空域クラスの説明（クラスA、B、C、D、E、G）

Airspace Classes Explained (Class A, B, C, D, E, G) - Pilot Institute Airspace Classes What Is an Airspace Class? Controlled and Uncontrolled Airspace Class A Airspace Class B Airspace Class C Airspace Class D Airspace Class E Airspace Class G Airspace Special Use Airspace Restricted Areas Prohibited Areas Warning Areas Military Operation Areas (MOAs) Alert Areas National Security Areas (NSAs) Other Airspace Areas Temporary Flight Restrictions (TFRs) Air Defense Identification Zone (ADIZ) Military Training Routes (MTRs) VFR Flyway VFR Transition Routes Terminal Radar Service Areas (TRSA) Special Flight Rules Areas (SFRAs) Special Air Traffic Rules Areas (SATRs) Conclusion Ever feel confused about the complex definitions of airspace? You’re not alone. Without a solid understanding of the different types of airspace, you risk an awkward conversation with ATC at best and a trip to court at worst. Let’s make sure that doesn’t happen to you. In this article, we’ll cover everything you need to know about airspace in the US. Airspace Classes What Is an Airspace Class? A class is a type of airspace. The Federal Aviation Administration (FAA) defines classes using letters like A or B. The needs of the airspace determine which class to use. For example, Phoenix’s bustling Sky Harbor International Airport has a high volume of airliner traffic. The custom-made Class B airspace keeps the busy operations moving safely. Nearby Casa Grande Municipal Airport is much smaller and has no airliner operations. Class G airspace works well for this airport’s more basic needs. But what do these classes mean? Let’s find out. Controlled and Uncontrolled Airspace A class of airspace is either controlled or uncontrolled . Controlled airspace is where air traffic control (ATC) has the authority to control traffic. In uncontrolled airspace, they don’t. Any guidance ATC gives pilots in uncontrolled airspace is advisory only. Classes A, B, C, D, and E are controlled airspace. Class G is the only uncontrolled airspace class. First, let’s explain controlled airspace, starting with Class A. Class A Airspace Class A airspace is all around the United States, beginning at 18,000 feet Mean Sea Level (MSL) and going to 60,000 feet MSL. Since Class A airspace is everywhere, sectional charts don’t depict it. Aircraft in Class A airspace don’t use feet to express altitude. Instead, they use flight levels . A flight level is pressure altitude expressed in hundreds of feet. For example, 20,000 feet MSL would be flight level 200 (FL200). All aircraft use the same altimeter setting of 29.92 inches of mercury. This helps aircraft maintain good vertical separation despite local variations in pressure. Class A airspace is instrument flight rules (IFR) only. You must be on an instrument flight plan and cleared by ATC to enter. You will need a two-way radio, Mode-C transponder, and ADS-B Out. If navigating via VORs above flight level 240, you need distance measuring equipment (DME) or GPS. The speed limit in Class A airspace is Mach 1. Class B Airspace You will find Class B airspace around the nation’s 37 busiest airports in major cities. If you could see Class B airspace in 3D, it would look like an upside-down wedding cake. This is because it consists of several tiers with different altitudes and shapes. Each Class B airspace is custom-made for the airport it surrounds. Sectional charts depict Class B airspace with solid blue lines. Each sector has an altitude block with a floor and ceiling . The floor is where the airspace starts, and the ceiling is where it ends. The chart lists these in hundreds of feet MSL with a line in between. The inner sector of Class B airspace starts at the airport surface (indicated by “SFC”). It extends up to around 10,000 feet MSL. Sectors further out will have higher bases, allowing traffic to fly underneath. A 30-nautical mile Mode C veil surrounds Class B airspace. The sectional chart depicts this boundary as a magenta circle. Inside the circle, all aircraft need an operating Mode-C transponder and ADS-B Out. The VFR weather minimums require at least 3 statute miles of visibility. The only cloud distance requirement is to stay clear of clouds. If you’re flying in Class B airspace that starts at the surface, the cloud ceiling must be at least 1,000 feet AGL . There’s also a speed limit of 200 knots below Class B and through its VFR corridors. Before entering Class B Airspace, VFR aircraft must receive clearance from ATC. Class C Airspace Class C airspace exists at large airports that are less busy than Class B airports. You will find them around most medium-sized to large cities. On the sectional chart, Class C airspace looks similar to Class B airspace, only it’s smaller. It also has magenta lines instead of blue. The inner core extends from the airport surface to around 4,000 feet AGL and has a radius of 5 nautical miles. The outer shelf has a radius of 10 nautical miles. It starts at 1,200 feet AGL and also