What is an Object Free Area (OFA)?
An object free area (OFA) is an area around a runway, taxiway or taxilane that stays clear of objects.
Definition
The FAA defines an object free area in AC 150/5300-13B as an area centred on a runway, taxiway or taxilane centerline. It stays clear of objects to make aircraft operations safer. Two kinds of object may stand in it. Air navigation needs the first kind. Aircraft ground maneuvering needs the second.
The AC gives the word “object” a wide meaning. It includes above-ground structures, navigation aids, equipment, vehicles, natural growth, terrain, and parked or taxiing aircraft. The purpose is wingtip clearance. Pilots cannot see their wingtips from the cockpit, so the area gives room for an aircraft that wanders off the centerline.
The three kinds of OFA
The FAA uses one name for three areas that differ in size.
- Runway object free area (ROFA). It is symmetrical about the runway centerline. It gives wingtip protection if an aircraft leaves the runway. The dimensions depend on the runway design code and are in Appendix G of the AC. The obstacle free zone page lists the values for one runway group and explains how the ROFA differs from the OFZ.
- Taxiway object free area (TOFA). It is symmetrical about the taxiway centerline and sits next to the taxiway safety area.
- Taxilane object free area (TLOFA). It is the same area for a taxilane. A taxilane is a low-speed taxi path, so its area is narrower.
The FAA says that taxiways usually lie in movement areas and taxilanes are more common in non-movement areas, such as terminal aprons. The OFA is one of the four standards that differ between a taxiway and a taxilane (AC 150/5300-13B, 4.1.1). The others are centerline separation, centerline to object distance and wingtip clearance.
How wide is a taxiway or taxilane OFA?
The airplane design group (ADG) of the critical aircraft sets the width. Table 4-1 of the AC bases the values on the wingspan of the group, a lateral deviation allowance and a safety buffer. The OFA width is twice the centerline to object distance in the same table.
| ADG | Taxiway safety area (TSA) | Taxiway OFA (TOFA) | Taxilane OFA (TLOFA) |
|---|---|---|---|
| I | 14.9 m (49 ft) | 27.1 m (89 ft) | 24.1 m (79 ft) |
| II | 24.1 m (79 ft) | 37.8 m (124 ft) | 33.5 m (110 ft) |
| III | 36.0 m (118 ft) | 52.1 m (171 ft) | 48.2 m (158 ft) |
| IV | 52.1 m (171 ft) | 74.1 m (243 ft) | 68.3 m (224 ft) |
| V | 65.2 m (214 ft) | 86.9 m (285 ft) | 82.3 m (270 ft) |
| VI | 79.9 m (262 ft) | 102.1 m (335 ft) | 98.1 m (322 ft) |
Half of the TOFA is the distance from the taxiway centerline to a fixed or movable object. For ADG III it is 26.1 m (85.5 ft), which is half of 52.1 m (171 ft).
Where two parallel taxiways serve groups that differ, add half of the larger OFA to half of the wingspan of the smaller group. For ADG III beside ADG II, half of the ADG III TOFA is 26.1 m (85.5 ft). Half of the ADG II wingspan is 12.0 m (39.5 ft). The centerline separation is 38.1 m (125 ft) (4.5.2).
What may stand inside an OFA
The rules differ by area.
- Taxiway and taxilane. The area stays clear of roads for baggage carts, fuel trucks and other service vehicles. It stays clear of parked aircraft and other objects. Objects that air navigation or ground maneuvering needs are the exception. A vehicle may operate in it. The driver must keep a safe distance ahead of or behind an aircraft, or leave the area to let the aircraft pass (4.5.4).
- Runway. The area is clear of above-ground objects that stick up above the nearest point of the runway safety area. It is clear of parked aircraft and vehicles. Taxiing and holding aircraft do not violate it. PAPI power control units and supplemental wind cones may stand in it if there is no wingtip conflict. A drainage headwall may stand in it. It must be no more than 76 mm (3 in) above the nearest point of the safety area (3.12.1).
- Service roads. The FAA places a vehicle service road outside the TSA, the TOFA, the TLOFA and the ROFA. A road may cross a taxiway or taxilane where it must (6.5.2).
OFA at turns and intersections
The area widens at intersections and turns. The extra width is (TOFA width minus W) divided by 2, measured from the taxiway edge, where W is the taxiway width. The distance follows the fillet design. For example, take a TOFA of 171 ft (52.1 m) and a taxiway 50 ft (15.2 m) wide. The extra width is (171 minus 50) divided by 2, which is 60.5 ft (18.4 m).
OFA, safety area and OFZ
Three clearing standards sit next to each other, and they protect different things.
- Safety area. It is the prepared surface next to the pavement. The safety area page covers it. The TOFA starts where the TSA ends.
