FAS | Nuke | Intro | Aircraft ||||| Index | Search |



Aviation Facilities

The general location of an aviation facility is governed by many factors, including base conversions, overall defense strategies, geographic advantages, mission realignment, security, and personnel recruitment. Site conditions must be considered when selecting a site for an aviation facility. The site considerations include, but are not limited to: topography, vegetative cover, existing construction, weather elements, wind direction, soil conditions, flood hazard, natural and man-made obstructions, adjacent land use, availability of usable airspace, accessibility of roads and utilities, and future expansion capability.

All facilities and functions directly involved in maintaining, servicing, controlling, and flying combat aircraft are considered related to ammunition and explosives on the flightline supporting those combat aircraft. Flightline related facilities and functions, which have in common, the need to directly support the same combat aircraft, can be considered integral parts of the aircraft generation; this also applies to “related” flightline munitions operating locations and pre-load areas. Because the combat aircraft generation cannot progress without their combined efforts, these flightline support functions and facilities may be considered “related” to each other, if they are considered “related” to the combat aircraft.

Aviation facilities typically are designed for a specific aircraft known as the "critical" or "design" aircraft, which is the most operationally and/or physically demanding aircraft to make substantial use of the facility. The critical or design aircraft is used to establish the dimensional requirements for safety parameters such as approach protection zones, lateral clearance for runways, taxiways and parking positions, and obstacle clearance. In many cases, the "geometric" design aircraft may not be the same aircraft as the "pavement" design aircraft.

Runways and Other Surfaces

Runways are attractive targets for enemy aircraft to take out. A bomb is dropped on a runway, which creates a large crater putting the runway out of commission. If aircraft can't get off the ground, then they can't fight. Rapid runway repair is a long, tedious process that is vital to success on the battlefield and in the skies. The main focus in airfield repair is the Minimum Operating Strip (MOS), which the United States doctrinally defines as 15 by 1,525 square meters for fighter aircraft and 26 by 2,134 square meters for cargo aircraft.

Take-off and landing areas are based on either a runway or helipad. The landing/take-off area consists not only of the runway and helipad surface, shoulders, and overruns, but also approach slope surfaces, safety clearances and other imaginary airspace surfaces. Aviation facilities normally have only one runway. Additional runways may be necessary to accommodate operational demands, minimize adverse wind conditions or overcome environmental impacts. A parallel runway may be provided based on operational requirements. Class A runways are primarily intended for small light aircraft. These runways do not have the potential or foreseeable requirement for development for use by high performance and large heavy aircraft. Ordinarily, these runways are less than 2,440 meters [8,000 feet] long and have less than 10 percent of their operations that involve aircraft in the Class B category. Class B runways are primarily intended for high performance and large heavy aircraft.

The capacity of a single runway system will vary from approximately 40 to 50 operations per hour under IFR conditions, up to 75 operations per hour under VFR conditions. Parallel runways are the most commonly used system for increased capacity. In some cases, parallel runways may be staggered with the runway ends offset from each other and with terminal or service facilities located between the runways. Where practical, parallel runway centerline separation of at least 5,000 feet (1 525 m) is recommended. Crosswind runways may be either the open-V or the intersecting type of runway. The crosswind system is adaptable to a wider variety of wind conditions than the parallel system. When winds are calm, both runways may be used simultaneously. An open-V system has a greater capacity than the intersecting system.

Runway overruns keep the probability of serious damage to an aircraft to a minimum in the event the aircraft runs off the runway during a take-off or lands short during a landing. Overruns are required for the landing and take-off area. Aircraft arresting systems consist of engaging devices and energy absorbers. Engaging devices are net barriers, disc supported pendants (hook cables), and cable support systems which allow the pendant to be raised to the battery position or retracted below the runway surface. Energy absorbing devices are ships anchor chains, rotary friction brakes, such as the BAK-9 and BAK-12, or rotary hydraulic systems such as the BAK-13 and E-28. The systems designated "Barrier, Arresting Kit" (BAK) are numbered in the sequence of procurement of the system design. There is no connection between the Air Force designations of these systems and their function.

