![](media/image1.png){width="1.0090277777777779in"
height="1.0097222222222222in"} Effective Date:

> October 6, 2005

**SUBJ:** Standard Naming Convention for Aircraft Landing Gear
Configurations

**1. Purpose of This Order.** This Order establishes a standard
convention for naming and characterizing aircraft landing gear
configurations. Although this order is primarily directed at fixed wing
airplanes, it is applicable to any aircraft using wheels for landing
purposes.

**2. Who This Order Affects.** This Order impacts divisions in the
Offices of Planning and Programming, Airport Safety and Standards, Air
Traffic, Airway Facilities, and Flight Standards Services; the regional
Airports, Air Traffic, Airway Facilities, and Flight Standards
Divisions; and Airport District and Field Offices. It will also affect
organizations and individuals external to the Federal Aviation
Administration (FAA). A standardized naming convention will allow
uniformity and consistency among Federal agencies and external entities
when naming aircraft gear configurations. Pilots and airport operators
will no longer need to learn multiple naming systems and will be able to
use common aircraft landing gear names at all military and commercial
facilities.

**3. Background of This Order.** Landing gear configuration and aircraft
gross weight are an integral part of airfield pavement design and are
often used to characterize pavement strength. Historically, most
aircraft used relatively simple gear geometries such as a single wheel
per strut or two wheels side by side on a landing strut. As aircraft
became larger and heavier, they required additional wheels to prevent
individual wheel loads from introducing excessively high stresses into
the pavement structure. For economy and efficiency reasons, aircraft
manufacturers added more wheels per landing strut whenever possible.
This often led to groups of wheels placed side-by-side and in tandem
configurations.

**a. Typical Gear Configurations.** Up until the late 1980s, the
majority of civilian and military aircraft used three basic gear
configurations: the "single wheel" (one wheel per strut), the "dual
wheel" (two wheels side by side on a strut), and the "dual tandem" (two
wheels side by side followed by two additional side-by-side wheels). As
aircraft continued to increase in gross weight, manufacturers attempted
to limit the damage imparted to pavements by increasing the total number
of wheels. This was typically done by adding additional landing struts
to the aircraft. For example, McDonnell Douglas originally manufactured
the DC-10 with two landing struts using the dual tandem gear
configuration. When the company produced the heavier DC-10-30 variation
of the aircraft, it added an additional landing strut, using a dual
wheel configuration, to the center of the aircraft. Another example is
the Boeing 747 aircraft. To reduce the impact to airfield pavements,
Boeing used four landing struts with dual tandem configurations on the
B-747.

**b. Complex Gear Configurations.** The increasingly complex gear
arrangements quickly outgrew the simple single, dual, and dual tandem
descriptions. Additionally, other aircraft were developed with gear
configurations that used numerous wheels in arrangements that could not
be described by the three simple gear configurations. As the number and
complexity of gear arrangements increased and with no coordinated effort
to provide a uniform naming convention, the FAA, U.S. Air Force, and
U.S. Navy developed different naming systems that were not easily
cross-referenced.

**4. Definitions Used in This Order.**

**a. Main Gear.** "Main gear" means the primary landing gear that is
symmetrical on either side of an aircraft. When multiple landing gears
are present and are not in line with each other, the outer most gear
pair is considered the main gear. Multiples of the main gear exist when
a gear is in line with other gears along the longitudinal axis of the
aircraft.

**b. Body/Belly Gear.** "Body/belly gear" refers to an additional
landing gear or gears in the center portion of the aircraft between the
main gears. Body/belly gears may be of a different type than the main
gear and may be nonsymmetrical.

**5. Intended areas of use.** The naming convention shown in Figure 1 is
intended for use in all civilian and military applications. All FAA
pavement design guidance and FAA databases and database publications,
e.g. 5010 Master Record, Airport/Facilities Directory, etc., will
hereafter use the described aircraft gear naming convention. The Air
Force and Navy will also adopt this system in their pavement guidance
and facilities databases.