- Object free area. It is the wider area beside the safety area. It stays clear of objects.
- Obstacle free zone (OFZ). It is airspace and not ground. It protects an aircraft on final approach and in a missed approach.
The ICAO and EASA equivalent
ICAO and EASA do not call the area an object free area. They use the taxiway strip, which is an area that includes a taxiway. It protects an aircraft on the taxiway and reduces the risk of damage to an aircraft that runs off the taxiway. Annex 14, 3.11.1, puts every taxiway in a strip, except an aircraft stand taxilane.
ICAO Recommends that the strip provides an area clear of objects that may endanger taxiing aeroplanes (3.11.3). CS ADR-DSN.D.320 says the same. The strip extends on each side of the centre line to at least the distance in column 11 of the separation table (3.11.2, CS ADR-DSN.D.315). Column 11 is the distance from the taxiway centre line to an object:
| Code letter | Distance from centre line |
|---|---|
| A | 15.5 m |
| B | 20 m |
| C | 26 m |
| D | 37 m |
| E | 43.5 m |
| F | 51 m |
ICAO and EASA set these values by code letter. The FAA sets its values by airplane design group. The two systems group aircraft differently, so do not read a code letter as an ADG.
What an OFA means on an airfield
The OFA decides where an operator may place equipment, signs, lights and roads next to a pavement. It also decides where a vehicle may drive and where an aircraft may park. A larger critical aircraft widens the area. The operator has to move or accept everything inside it.
On a terminal apron, the FAA uses the taxilane OFA to place the non-movement area boundary marking. The FAA sets the marking back by the centerline to object criteria. The FAA usually uses taxilane criteria for it, because aircraft taxi at lower speeds there (AC 150/5340-1M, 5.4).
What to do
- Find the critical aircraft of each taxiway and taxilane, and take its ADG.
- Keep parked aircraft, parked vehicles, stored equipment and service roads outside the area.
- Let a vehicle enter only if it gives way to aircraft.
- If a fixed object must stand in the area, check that its function needs it there. Check the same for a new object.
- Re-check the area when the critical aircraft changes, because the width changes with the group.
Frequently Asked Questions
- What is the taxiway object free area?
- The taxiway object free area (TOFA) is the area on both sides of a taxiway centerline. It must stay clear of objects that are not fixed by function. It gives wingtip clearance. The FAA sets its width by airplane design group, from 27.1 m (89 ft) for group I to 102.1 m (335 ft) for group VI.
- What is an object free area?
- An object free area is an area centred on a runway, taxiway or taxilane centerline. It stays clear of objects to protect aircraft operations. Only objects that air navigation or aircraft ground maneuvering needs may stand in it. The FAA defines the term in AC 150/5300-13B.
- How wide is the taxiway object free area?
- It depends on the airplane design group (ADG) of the critical aircraft. The area is symmetrical about the centerline. The FAA gives these widths. ADG I is 27.1 m (89 ft) and II is 37.8 m (124 ft). III is 52.1 m (171 ft) and IV is 74.1 m (243 ft). V is 86.9 m (285 ft) and VI is 102.1 m (335 ft).
- How wide is the taxilane object free area?
- It is narrower than the taxiway value for the same group. The FAA gives these widths. ADG I is 24.1 m (79 ft) and II is 33.5 m (110 ft). III is 48.2 m (158 ft) and IV is 68.3 m (224 ft). V is 82.3 m (270 ft) and VI is 98.1 m (322 ft).
- What is the difference between an OFA and an OFZ?
- An OFA is an area on the ground. An OFZ is a volume of airspace above the approach and the runway. The FAA also defines the runway object free area (ROFA), which is the OFA of a runway. It protects the wingtips of an aircraft that leaves the runway.
- What is the difference between an OFA and a safety area?
- A safety area is next to the pavement. The TOFA is next to the taxiway safety area (TSA), so it is wider. The FAA sets the TSA at the maximum wingspan of the group. The TOFA adds clearance beyond it.
- Can a vehicle or aircraft stand in an object free area?
- A vehicle may operate in a taxiway or taxilane OFA if it gives way to an oncoming aircraft. Parked aircraft may not stand in it. In the runway OFA, taxiing and holding aircraft do not violate the standard. That area must stay clear of parked aircraft and vehicles.
- Do ICAO and EASA have an object free area?
- They use the taxiway strip. ICAO Annex 14 and EASA CS ADR-DSN.D.320 say that the strip should provide an area clear of objects that may endanger taxiing aeroplanes. By code letter, the strip extends at least 15.5 m to 51 m from the centre line.
References
- faa-ac-150-5300-13b
- AC 150/5300-13B, Airport Design (Change 1) FAA
- faa-ac-150-5340-1m
- AC 150/5340-1M, Standards for Airport Markings FAA
- 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
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