Runways are identified by the whole number nearest one-tenth (1/10) the magnetic azimuth of the runway centerline. The magnetic azimuth of the runway centerline is measured clockwise from magnetic north when viewed from the direction of approach. For example, where the magnetic azimuth is 183 degrees, the runway designation marking would be 18; and for a magnetic azimuth of 117 degrees, the runway designation marking would be 12. For a magnetic azimuth ending in the number 5, such as 185 degrees, the runway designation marking can be either 18 or 19. Supplemental letters, where required for differentiation of parallel runways, are placed between the designation numbers and the threshold or threshold marking.

An alert pad, often referred to as an alert apron, is an exclusive paved area for armed aircraft to park and have immediate, unimpeded access to a runway. In the event of a declared alert, alert aircraft must be on the runway and airborne in short notice. Locating the alert pad adjacent to a runway end will allow alert aircraft to proceed directly from the apron to the runway threshold without interruptions from other traffic. Alert pads are located close to the runway threshold to allow alert aircraft to be airborne within the time constraints stipulated in their mission statements. The preferred location of alert pads is on the opposite side of the runway, away from normal traffic patterns to allow aircraft on the alert pad direct, unimpeded access to the runway.

A warm-up pad, also referred to as a holding apron, is a paved area adjacent to a taxiway at or near the end of a runway. The intent of a warm-up pad is to provide a parking location, off the taxiway, for aircraft which must hold due to indeterminate delays. It allows other departing aircraft unencumbered access to the runway. Typically the end cross over taxiway is widened to 46 m [150 ft] which provides room to accommodate aircraft warming up or waiting for other reasons. The most advantageous position for a warm-up pad is adjacent to the end turnoff taxiway, between the runway and parallel taxiway. However, other design considerations such as airspace and navigational aids may make this location undesirable. If airspace and navigational aids prevent locating the warm-up pad adjacent to the end turnoff taxiway, the warm-up pad should be located at the end of and adjacent to the parallel taxiway.

The arm/disarm pad is used for arming aircraft immediately before takeoff and for disarming (safing) weapons retained or not expended upon their return.

An aircraft compass calibration pad is a paved area in a magnetically quiet zone where an aircraft's compass is calibrated.

Hazardous cargo pads are paved areas for loading and unloading explosives and other hazardous cargo from aircraft. Hazardous cargo pads are required at facilities where the existing aprons cannot be used for loading and unloading hazardous cargo.

Taxiways provide for free ground movement to and from the runways, helipads, maintenance, cargo/passenger, and other areas of the aviation facility. The objective of taxiway system planning is to create a smooth traffic flow. This system allows unobstructed ground visibility; a minimum number of changes in the aircraft's taxiing speed; and, ideally, the shortest distance between the runways or helipads and apron areas. At airfields with high levels of activity, the capacity of the taxiway system can become the limiting operational factor. Runway capacity and access efficiency can be enhanced or improved by the installation of parallel taxiways. A full length parallel taxiway may be provided for a single runway with appropriate connecting lateral taxiways to permit rapid entrance and exit of traffic between the apron and the runway.

Aircraft parking aprons are the paved areas required for aircraft parking, loading, unloading, and servicing. They include the necessary maneuvering area for access and exit to parking positions. Aprons will be designed to permit safe and controlled movement of aircraft under their own power. Aircraft apron dimensions and size are based on mission requirements.

Support Structures and Facilities

Hangars provide space for various aircraft activities: scheduled inspections; landing gear tests; weighing of aircraft; major work and maintenance of fuel systems and airframes; and technical order compliance and modifications. These activities can be more effectively ccomplished while the aircraft is under complete cover. Pavement for hangar floors must be designed to support aircraft loads. Hangars provide covered floor space to accommodate aircraft. Clearance must be provided between the aircraft and the door opening, walls, and ceiling of the hangar.

The aircraft maintenance facility includes, but is not limited to: aircraft maintenance hangars, special purpose hangars, hangar access aprons, weapons system support shops, aircraft system testing and repair shops, aircraft parts storage, corrosion control facilities, and special purpose maintenance pads. The aircraft maintenance area includes utilities, roadways, fencing, and security facilities and lighting. Aircraft maintenance facilities are generally located on one side of the runway to allow simplified access among maintenance areas, aircraft, and support areas.

Aviation operations support facilities include those facilities that directly support the flying mission. Operations support includes air traffic control, aircraft rescue and firefighting, fueling facilities, airfield operations center (airfield management facility), squadron operations/aircraft maintenance units, and air mobility operations groups. Aviation operations support facilities are generally located along the hangar line with the central area typically being allocated to airfield operations (airfield management facility), air traffic control, aircraft rescue and firefighting, and flight simulation.