**6. Aircraft Gear Geometry Naming Convention.**

**a. Basic Name for Aircraft Gear Geometry.** Under the naming
convention, abbreviated aircraft gear designations may include up to
three variables: the main gear configuration, the body/belly gear
configuration if body/belly gears are present, and an optional tire
pressure code described below. Figure 1 illustrates the two primary
variables.

**b. Basic Gear Type.** Gear type for an individual landing strut is
determined by the number of wheels across a given axle (or axle line)
and whether wheels are repeated in tandem. There may exist, however,
instances in which multiple struts are in close proximity and are best
treated as a single gear, e.g. Antonov AN-124 (see Figure 14). If
body/belly gears are not present, the second portion of the name is
omitted. For aircraft with multiple gears, such as the B-747 and the
A380, the outer gear pair is treated as the main gear.

**c. Basic Gear Codes.** This naming convention uses the following codes
for gear designation purposes (see Figure 2):

  ------------------------ ----------------------------------------------
  S                        Single

  D                        Dual

  T                        Triple

  Q                        Quadruple
  ------------------------ ----------------------------------------------

**d. Use of Historical Tandem Designation.** Although the verbal
description continues to use the term "tandem" to describe tandem gear
configurations, the tandem designation "T" no longer appears in the gear
name. "T" now indicates triple wheels.

\# X \# **/** \# X \#

Figure 1. Aircraft Gear Naming Convention

**e. Main Gear Portion of Gear Designation.** The first portion of the
aircraft gear name comprises the main gear designation. This portion may
consist of up to three characters. The first character indicates the
number of tandem sets or wheels in tandem, e.g. 3D = three dual gears in
tandem. (If a tandem configuration is not present, the leading value of
"1" is omitted.) Typical names are S = Single, 2D = two dual wheels in
Tandem, 5D = five dual wheels in tandem, and 2T = two triple wheels in
tandem.

**(1)** The second character of the gear designation indicates the gear
code, e.g. S, D, T, or Q.

**(2)** The third character of the gear designation is a numeric value
that indicates multiples of gears. For the main gear, the gear
designation assumes that the gear is present on both sides (symmetrical)
of the aircraft and that the reported value indicates the number of
gears on one side of the aircraft. A value of 1 is used for aircraft
with one gear on each side of the airplane. For simplicity, a value of 1
is assumed and is omitted from the main gear designation. Aircraft with
more than one main gear on each side of the aircraft and where the gears
are in line will use a value indicating the number of gears in line. For
example, the Ilyushin IL-76 has two gears containing quadruple wheels on
each side of the aircraft and is designated as a Q2 (see Figure 20).

**f. Body/Belly Gear Portion of Gear Designation.** The second portion
of the aircraft gear name is used when body/belly gears are present. If
body/belly gears are present, the main gear designation is followed by a
forward slash (/), then the body/belly gear designation. For example,
the B-747 aircraft has a two dual wheels in tandem main gear and two
dual wheels in tandem body/belly gears. The full gear designation for
this aircraft is 2D/2D2. The body/belly gear designation is similar to
the main gear designation except that the trailing numeric value denotes
the total number of body/belly gears present, e.g. 2D1 = one dual tandem
body/belly gear; 2D2 = two dual tandem body/belly gears. Because
body/belly gear arrangement may not be symmetrical, the gear code must
identify the total number of gears present, and a value of 1 is not
omitted if only one gear exists.

**g. Extension of Naming Convention.** Future aircraft might require
additional body/belly gears that are nonsymmetrical and/or nonuniform.
In these instances, the body/belly gear designation will contain a
hyphen to indicate the nonuniform gear geometry. For demonstration
purposes, consider adding one dual wheel body/belly gear to the existing
2D/2D2 gear configuration. The resulting gear name would be 2D/2D2-D.

