This video provides an overview of
Basic Taxiway Design by the Office of Airports
at the Federal Aviation Administration.
For information on Basic Taxiway Design,
refer to Advisory Circular 150/5300-13,
Airport Design, for specific design standards.
See www.faa.gov.
Images in this video are graphical representations
only and are not to scale.
Discussion topics include:
Design Groups,
Taxiway Standards on Straight Sections,
Taxiway Separation Standards,
and Taxiway Intersection Geometry.
The FAA uses two distinct design groups
for determining taxiway design standards:
Taxiway Design Group, or TDG,
and Airplane Design Group, or ADG.
TDGs are groupings of aircraft based on undercarriage
gear dimensions comprised of the main gear width,
or MGW, and cockpit to main gear, or CMG, distance.
There are six TDGs based on groupings of similar MGW.
The X axis of the graph and CMG length, the Y axis of the graph.
As examples, the 737-900 aircraft falls into TDG 3,
while the 777-300 falls into the larger TDG 6
due to its wider MGW and longer CMG dimension.
The TDG defines specific design parameters for taxiway design.
For example,
the TDG 3 and TDG 6 design parameters
shown here are used for specific taxiway design
elements for each TDG group, as described in this video.
ADGs are groupings of similar-sized aircraft
based on tail height and aircraft wingspan
with each ADG defined by ranges for these
two dimensions as shown.
As an example, ADG 5 includes aircraft
with a tail height between 60 and 66 feet,
and wingspans between 171 and 214 feet
while ADG 3 includes aircraft with a tail height
between 30 and 45 feet,
and wingspans between 79 and 118 feet.
Taxiway standards based on TDG include taxiway width,
taxiway edge safety margin, or TESM,
shoulder width,
and fillet design for taxiway curves.
Taxiway standards based on ADG include taxiway safety area,
object free area, or OFA, and separation distance.
In general,
taxiway standards increase in size
as TDG and ADG categories increase.
Taxiways provide a route for an aircraft taxiing
from one part of an airport to another
with typical taxiing speeds of 15 to 35 miles per hour.
Taxilanes provide a route for taxiing
and maneuvering of aircraft near passenger
terminals and aircraft parking stands,
with typical taxiing speeds not exceeding 15 mph.
Because of these lower taxiing speeds,
certain taxilane design standards are
less stringent than taxiway standards.
For taxiway dimensions on straight taxiway sections
standards based on TDG include
the taxiway width and the taxiway shoulder width
while standards based on ADG include
the taxiway safety area and the taxiway OFA.
The taxiway safety area is a defined surface extending beyond
the standard taxiway pavement on both sides of the taxiway.
The taxiway safety area width
is equal to the ADG maximum wingspan dimension.
The taxiway safety area surface beyond the pavement supports
the occasional passage of aircraft,
snow removal equipment,
and aircraft rescue and fire fighting equipment.
The taxiway safety area is kept clear of objects
except for those located in the taxiway safety area
because of their function.
Taxiway safety areas are also graded to
prevent accumulation of standing water.
The FAA bases the taxiway OFA for each ADG group
on an established wingtip clearance
to moveable objects such as taxiing aircraft
or service vehicles, and to fixed objects such as buildings
or non-fixed by function NAVAID facilities.
In the passenger terminal area,
the taxilane OFA provides clearance to parked aircraft,
vehicle service roads,
and other objects on both sides of the taxilane.
Taxiway OFA dimensions are based on
a lateral deviation distance from the taxiway centerline,
plus half the ADG wingspan,
plus a safety buffer to provide wingtip
clearance to fixed or moveable objects.
For example,
ADG 5 design parameters include a lateral
deviation distance of 14.5 feet,
half the ADG wingspan of 107 feet,
and a safety buffer of 21 feet.
The sum of these three values equals half the OFA width,
or 142.5 feet,
with the resulting full taxiway OFA width of 285 feet.
For taxiway curves,
additional fillet pavement is necessary on the
inside of the curve since aircraft gear tracks to
the inside of the taxiway centerline when turning.
Because of this additional fillet pavement,
the taxiway safety area and taxiway OFA
extend further from the taxiway centerline on
the inside of the curve to maintain the standard
taxiway safety area and taxiway OFA widths.
For separation standards between parallel taxiways
the FAA establishes taxiway separation as follows:
one of the two aircraft deviates from the taxiway centerline,
while the other aircraft remains on the centerline.
The taxiway separation distance incorporates
the ADG wingspans, a lateral deviation distance,
and a safety buffer distance,
resulting in adequate wingtip
clearance between the two aircraft.
This example shows two ADG 5 taxiways
with a lateral deviation of 14.5 feet,
half the ADG wingspan of 107 feet for both aircraft,
and a safety buffer of 21 feet,
resulting in a taxiway separation distance of 249 feet.
In this example,
parallel taxiways designed for the same ADG 5
have a separation distance of 249 feet
which ensures adequate wingtip clearance
between the two taxiing aircraft.
For parallel taxiways designed for different ADGs,
calculate the separation distance by
adding half the taxiway OFA of the larger ADG taxiway
to the aircraft wingspan for the smaller ADG taxiway.
This taxiway separation maintains wingtip clearance
between the two aircraft.
In the example,
half the ADG 5 taxiway OFA,
which is 142.5 feet,
added to half the ADG 3 wingspan,
which is 59 feet,
obtains the separation distance of 201.5 feet
between an ADG 5 and ADG 3 taxiway.
When designing basic taxiway intersection geometry,
standard practices for taxiway design
limit the number of taxiways intersecting at a single location.
This allows for proper placement of airfield markings,
signage,
and lighting.
The “three-path concept”,
previously referred to as the “three-node concept”,
means that a pilot does not have more than three
choices at an intersection:
left, right, and forward.
Taxiway intersection designs include a range of angles.
Optimal intersections are ninety-degree intersections
that provide pilots with clear markings,
signage,
and sightlines to safely cross taxiways.
Designing for other taxiway intersection angles
is acceptable to address
an airport’s geometric constraints and needs.
Design of acute angle intersections
should consider fillet requirements,
the turn capabilities of the design aircraft,
standard markings,
lighting,
signage,
and the pilot’s field of view.
Base taxiway intersection design on
cockpit-over-centerline steering where the
pilot maintains the cockpit over the
taxiway centerline while turning.
As shown,
the aircraft’s main gear tracks to the inside
of the taxiway turn, therefore requiring
additional taxiway fillet pavement on
the inside of the curve.
These reference materials provide
guidance on taxiway design.
Visit www.faa.gov
to find these documents,
videos, and related design tools.
For additional information,
contact the FAA’s Office of Airports.
The FAA appreciates your interest.
Safe flying.