Aircraft fuel storage and dispensing facilities are provided at most aviation facilities. Operating fuel storage tanks are provided where dispensing facilities are remote from bulk storage. Bulk fuel storage areas require locations which are accessible by tanker-truck, tanker-rail car, or by waterfront. Both bulk storage and operating storage areas provide for the loading and parking of fuel vehicles to service aircraft. Where hydrant fueling systems are authorized, bulk fuel storage locations take into account systems design requirements (e.g., the distance from the fueling apron to the storage tanks). Fuel storage and operating areas have requirements for minimum clearances from buildings, aircraft parking, roadways, radar, and other structures/areas, as established in service directives. Aviation fuel storage and operating areas also require lighting, fencing, and security alarms. Liquid fuel storage facility sitings address spill containment and leak protection/detection.

Navigational Aids (NAVAIDS)

Navigational Aids (NAVAIDS) assist the pilot in flight and during landing. A lighting equipment vault is provided for airfields and heliport facilities with navigational aids, and may be required at remote or stand-alone landing sites. A (NAVAID) building will be provided for airfields with navigational aids. Each type of NAVAID equipment is usually housed in a separate facility.

The microwave landing system (MLS) provides the pilot of a properly equipped aircraft with electronic guidance to control the aircraft's alignment and descent until the runway environment is in sight. MLS is also used to define a missed approach course or a departure course. MLS is not particularly susceptible to signal interference as a result of buildings, trees, power lines, metal fences, and other large objects. However, when these objects are in the coverage area, they may cause multipath (signal reflection) or shadowing (signal blockage) problems. MLS antenna systems do not use the ground to form the desired signal. Grading for MLS installations is usually limited to that needed for the antenna and monitors, a service road, and a vehicle parking area.

The instrument landing system (ILS) provides pilots with electronic guidance for aircraft alignment, descent gradient, and position until visual contact confirms the runway alignment and location. The ILS uses a line-of-sight signal from the localizer antenna and marker beacons and a reflected signal from the ground plane in front of the glide slope antenna. ILS antenna systems are susceptible to signal interference sources such as power lines, fences, metal buildings, etc. Since ILS uses the ground in front of the glide slope antenna to develop the signal, this area should be graded to remove surface irregularities.

The non-directional beacon (NDB) radiates a signal which provides directional guidance to and from the transmitting antenna. An NDB is normally mounted on a 35 foot (11 m) pole. A NDB may be located on or adjacent to the airport. Metal buildings, power lines, or metal fences should be kept 100 feet (30 m) from a NDB antenna. Electronic equipment is housed in a small collocated shelter.

The standard very high frequency omnirange (VOR) located on an airport is known as a TVOR. TVORs radiate azimuth information for nonprecision instrument approach procedures. If the airport has intersecting runways, TVORs should be located adjacent to the intersection to provide approach guidance to both. TVORs should be located at least 500 feet (150 m) from the centerline of any runway and 250 feet (75 m) from the centerline of any taxiway. TVOR sites should be level within 1000 feet (300 m) of the antenna. However, a downward slope of as much as 4 percent is permitted between 200 feet (60 m) and 1,000 feet (300 m) of the antenna.

From airport traffic control towers (ATCTs), ATC personnel control flight operations within the airport's designated airspace and the operation of aircraft and vehicles on the movement area. A typical ATCT site will range from 1 to 4 acres (0.4 to 1.6 hectares). Additional land may be needed for combined flight service stations/towers.

Airport surveillance radars (ASR) are used to control air traffic. ASR antennas scan through 360 degrees to present the controller with the location of all aircraft within 60 nautical miles of the airport. The site for the ASR antenna is flexible. The ASR antenna should be located as close to the ATCT control room as practical. Antennas should be located at least 1,500 feet (450 m) from any building or object that might cause signal reflections and at least one-half mile (.8 km) from other electronic equipment. ASR antennas may be elevated to obtain line-of-sight clearance. Typical ASRs heights range from 25 to 85 feet (7.5 to 25.5 m) above ground.

