What is Outer Main Gear Wheel Span (OMGWS)?
The outer main gear wheel span (OMGWS) is the distance between the outside edges of the main gear wheels of an aeroplane.
Definition
ICAO Annex 14 and EASA Regulation (EU) No 139/2014 use the same words. The OMGWS is the distance between the outside edges of the main gear wheels. It is a measure of the aeroplane, and not of the aerodrome.
The OMGWS is a width across the aeroplane at the wheels. It is not the wingspan, and it is not the wheel base. ICAO and EASA define the wheel base as the distance from the nose gear to the geometric centre of the main gear.
OMGWS and the aerodrome reference code
The aerodrome reference code has two elements. The code number comes from the aeroplane reference field length. The code letter comes from the greatest wingspan of the aeroplanes that the facility serves (Annex 14, 1.6.3 and 1.6.4).
The OMGWS is not part of the code. It is a separate input. ICAO and EASA use it with the code number for runway width, and alone for taxiway width. See aerodrome reference code .
What the OMGWS sets
- Runway width. The minimum width depends on the code number and the OMGWS (Annex 14, 3.1.10, and CS ADR-DSN.B.045). ICAO writes it as a Recommendation. The lane width page has the table and the measuring point.
- Runway shoulders. For an OMGWS from 9 m up to but not including 15 m, shoulders apply to code letter D, E or F. The runway and its shoulders together are at least 60 m wide for code D or E. They are at least 60 m for code F with two or three engines, and 75 m for four or more engines (3.2.2).
- Taxiway width. A straight taxiway has a minimum width for each OMGWS band (3.9.4, CS ADR-DSN.D.245).
- Wheel clearance. The cockpit stays over the taxiway centre line marking. The outer main wheel then needs a minimum clearance to the taxiway edge (3.9.3, CS ADR-DSN.D.240).
- Runway turn pads. The same clearance applies between any wheel and the edge of the turn pad (3.3.6).
- Taxiway strip. The graded centre portion of the strip depends on the OMGWS (3.11.4, CS ADR-DSN.D.325).
Values by OMGWS band
ICAO and EASA use four bands. The bands are the same in the taxiway and turn pad rules.
| OMGWS band | Straight taxiway width | Wheel clearance to taxiway edge |
|---|---|---|
| Below 4.5 m | 7.5 m | 1.50 m |
| 4.5 m up to 6 m | 10.5 m | 2.25 m |
| 6 m up to 9 m | 15 m | 3 m on straight portions, 3 m or 4 m on curves |
| 9 m up to 15 m | 23 m | 4 m |
On a curve, the OMGWS band of 6 m up to 9 m has two values. The clearance is 3 m if the wheel base is below 18 m. It is 4 m if the wheel base is 18 m or more.
The graded part of the taxiway strip reaches a minimum distance from the centre line. For an OMGWS of 9 m up to 15 m, the distance also depends on the code letter. ICAO gives 17 m for code D, 19 m for E and 22 m for F. EASA gives 18.5 m for D, 19 m for E and 22 m for F.
| OMGWS band | Graded strip half width (ICAO and EASA) |
|---|---|
| Below 4.5 m | 10.25 m |
| 4.5 m up to 6 m | 11 m |
| 6 m up to 9 m | 12.5 m |
ICAO says that the combinations of code number and OMGWS in the runway width table suit typical aeroplane characteristics (3.1.10, Note 1).
The FAA equivalent
The FAA uses the main gear width (MGW). It is the distance from the outer edge to the outer edge of the widest set of main gear tires (AC 150/5300-13B, definition 58). The measure is the same, and the FAA gives it in feet.
