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39-429: At some airfields, the airport/aerodrome beacon may also be ARCAL controlled. ARCAL is most common at non-towered airports or little-used airfields where it is neither economical to light the runways all night, nor to provide staff to turn the runway lighting on and off. It enables pilots to control the lighting only when required, saving electricity and reducing light pollution. The ARCAL frequency for most aerodromes

78-460: A mode C veil , which encompasses airspace within thirty nautical miles of the airport. Aircraft operating within the Mode C veil must have an operating Mode C transponder (up to 10,000 feet (3,000 m) MSL) unless the aircraft is certified without an engine-driven electrical system, operates outside the class B, below the ceiling of the class B and below 10,000 feet (3,000 m) MSL. Class C space

117-420: A five-second period to determine pilot intent. The pilot commanded output is held by the controller for a predetermined time interval ( Federal Aviation Administration standard is 15 minutes) that is generally adjustable. The five-second click count period begins upon receipt of the first squelch break and the control sequence will respond to the click counts from three, five, seven and stop. As an example, cycling

156-699: A frequency of 20 to 30 flashes per minute. Heliports with beacons exhibit the morse letter H (4 short flashes) at a rate of 3 to 4 groups per minute. Airspace class (United States) The United States airspace system's classification scheme is intended to maximize pilot flexibility within acceptable levels of risk appropriate to the type of operation and traffic density within that class of airspace – in particular to provide separation and active control in areas of dense or high-speed flight operations. The Albert Roper (1919-10-13 The Paris Convention) implementation of International Civil Aviation Organization (ICAO) airspace classes defines classes A through G (with

195-481: A standardized altimeter setting of 29.92" InHg and thus the true altitudes depend on local atmospheric pressure variations. Unless otherwise authorized by ATC, all flight operations in class A airspace must be under ATC control, and must be operating IFR, under a clearance received prior to entry. An example of an exception to IFR-only flight in this airspace is the use of wave windows . These specific airspace blocks may be opened by ATC to allow sailplanes to fly in

234-447: Is 500 ft below, 1,000 ft above, 2,000 ft horizontal; at or above 10,000 ft MSL, they are 1,000 ft below, 1,000 ft above, and 1 mile laterally. By day at 1,200 feet (370 m) AGL and below, aircraft must remain clear of clouds, and there is no minimum lateral distance. There are certain exceptions where class G extends above 1,200 feet AGL. This is usually either over mountainous terrain (e.g., some areas in

273-411: Is a beacon installed at an airport or aerodrome to indicate its location to aircraft pilots at night. An aerodrome beacon is mounted on top of a towering structure, often a control tower , above other buildings of the airport. It produces flashes similar to that of a lighthouse . Airport and heliport beacons are designed in such a way to make them most effective from one to ten degrees above

312-489: Is found still controls the requirements and procedures for flying into/through it. Alert areas are depicted on aeronautical charts to inform non-participating pilots of areas that may contain a high volume of pilot training or an unusual type of aerial activity. Pilots should be particularly alert when flying in these areas. All activity within an alert area must be conducted in accordance with CFRs, without waiver, and pilots of participating aircraft as well as pilots transiting

351-407: Is in effect only during the hours of tower and approach operation at the primary airport; the airspace reverts to Class D if approach control is not operating, and to class E or G if the tower is closed. The vertical boundary is usually 4,000 feet (1,200 m) above the airport surface. The core surface area has a radius of five nautical miles (9 km), and goes from the surface to the ceiling of

390-418: Is no regulation requiring daytime operation. At some locations with operating control towers, ATC personnel turn the beacon on or off with controls in the tower. At many airports the airport beacon is turned on by a photoelectric cell or time clocks, and ATC personnel cannot control them. In Canada, the regulations are different. Lighted aerodromes are equipped with white single flash beacons operating at

429-497: Is no scheduled commercial passenger service). Class D airspace is generally cylindrical in form and normally extends from the surface to 2,500 feet (760 m) above the ground. Airspace within the given radius, but in surrounding class C or class B airspace, is excluded. Class D airspace reverts to class E or G during hours when the tower is closed, or under other special conditions. Two-way communication with ATC must be established before entering class D airspace, but no transponder

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468-440: Is no specific pilot certification required. Aircraft speeds must be below 200 knots (230 mph) at or below 2,500 feet (760 m) above the ground, and within 4 nautical miles (7 km) of the class C airport. Class D airspace is typically established around any airport with a functioning control tower, but that does not see significant IFR approaches which would make Class B or C more appropriate (usually because there

507-630: Is not required; however, the controller of Class C space may instruct aircraft initiating communication to "remain outside" the airspace. The aircraft must be equipped with a two-way radio and an operating Mode C (altitude reporting) radar transponder, furthermore aircraft overflying above the upper limit of class C airspace upward to 10,000 feet MSL must have an operating Mode C transponder. VFR flights in class C airspace must have three miles (5 km) of visibility, and fly an altitude at least 500 feet (150 m) below, 1,000 feet (300 m) above, and 2,000 feet (600 m) laterally from clouds . There

