obstacle-free zone

obstacle-free zone (OFZ)

The obstacle-free zone is a three-dimensional volume of airspace set up to protect aircraft transitioning to and from the runway. The OFZ clearing standard precludes taxiing and parked airplanes and object penetrations, except for frangible NAVAID (navigational aid) locations that are fixed by function. Additionally, vehicles, equipment, and personnel may be authorized by ATC (air traffic control) to enter the area in accordance with the rules in force. The runway OFZ—and when applicable, the inner-approach OFZ—and the inner-transitional OFZ, compose the OFZ. The runway OFZ is a defined volume of airspace centered above the runway. It is the airspace above a surface whose elevation at any point is the same as the elevation of the nearest point on the runway centerline. It extends 200 ft (60 m) beyond each end of the runway. The width is as follows:
i. For runways serving large airplanes, it is the greater of (a) 400 ft (120 m) or (b) 180 ft (54 m) plus the wingspan of the most demanding airplane plus 20 ft per 1000 ft of airport elevation.
ii. For runways serving only small airplanes, it is:
(a) 300 ft (90 m) for precision instrument runways.
(b) 250 ft (75 m) for other runways serving small airplanes with approach speeds of 50 knots, or more.
(c) 120 ft (36 m) for other runways serving small airplanes with approach speeds of less than 50 knots.
The inner-approach OFZ is a defined volume of airspace centered on the approach area. It applies only to runways with an approach lighting system. It begins 200 ft (60 m) from the runway threshold at the same elevation as the runway threshold and extends 200 ft (60 m) beyond the last light unit in the approach lighting system. The width of the inner-approach OFZ is the same as that of the runway OFZ, and it rises at a slope of 50 (horizontal) to 1 (vertical) from the beginning.
The inner-transitional surface OFZ is a defined volume of airspace along the sides of the runway and the inner-approach OFZ, and it applies only to precision instrument runways. The inner-transitional surface OFZ slopes 3 (horizontal) to 1 (vertical) out from the edges of the runway OFZ and the inner-approach OFZ to a height of 150 ft (50 m) above the established airport elevation. See also obstacle-limitation surfaces.
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved
References in periodicals archive ?
If the pilot observed the lights from the surrounding wind turbines, it is possible that he perceived a break in the light string between the wind turbines as an obstacle-free zone." The pilot was aware of the deteriorating weather before taking off, as evidenced by a weather briefing he obtained and statements made to a witness.
The obstacle-free zone of the precision approach and any under-run is there to protect you unless your gear hangs down like a stork.
The original plan called for travel lanes of 12 feet, paved shoulders of 10, and an obstacle-free zone of 30 feet, but after months of protests and frustrating meetings, Maine DOT has offered modest alterations.
Learn the basics of gliding, stopping, and turning in a traffic- and obstacle-free zone that is flat and free of cracks, twigs, or pebbles.
From top to bottom, the first three are: runway safety area/obstacle-free zone, beyond which you need to be cleared onto the runway: ILS-critical holding line/precision obstacle-free zone; holding position.