Airport surface detection equipment (ASDE) compensates for the loss of line of sight to surface traffic during periods of reduced visibility. ASDE should be sited to provide line-of-sight coverage of the entire aircraft movement area. While the ideal location for the ASDE antenna is on the ATCT cab roof, the antenna may be placed on a freestanding tower up to 100 feet (30 m) tall located within 6,000 feet (1 800 m) of the ATCT cab.

Hardened Facilities

If dispersal of aircraft is possible and consistent with active defense measures, varied parking patterns provide fewer lucrative targets for indirect-fire weapons. Prefabricated, hard parking surfaces such as landing mats increase lethal areas of bursting rounds due to induced fragmentation. Effects of other hardened surfaces, such as bituminous materials and concrete, are unknown but probably increase fragment success as well. Reduced damage from indirect-fire attacks should result when parking areas can be adequately maintained on sod or on a surface that does not cause fragment ricochet.

The violent release of energy from a detonation in a gaseous medium results in a sudden pressure increase in that medium. The pressure disturbance, termed the blast wave or overpressure, is characterized by an almost instantaneous rise from the ambient pressure to a peak incident pressure (Pso). This pressure increase, or shock front, travels radially from the burst point with a diminishing velocity that always is in excess of the sonic velocity of the medium. Gas molecules making up the front move at lower velocities. This latter particle velocity is associated with a "dynamic pressure," or the pressure formed by the winds produced by the shock front. As the shock front expands into increasingly larger volumes of the medium, the peak incident pressure at the shock front decreases and the duration of the pressure increases. If the shock wave impinges on a rigid surface, oriented perpendicular to or at an angle to the direction of propagation of the wave, an additional reflected pressure instantly is developed on that rigid surface and the pressure is raised to a value that exceeds the incident pressure. This additional reflected pressure is (from that moment on) a function of the cumulative pressure in the incident wave and the pressure induced by the angle formed between the rigid surface and the plane of the initial shock front.

When an explosion occurs within a structure, the peak pressure associated with the initial shock front will be extremely high, and in turn, may be amplified by its reflections with hardened surfaces in the structure. In addition, the accumulation of gases from the explosion will exert additional pressures and increase the load duration within the structure. The combined effects of these pressures may actually destroy the unreinforced structure because adequate venting for the expanding gas and the reflected shock pressures were not provided for in the original facility design analysis. For structures that have one or more strengthened walls, venting for relief of excessive gas or shock pressures, or both, may be provided by means of openings in or frangible construction of the facility walls or roof, or both. This type of construction will permit the blast wave from an internal explosion to spill over onto the exterior ground and building surfaces. These pressures (referred to as exterior or leakage pressures), once released from their confinement, expand radially and act near instantaneously on nearby structures or persons on the other side of the barrier.

An important consideration in the analysis of the hazard associated with an accidental explosion is the effect of fragments generated by the explosion. These fragments are classified as primary or secondary depending on their origin.Primary fragments are formed as a result of the shattering of the explosives container. The container may be the casing of conventional munitions, the kettles, hoppers, and other metal containers used in the manufacture of explosives; the metal housing of rocket engines; and similar items. These fragments usually are small in size and travel initially at velocities of the order of thousands of feet per second. Secondary fragments are formed as a result of high blast pressures on structural components and items in close proximity to the explosion. These fragments are somewhat larger in size than primary fragments and travel initially at velocities in the order of hundreds of feet per second. A hazardous (life threatening) fragment is one having an impact energy of 58 ft-lb (79 joules) or greater.

Barricades, if properly designed and located, stop fragments. A barricade at the source can reduce fragment speed and density where high-density exposures of personnel and equipment may occur. A secondary barricade at sites of mission-essential equipment and personnel (such as wing communications and trim pads) can provide some additional protection; however, high-angle, low-velocity fragments will still impact the exposed site. Earth-Filled, Steel-Bin-Type Barricades (ARMCO, Republic type, or equal) will prevent simultaneous detonation of adjacent explosives; however, they will not prevent major damage or destruction of aircraft or munitions.

Revetments are barricades constructed to limit or direct a blast to reduce damages from low flying fragments and limit simultaneous detonation. Often used to form modules for open storage of munitions or protected aircraft parking. A module is a barricaded area comprised of a series of connected cells with hard surface storage pads separated from each other by barricades. A light metal shed or other lightweight fire retardant cover may be used for weather protection for individual cells.