The FAA does not take the MGW alone. It combines the MGW with the cockpit to main gear distance (CMG). The result is the taxiway design group (TDG). The TDG then sets the taxiway width, the taxiway edge safety margin and the shoulder width (4.2).
| TDG | MGW limit | Taxiway width |
|---|---|---|
| 1A and 1B | up to 4.6 m (15 ft) | 7.6 m (25 ft) |
| 2A | over 4.6 m up to 6.1 m (15 to 20 ft) | 10.7 m (35 ft) |
| 2B | up to 6.1 m (20 ft) | 10.7 m (35 ft) |
| 3 | over 6.1 m up to 9.1 m (20 to 30 ft) | 15.2 m (50 ft) |
| 4 | up to 9.1 m (30 ft) | 15.2 m (50 ft) |
| 5 | over 9.1 m up to 14.3 m (30 to 47 ft) | 22.9 m (75 ft) |
| 6 | up to 14.3 m (47 ft) | 22.9 m (75 ft) |
The FAA rounds the table values to the nearest foot. The MGW limit for a group is the largest MGW in that group, and the group also has a CMG limit.
OMGWS and wingspan
Do not confuse the two. The wingspan sets the code letter. EASA also links it to taxiway separation distances and to the dimensions of the obstacle free zone. The OMGWS sets how wide the paved surface must be (AMC1 ADR.OPS.B.090(b)).
What the OMGWS means on an airfield
An aerodrome in the EU certifies its design for a code letter and an OMGWS. An aircraft that exceeds the certified code letter or the certified OMGWS needs prior approval from the competent authority (ADR.OPS.B.090(a)). An emergency is the exception. The operator should assess the OMGWS effects on several items. They are runway width, turn pad dimensions, taxiway width and taxiway fillets. They also include the dimensions of aprons and holding bays (AMC1 ADR.OPS.B.090(b)).
What to do
- Use the OMGWS band, and not the wingspan, to check runway, taxiway and turn pad widths.
- Check the widest aeroplane that uses each pavement.
- For an aeroplane that exceeds the certified OMGWS, ask for approval before operations, and include the OMGWS in the assessment.
Frequently Asked Questions
- What is OMGWS?
- OMGWS stands for outer main gear wheel span. It is the distance between the outside edges of the main gear wheels of an aeroplane. ICAO and EASA use it to size runways, taxiways, turn pads and shoulders.
- What is OMGWS used for?
- It sets how wide the pavement must be for the wheels. ICAO and EASA use it with the code number for the minimum runway width. They use it alone for taxiway width, wheel clearance, runway turn pads and the graded part of a taxiway strip. It also decides whether runway shoulders apply.
- How is the outer main gear wheel span measured?
- It is the distance between the outside edges of the main gear wheels. The FAA uses the same measure under the name main gear width (MGW). It runs from the outer edge to the outer edge of the widest set of main gear tires.
- What is the difference between OMGWS and wingspan?
- The wingspan is the distance between the wing tips. The OMGWS is the distance across the main wheels. The wingspan sets the code letter of the aerodrome reference code. The OMGWS sets pavement widths.
- How does OMGWS set the taxiway width?
- ICAO and EASA give four OMGWS bands. A straight taxiway is at least 7.5 m wide for an OMGWS below 4.5 m. It is at least 10.5 m for 4.5 m up to 6 m. It is at least 15 m for 6 m up to 9 m, and 23 m for 9 m up to 15 m.
- What does the FAA use instead of OMGWS?
- The FAA uses the main gear width (MGW). The MGW and the cockpit to main gear distance together set the taxiway design group (TDG). The TDG sets the taxiway width. It runs from 7.6 m (25 ft) for groups 1A and 1B to 22.9 m (75 ft) for groups 5 and 6.
- What happens if an aeroplane has a larger OMGWS than the aerodrome certificate allows?
- In the EU, the aerodrome operator must ask the competent authority for prior approval. ADR.OPS.B.090 requires this when an aircraft exceeds the code letter or the OMGWS of the certified design. An emergency is the exception. The request must assess the impact of the OMGWS.
References
- icao-annex-14-vol1
- Annex 14 to the Convention on International Civil Aviation, Aerodromes, Volume I, Aerodrome Design and Operations, Ninth Edition (July 2022, consolidated with later amendments) ICAO
- easa-ear-aerodromes
- Easy Access Rules for Aerodromes (Regulation (EU) No 139/2014), including CS-ADR-DSN Issue 7 EASA
- faa-ac-150-5300-13b
- AC 150/5300-13B, Airport Design (Change 1) FAA
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