546-536: Is not used in the U.S. Besides controlled and uncontrolled airspace, other types of airspace include "special use" and "other airspace". Class A airspace extends from 18,000 feet (5,500 m) mean sea level MSL to FL600 (approximately 60,000 feet (18,000 m) MSL) throughout the contiguous United States and Alaska. Unlike the altitude measurements used in other airspace classes, the FLnnn flight levels used in class A airspace are pressure altitudes referenced to

585-475: Is required. VFR cloud clearance and visibility requirements are the same as class C. Controlled airspace which is neither class A, B, C nor D. In most areas of the United States, class E airspace extends from 1,200 feet (370 m) above ground level (AGL) up to but not including 18,000 feet (5,500 m) MSL, the lower limit of class A airspace. There are areas where class E airspace begins at either

624-429: Is strongly recommended that aircraft on final approach to the airfield issue a fresh lighting command, even if the lights are already on, especially if the lights were activated by another aircraft. This is so that the lighting does not turn off at a critical moment, such as when crossing the runway threshold. When in operation, the receiver awaits a squelch break on the tuned VHF frequency and begins counting "clicks" in

663-473: Is structured in much the same way as class B airspace, but on a smaller scale. Class C airspace is defined around airports of moderate importance; airports with regular commercial passenger jet service of 100 passengers per flight or more are typically Class C. The FAA requirements for Class C airspace status are an operational control tower , a radar-controlled approach system, and a minimum number of IFR approaches conducted per year. The airspace class designation

702-445: Is to warn non-participating pilots of the potential danger. A warning area may be located over domestic or international waters or both. Entry into restricted areas is prohibited under certain conditions without a special clearance obtained from the controlling agency obtained directly or via ATC. Examples of restricted areas include test firing ranges and other military areas with special hazards or containing sensitive zones (such as

741-623: Is typically the airspace very near the ground (1,200 feet or less), beneath class E airspace and between class B-D cylinders around towered airstrips. Radio communication is not required in class G airspace, even for IFR operations. Class G is completely uncontrolled. VFR visibility requirements in class G airspace are 1 mile (1.6 km) by day, and 3 miles (5 km) by night, for altitudes below 10,000 feet (3,050 m) MSL but above 1,200 ft AGL. Beginning at 10,000 feet MSL, 5 miles (8 km) of visibility are required, day and night. Cloud clearance requirements are to maintain an altitude that

780-678: Is usually the same as the UNICOM / CTAF frequency, although in some rare cases, a second ARCAL frequency may be designated to control the lighting for a second runway separately. An example of the latter is runway 18/36 at the airport in Sydney, Nova Scotia . To activate the lights, the pilot clicks the radio transmit switch on the ARCAL frequency a certain number of times within a specified number of seconds. There are two types of ARCAL systems — type J and type K. Type J systems are activated by keying

819-768: The Rocky Mountains ), or over very sparsely populated areas (e.g., some parts of Montana and Alaska ). · Above FL600 (PPL required at some Class B) · 500' below · 2,000' horizontally · 500' below · 2,000' horizontally · 500' below · 2,000' horizontally · 1,000' below · 1 SM horizontally · 500' below · 2,000' horizontally · 500' below · 2,000' horizontally · 500' below · 2,000' horizontally · 1,000' below · 1 SM horizontally · < 250 KIAS while below 10,000' MSL Some airspace categories have no correlation with ICAO airspace classes but are nevertheless important in United States airspace. The airspace class (A, B, etc.) in which special use airspace

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858-482: The lee waves of mountains. Since class A airspace is normally restricted to instrument flight only, there are no minimum visibility requirements. Class A airspace was formerly known as Positive Control Airspace (PCA). Class B airspace is defined around key airport traffic areas, usually airspace surrounding the busiest airports in the US according to the number of IFR operations and passengers served. The exact shape of

897-577: The airport. Many class B airspaces diverge from this model to accommodate traffic patterns or local topological or other features. The upper limit of class B airspace is normally 10,000 feet (3,000 m) MSL. All aircraft entering class B airspace must obtain ATC clearance prior to entry and must be prepared for denial of clearance. Aircraft must be equipped with a two-way radio for communications with ATC, an operating Mode C transponder and automatic altitude reporting equipment. Furthermore, aircraft overflying

936-483: The airspace varies from one class B area to another, but in most cases it has the shape of an inverted wedding cake, with a series of circular "shelves" of airspace of several thousand feet in thickness centered on a specific airport. Each shelf is larger than the one beneath it. Class B airspace normally begins at the surface in the immediate area of the airport, and successive shelves of greater and greater radius begin at higher and higher altitudes at greater distances from

975-400: The area must be equally responsible for collision avoidance. Alert areas contain special hazards that pilots must take into consideration when entering the areas. A warning area is airspace of defined dimensions, extending from three nautical miles outward from the coast of the U.S., that contains activity that may be hazardous to non-participating aircraft. The purpose of such warning areas

1014-402: The class B airspace). VFR flights operating in class B airspace must have three miles (5 km) of visibility and must remain clear of clouds (no minimum distance). Class B airspace has the most stringent rules of all the airspaces in the United States. Class B has strict rules on pilot certification. Pilots operating in class B airspace must have a private pilot's certificate, or have met