extends to 4,000 feet AGL. Flying VFR in Class C airspace requires at least 3 statute miles of visibility. Traffic separation isn’t as tightly controlled as in Class B airspace. You’ll need to fly further from clouds to help see and avoid other aircraft. You must fly at least 1,000 feet above, 500 feet below, and 2,000 feet horizontally from clouds. The speed limit is 200 knots within a 4-nautical mile radius of the airport. Otherwise, the standard limit of 250 knots below 10,000 feet MSL applies. You don’t need ATC clearance to enter Class C airspace. But, you must establish two-way radio communication first. The approach control frequency is in a white box with a magenta border on your sectional chart. You will need a Mode-C transponder and ADS-B Out to fly in or over Class C airspace. Class D Airspace You’ll find Class D airspace at airports that are busy enough to have a control tower but not as busy as Class C airspace. The sectional chart depicts Class D airspace with dashed blue lines. The number in the box indicates the ceiling in hundreds of feet MSL. A minus sign indicates the airspace ceiling goes up to but doesn’t include the listed altitude. Class D airspace resembles a cylinder with a radius of about 4 or 5 nautical miles. It starts from the airport surface and extends to about 2,500 feet AGL or the airspace floor above it. The VFR weather minimums are the same as Class C airspace. You need 3 statute miles visibility, and you must stay 1,000 feet above, 500 feet below, and 2,000 feet horizontally from clouds. Since the airspace is small and doesn’t extend far from the airport, the speed limit is 200 knots. Before entering Class D airspace, you must establish two-way radio communications with the tower. Part-Time Class D Airspace It’s common for control towers at Class D airports to close at night when traffic is slow. Sectional charts identify these part-time control towers with a “*” beside the tower frequency. You’ll find the hours of operation in the Chart Supplement. When the tower shuts down, the Class D airspace no longer exists. What airspace goes in its place? It depends on whether the airport meets weather reporting and communications requirements. If the airport meets requirements, it becomes surface Class E airspace. It reverts to Class G airspace if it can’t meet those requirements. Class E Airspace Any controlled airspace that is not Class A, B, C, or D is Class E. Class E airspace fills in the gaps. It allows ATC to manage IFR aircraft outside other controlled airspace. In most of the country, Class E airspace starts at 1,200 feet AGL, 700 feet AGL, or the surface. Unless the chart indicates otherwise, you can assume Class E airspace always begins at 1,200 feet AGL. But how do we know where it starts lower? Look for shaded magenta shapes on a sectional chart. The FAA calls these vignettes . They depict changes in the floor of Class E airspace. On the “faded” side of the magenta vignette, the floor starts at 700 feet AGL. These are transition areas . They allow ATC to provide services to IFR aircraft flying in or out of airports. These are particularly useful at airports without a control tower. On the “solid” side of the shaded area, Class E starts at 1,200 feet AGL. You might see a dashed magenta ring inside these transition areas around an airport. This ring indicates that the Class E airspace goes down to the ground. Remember when we said that Class E starts at 1,200 feet at the highest in most of the country? Although rare, places exist where Class E starts at 14,500 feet MSL. You will see this represented by a blue vignette. The “faded” side of the vignette represents the typical floor of 1,200 feet AGL. The “solid” side represents a floor of 14,500 feet MSL. Class E airspace extends up to, but doesn’t include, the floor of Class A airspace at 18,000 feet. It starts again after Class A ends at 60,000 feet and continues to the end of the atmosphere. Even SR-71 pilots can’t avoid Class E airspace! Aircraft operating under VFR are not required to maintain radio communications with ATC. There are no Class E entry requirements. But, there are VFR weather minimums. If you’re below 10,000 feet MSL, the weather minimums are the same as Class C and D airspace. You need 3 statute miles visibility, and you must stay 1,000 feet above, 500 feet below, and 2,000 feet horizontally from clouds. If you’re above 10,000 feet, the minimums increase to 5 statute miles visibility. You need to stay 1,000 feet above, 1,000 feet below, and 1 statute mile horizontally from clouds. Class G Airspace Class G airspace is uncontrolled airspace. It exists wherever controlled airspace doesn’t . Class G starts at the surface unless controlled airspace exists on the ground. You won’t find Class G airspace depicted on the sectional chart, and there are no entry or communication requirements. Class G VFR weather minimums are somewhat complicated. If you’re in Class G under 10,000 feet MSL, you need 1 statute mile of visibility