Thin-walled revetments have been developed for protection of attack, utility, and cargo-type helicopters. These revetments have plywood or corrugated metal walls and contain 12 inches of soil fill. Thin-walled revetments may be post-supported or freestanding. Post-supported revetments use either timber or pipe posts and are designed primarily for protection of cargo-type helicopters. Freestanding revetments are designed for protection of utility and attack helicopters. They provide protection from fragmentation of near misses (10 meters) from mortars and artillery rounds up to 155 millimeters. Thin-walled revetments (12 inches thick) require less fill material, space, equipment, and construction time than thick-walled revetments (4 feet or more).

Revetments constructed with filled sandbags are a practical expedient for fortifications, particularly when equipment is limited to hand tools or when skilled personnel are not available to supervise the construction of other types of protective structures. Fill the bags at the construction site with sand hauled to the location. The bags also can be filled where the sand is available and hauled to the site; however, this procedure is less preferable because the bags may be damaged during handling. A disadvantage of sandbag revetments is that the bags deteriorate rapidly, particularly in damp climates. Thus, the filler material may run out, reducing the protective characteristics and endangering the stability of the revetment. Shell hits may require replacement of bags.

Aircraft in closed Hardened Aircraft Shelters (HAS) will remain operable should an explosion occur in an adjacent shelter or ready service storage facility. However, adjacent structures, aircraft and stored munitions may be substantially damaged or destroyed. These aircraft may not be immediately removable due to debris. For shelters with third generation-type rear doors, the aircraft may be damaged substantially unless modifications have been made to prevent the rear doors from being blown against the aircraft.

Barricaded open-storage modules provide a high degree of protection against propagation of explosion by blast and fragments. However, if flammable materials are present in nearby cells, subsequent propagation of explosion by fire is possible. In the event of an unplanned detonation in an adjacent cell, munitions may be covered with earth and unavailable for use until extensive uncovering operations and possibly maintenance are completed.

An Explosives Storage Area is a designated area of explosives-containing facilities set aside for the exclusive storage or "warehousing" of the base explosives stocks. Facilities include igloos, magazines, operating buildings, modules, revetments, and outdoors storage sites. Magazines are of two general types: igloo (earth-covered) and aboveground (no earth covering). An aboveground magazine is any structure or facility, without sufficient earth covering, used for the storage of explosives.

Earth-covered magazines (igloo or underground) are preferred for the storage of all explosives. Priority is given to covered storage (igloos) for items requiring protection from the elements or long term storage. Igloo magazines are used to store all types of explosives and are preferred for mass detonating explosives where moisture condensation is not a problem. They are earth-covered, and are either of a concrete or steel arch-type construction. The steel arch type is normally more economical to construct than the reinforced concrete igloo. This is especially true where the cost of additional land area and connecting road net required to construct a multiple igloo complex is considered. The steel arch-earth covered igloo has a concrete floor, foundations, side arches, and a rear and front wall. It may be constructed in variable lengths in 0.6 m (2 ft) increments and in widths up to 9.1 m (30 ft ). The arch is constructed of heavy gauge corrugated steel plates, and the double leaf doors are of heavy blast resistant steel.

The primary objective of an earth-covered magazine is to provide protection for its assets. Substantial deformation of the magazine may occur, however, the stored assets should be protected. Earth-covered magazines provide virtually complete protection against propagation of explosions by blast, fragments, and fire; however, there may be structural failures in the magazines’ concrete barrels and walls, possible severe damage of front walls, and damage to doors and ventilators. Munitions assets are expected to remain serviceable following an explosion in an adjacent earth covered magazine. The earth-covered magazines types are defined by the effects on the head wall and blast door hardness. All earth-covered magazines have the same earth-cover requirements. The earth cover over an igloo magazine will normally be at least 2 feet deep. Lightning protection systems feature air terminals, low impedance paths to ground, sideflash protection, surge suppression of all conductive penetrations into the protected area, and earth electrode systems. Structural elements of the building may serve as air terminals, down conductors, or the earth electrode. For air terminals to be omitted on earth covered igloos the reinforcing bars or steel arch must be electrically bonded between structural elements and connected to the grounding system.

Sources and Methods



FAS | Nuke | Intro | Aircraft ||||| Index | Search |


http://www.fas.org/nuke/intro/aircraft/facilities.htm

Maintained by Webmaster
Updated Wednesday, June 28, 2000 1:29:49 PM