudinal profile of taxiways, the ICAO does not specify the minimum distance between the points of intersection of vertical curves. The FAA specifies that the minimum distance for both utility and transport category airports should be not less than the product of 100 ft multiplied by the sum of the absolute percentage values of change in slope.