**h. Unique Gear Configurations.** The Lockheed C-5 Galaxy has a unique
gear type and is difficult to name using the proposed method. This
aircraft will not be classified using the new naming convention and will
continue to be referred to directly as the C5. Gear configurations such
as those on the Boeing C-17, Antonov AN-124, and Ilusyin IL-76 might
also cause some confusion; see Figures 8, 14, and 20, respectively. In
these cases, it is important to observe the number of landing struts and
the proximity of the struts. In the case of the AN-124, it is more
advantageous to address the multiple landing struts as one gear, i.e. 5D
or five duals in tandem, rather than use D5 or dual wheel gears with
five sets per side of the aircraft. Due to wheel proximity, the C-17
gear is more appropriately called a 2T as it appears to have triple
wheels in tandem. In contrast, the IL-76 has considerable spacing
between the struts and should be designated as a Q2.

**i. Examples of Gear Geometry Naming Convention.** Figure 2 provides
examples of generic gear types in individual and multiple tandem
configurations. Figures 3 through 20 provide examples of known gear
configurations.

**j. Comparison of Naming Convention to Historical Procedures.** Table 3
demonstrates the proposed naming convention and references the historic
FAA, U.S. Air Force, and U.S. Navy methods. The historic Air Force
methodology also addresses the configuration of the aircraft nose gear.
Due to the insignificance of the pavement load imposed by the nose gear,
the proposed method does not address nose gear configuration.

**k. Inclusion of Tire Pressure Information.** In addition to specifying
gear geometry, the aircraft gear designation can also indicate the tire
pressures at which the aircraft operates. Although tire pressure effects
on airfield pavements are secondary to aircraft load and wheel spacing,
they can have a significant impact on the ability of the pavement to
accommodate a specific aircraft.

**(1)** The Aircraft Classification Number (ACN) and the Pavement
Classification Number (PCN) system created by the International Civil
Aviation Organization (ICAO) has defined and categorized aircraft tire
pressures into four groups for reporting purposes. Table 1 lists these
groups and their assigned codes.

Table 1. Standard Tire Pressure Categories

  ------------------- ---------------- ---------------- -------------------
  Category            Range                             Code Designation

                      psi              MPa              

  High                No limit         No Limit         W

  Medium              146 - 217        1.01 - 1.5       X

  Low                 74 - 145         0.51 - 1.0       Y

  Very Low            0 - 73           0.0 - 0.5        Z
  ------------------- ---------------- ---------------- -------------------

**(2)** To allow for the reporting of tire pressure, the gear naming
convention includes a third variable. Using the codes identified by the
International Civil Aviation Organization (ICAO), the tire pressure can
be included in parentheses after the standard gear nomenclature. Table 2
provides sample gear names with and without the additional tire pressure
code.

Table 2. Sample Gear Names With and Without Tire Pressure Codes

  ----------------------------------- -----------------------------------
  Gear Name Without Tire Pressure     Gear Name With Tire Pressure

  S                                   S(W)

  2S                                  2S(X)

  2D/2D1                              2D/2D1(Z)

  Q2                                  Q2(Y)

  2D/3D2                              2D/3D2(Z)
  ----------------------------------- -----------------------------------

## Table 3. Proposed Naming Convention with Historical FAA, U.S. Air Force, and U.S. Navy Nomenclatures

![](media/image2.wmf)

![](media/image3.wmf){width="5.840972222222222in"
height="6.128472222222222in"}

Figure 2. Generic Gear Configurations. Increase numeric value for
additional tandem axles.