1053-406: The class C airspace. The upper "shelf" area has a radius of ten nautical miles, and extends from as low as 1,200 feet (370 m) up to the ceiling of the airspace. A procedural "outer area" (not to be confused with the shelf area) has a radius of 20 nautical miles. All aircraft entering class C airspace must establish two-way radio communication with ATC prior to entry; explicit clearance to enter

1092-464: The exception of class F which is not used in the United States). The other U.S. implementations are described below. The United States also defines categories of airspace that may overlap with classes of airspace. Classes of airspace are mutually exclusive. Thus, airspace can be "class E" and "restricted" at the same time, but it cannot be both "class E" and "class B" at the same location and at

1131-419: The following rules for airport beacons: Flashing rates Color combinations In Class B, C, D, and E surface areas, operation of the airport beacon between sunrise and sunset often indicates that the ground visibility is less than 3 miles and/or the ceiling is less than 1,000 feet. This is true particularly at locations where beacon controls are available to air traffic control personnel; however there

1170-512: The horizon; however, they can be seen well above and below this peak spread. The beacon may be an omnidirectional flashing xenon strobe , or it may be an aerobeacon rotating at a constant speed which produces the visual effect of flashes at regular intervals. Flashes may be of one, two, or three alternating colors ( described below ). In the United States, the Federal Aviation Administration (FAA) has established

1209-572: The microphone button rapidly 15 times in five seconds will command "three, five, seven". Similarly, slowly clicking seven times may result in the five-second timing period expiring prior to getting to the seventh input click. In the United States, pilot-controlled lighting is governed by Federal Communications Commission Rule 87.187y. This section also lists the radio frequencies that are allowed to control runway lights via pilot-controlled lighting. Aerodrome beacon An aerodrome beacon , airport beacon , rotating beacon or aeronautical beacon

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1248-427: The microphone five times within five seconds, while type K is initially activated by clicking seven times within five seconds. Once activated, the intensity of type K systems may then be turned to low, medium, or high intensity settings by keying the microphone three, five, or seven times within five seconds, respectively. If runway identification lights are also controlled by type K ARCAL, they may be turned off by keying

1287-444: The microphone three times. When either type of system is activated, a 15-minute countdown starts, after which the lights turn off. While the lights are on, whenever a lighting command is issued, whether it changes the lighting intensity or not, the fifteen-minute countdown is reset. At some airfields, the lights may flash once to warn pilots that the lights are about to go off, before turning off two minutes later. When using ARCAL, it

1326-665: The one over Groom Lake ). Entry into prohibited areas is forbidden under all circumstances, except for an emergency, and the only aircraft that can access such specific areas are military aircraft with extremely special clearance, such as Marine One landing on the White House 's South Lawn . Prohibited areas exist over a handful of extremely sensitive locations, such as the White House , National Wildlife Refuge , Boundary Waters Canoe Area Wilderness and The National Mall . Military operation areas (MOA) are areas in which military activities are regularly conducted. No clearance

1365-476: The requirement of 14 CFR 61.95. These are often interpreted to mean "have an instructor's endorsement for having been properly trained in that specific class B space". However, it does not apply to student pilots seeking sport or recreational certificates. Some class B airports (within class B airspaces) prohibit student pilots from taking off and landing there. In addition to this, some class B airspaces prohibit special VFR flights. Certain class B airports have

1404-550: The same as for class C and D airspaces when below 10,000 feet (3,000 m) MSL. Above 10,000 ft MSL, the visibility requirement is extended to 5 miles (8 km) and the cloud clearance requirement is extended to 1,000 feet (300 m) below clouds, 1,000 feet (300 m) above, and 1 mile (1.6 km) laterally. Class G airspace includes all airspace below 14,500 feet (4,400 m) MSL not otherwise classified as controlled. There are no entry or clearance requirements for class G airspace, even for IFR operations. Class G airspace

1443-436: The same time. Note: All airspace classes except class G require air traffic control (ATC) clearance for instrument flight rules (IFR) operations. In the U.S., airspace is categorized as regulatory and non-regulatory. Within these categories exist: controlled (classes A, B, C, D, and E) and uncontrolled (class G) airspace, based on which air traffic control service is provided to IFR flights and some VFR flights. Class F

1482-424: The surface (SFC) or 700 AGL, these areas are used to transition between the terminal and en-route environments (around non-towered airports ). These areas are designated on sectional charts . Most airspace in the United States is class E. The airspace above FL600 is also class E. No ATC clearance or radio communication is required for VFR flight in class E airspace. VFR visibility and cloud clearance requirements are

1521-525: The upper limit of any class B airspace must have an operating Mode C transponder. Visual flight rules (VFR) flights may proceed under their own navigation after obtaining clearance but must obey any explicit instructions given by ATC. Some class B airspaces include special transition routes for VFR flight that require communication with ATC but may not require an explicit clearance. Other class B airspaces include VFR corridors through which VFR flights may pass without clearance (and without technically entering

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