![](media/image4.wmf){width="1.7583333333333333in"
height="1.9993055555555554in"}

Figure 3. S - Single Wheel Main Gear with Single Wheel Nose Gear

![](media/image5.wmf){width="2.2736111111111112in"
height="1.9993055555555554in"}

Figure 5. D - Dual Wheel Main Gear with Single Wheel Nose Gear

![](media/image6.wmf){width="1.4569444444444444in"
height="2.0076388888888888in"}

Figure 7. 2S - Two Single Wheels in Tandem Main Gear with Dual Wheel
Nose Gear, Lockheed C-130

![](media/image7.wmf){width="1.3256944444444445in" height="2.0125in"}

Figure 4. S - Single Wheel Main Gear with Dual Wheel Nose Gear

![](media/image8.wmf){width="2.1979166666666665in"
height="2.0076388888888888in"}

Figure 6. D - Dual Wheel Main Gear with Dual Wheel Nose Gear

![](media/image9.wmf){width="1.7833333333333334in"
height="1.9993055555555554in"}

Figure 8. 2T - Two Triple wheels in Tandem Main Gear with Dual Wheel
Nose Gear, Boeing C-17

![](media/image10.wmf){width="1.8340277777777778in"
height="1.9993055555555554in"}

Figure 9. 2D - Two Dual Wheels in Tandem Main Gear with Dual Wheel Nose
Gear

![](media/image11.wmf){width="1.8340277777777778in"
height="1.9993055555555554in"}

Figure 11. 2D/2D1 Two Dual Wheels in Tandem Main Gear/Two Dual Wheels in
Tandem Body Gear with Dual Wheel Nose Gear, Airbus A340-600

![](media/image12.wmf){width="1.6958333333333333in"
height="1.9993055555555554in"}

Figure 13. 3D - Three Dual Wheels in Tandem Main Gear with Dual Wheel
Nose Gear, Boeing B-777

![](media/image13.wmf){width="1.8340277777777778in"
height="1.9993055555555554in"}

Figure 10. 2D/D1 - Two Dual Wheels in Tandem Main Gear/Dual Wheel Body
Gear with Dual Wheel Nose Gear, McDonnell Douglas DC-10, Lockheed L-1011

![](media/image14.wmf){width="1.8840277777777779in"
height="1.9993055555555554in"}

Figure 12. 2D/2D2 - Two Dual Wheels in Tandem Main Gear/Two Dual Wheels
in Tandem Body Gear with Dual Wheel Nose Gear, Boeing B-747

![](media/image15.wmf){width="1.7958333333333334in"
height="3.0118055555555556in"}

Figure 14. 5D - Five Dual Wheels in Tandem Main Gear with Quadruple Nose
Gear, Antonov AN-124

![](media/image16.wmf){width="1.6958333333333333in"
height="1.9993055555555554in"}

Figure 16. 2D/3D2 - Two Dual Wheels in Tandem Main Gear/Three Dual
Wheels in Tandem Body Gear with Dual wheel Nose Gear, Airbus A380

![](media/image17.wmf){width="1.570138888888889in"
height="2.9340277777777777in"}

Figure 15. 7D - Seven Dual Wheels in Tandem Main Gear with Quadruple
Nose Gear, Antonov AN-225

![](media/image18.wmf){width="1.5451388888888888in"
height="2.0076388888888888in"}

Figure 17. C5 - Complex Gear Comprised of Dual Wheel and Quadruple Wheel
Combination with Quadruple Wheel Nose Gear, Lockheed C5 Galaxy

![](media/image19.wmf){width="2.9138888888888888in"
height="1.895138888888889in"}

Figure 18. D2 - Dual Wheel Gear Two Struts per Side Main Gear with No
Separate Nose Gear (note that single wheel outriggers are ignored),
Boeing B-52 Bomber

![](media/image20.wmf){width="2.7256944444444446in" height="2.40625in"}

Figure 20. Q2 - Quadruple Wheels Two Struts per Side with Quadruple Nose
Gear, Ilyushin IL-76

![](media/image21.wmf){width="2.948611111111111in"
height="1.9701388888888889in"}

Figure 19. Q - Quadruple Wheel Main Gear with Dual Wheel Nose Gear,
Hawker Siddeley HS-121 Trident

# ![](media/image22.png){width="2.748611111111111in" height="0.5506944444444445in"}

# 

# David L. Bennett

Director of Airport Safety and Standards