Airspace Preview

United States airspace has six classes, named by letter: A, B, C, D, E, and G. There is no Class F in the United States. Each point in the sky is in exactly one class. Special use areas lie inside the classes with their own names and their own rules. The Pilot's Handbook states the categories: "The two categories of airspace are: regulatory and nonregulatory. Within these two categories, there are four types: controlled, uncontrolled, special use, and other airspace" 1. The AIM lists the same four types and places three kinds of airspace on the regulatory side 2:

• Classes A through E
• restricted areas
• prohibited areas.

The order of the letters

The letters are in order from the most controlled to the least controlled. Class A is the most restrictive, and "all operation in Class A airspace is conducted under instrument flight rules" 3. Class G is uncontrolled: "the portion of the airspace that has not been designated as Class A, B, C, D, or E" 4. Between them, each letter has more requirements for a pilot than the letter after it. A pilot who knows the letter of the airspace ahead knows what the rules require there.

What "controlled" means

Controlled airspace is airspace where air traffic control services and IFR separation exist. The Chart Users' Guide: "Controlled airspace consists of those areas where some or all aircraft may be subject to air traffic control, such as: Class A, Class B, Class C, Class D, Class E Surface (SFC) and Class E Airspace" 5. The word does not mean a VFR pilot needs permission everywhere in it. A VFR pilot flies most Class E with no radio call. ATC has no authority in Class G, and the handbook adds that "pilots should remember there are visual flight rules (VFR) minimums that apply to Class G airspace" 4. Three subjects for each class come later in the program:

• the entry requirements
• the equipment
• the weather minimums.

Class A is the airspace from 18,000 feet MSL to FL 600. The AIM: "Generally, that airspace from 18,000 feet MSL up to and including FL 600, including the airspace overlying the waters within 12 nautical miles off the coast of the 48 contiguous States and Alaska." All flight in Class A is IFR. The AIM adds: "Class A airspace is not specifically charted" 6. The sectional omits Class A because Class A fills the sky from 18,000 feet MSL up to FL 600. A Warrior never enters Class A.

Class B

Class B surrounds the busiest airports. The handbook: "Class B airspace is generally airspace from the surface to 10,000 feet MSL surrounding the nation's busiest airports in terms of airport operations or passenger enplanements. The configuration of each Class B airspace area is individually tailored, consists of a surface area and two or more layers (some Class B airspace areas resemble upside-down wedding cakes)." A pilot needs a clearance to enter: "ATC clearance is required for all aircraft to operate in the area" 7. The sectional shows Class B in solid blue. The Chart Users' Guide: "The MSL ceiling and floor altitudes of each sector are shown in solid blue figures with the last two zeros omitted" 5. A "100" over "30" on a blue line means a layer from 3,000 to 10,000 feet MSL.

Class C surrounds busy airports with a radar approach control. The handbook: "Class C airspace is generally airspace from the surface to 4,000 feet above the airport elevation (charted in MSL) surrounding those airports that have an operational control tower, are serviced by a radar approach control, and have a certain number of IFR operations or passenger enplanements." The shape is usually "a surface area with a five NM radius, an outer circle with a ten NM radius that extends from 1,200 feet to 4,000 feet above the airport elevation" 8. On the chart, Class C is solid magenta: "The MSL ceiling and floor altitudes of each sector are shown in solid magenta figures with the last two zeros eliminated" 5.

Class D

Class D surrounds smaller airports with an operating control tower. The handbook: "Class D airspace is generally airspace from the surface to 2,500 feet above the airport elevation (charted in MSL) surrounding those airports that have an operational control tower" 9. On the chart, "Class D Airspace is identified with a blue dashed line," and the chart prints its ceiling inside a dashed blue box with the last two zeros omitted 5. A "[25]" in a dashed blue box is a ceiling of 2,500 feet MSL.

Class D and the tower's hours

Class D exists while the tower operates. The AIM: "Class D surface areas may be designated as full-time (24 hour tower operations) or part-time. Part-time Class D effective times are published in the Chart Supplement." When the tower closes, the airspace changes: "Where a Class D surface area is part-time, the airspace may revert to either a Class E surface area or Class G airspace. When a part-time Class D surface area changes to Class G, the surface area becomes Class G airspace up to, but not including, the overlying controlled airspace." The Chart Supplement states which class applies: "The airport listing in the Chart Supplement will state the part-time surface area status (for example, 'other times CLASS E' or 'other times CLASS G')" 10. The dashed blue line on the chart does not change. The airspace inside the line changes.

Salinas

Salinas Municipal Airport is Class D while its tower operates. The FAA's airspace order designates it: "Airspace extending upward from the surface to, but not including 2,500 feet mean sea level within a 4.3-mile radius of the Salinas Municipal Airport. This Class D airspace area is effective during the specific dates and times established in advance by a Notice to Airmen" 11. The same order gives Salinas a Class E area "extending upward from 700 feet above the surface within a 13.1-mile radius," and an extension to the southeast. The extension brings Class E to the surface along the approach path while the Class D is in effect 11.

When the tower is closed

The order has no Class E surface area for Salinas. When the tower is closed, the surface inside the dashed blue line is Class G. Class E begins at 700 feet AGL, where the magenta vignette on the chart shows it. The pilot reads the status from three sources:

• the order, which lists no surface area
• the Chart Supplement entry, whose "other times" line states the class when the tower is closed
• the chart, whose magenta vignette shows the 700-foot floor.

The Warrior on the ramp before the tower opens sits in Class G. The Warrior in the pattern at 1,000 feet AGL is in Class E. The same pattern after the tower opens is in Class D, and the pilot talks to the tower.

Class E is the controlled airspace that is not A, B, C, or D. The handbook: "Class E airspace is the controlled airspace not classified as Class A, B, C, or D airspace. A large amount of the airspace over the United States is designated as Class E airspace." Its floor varies: "In most areas, the Class E airspace base is 1,200 feet AGL. In many other areas, the Class E airspace base is either the surface or 700 feet AGL" 12. The chart shows the floors as bands of shading. The Chart Users' Guide: "Class E Airspace exists at 1200' AGL unless designated otherwise," and "controlled airspace floors of 700' above the ground are defined by a magenta vignette; floors other than 700' that laterally abut uncontrolled airspace (Class G) are defined by a blue vignette" 13. Inside the faded magenta band, Class E starts at 700 feet AGL, and outside the band at 1,200 feet AGL.

Class E to the surface

A dashed magenta line marks Class E that extends to the surface. The Chart Users' Guide: "Class E Surface (SFC) Airspace is symbolized with a magenta dashed line" 13. The AIM gives the purpose: a "surface area designated for an airport where a control tower is not in operation," which "will be configured to contain all instrument procedures" 14. The Class E surface area contains the instrument approach at an airport with no tower operating. A dashed blue line means an operating tower. A dashed magenta line means an instrument approach with no tower operating.

Class G

Class G is the uncontrolled airspace. The AIM: "Class G airspace (uncontrolled) is that portion of airspace that has not been designated as Class A, Class B, Class C, Class D, or Class E airspace" 15. The handbook: "Class G airspace extends from the surface to the base of the overlying Class E airspace. Although ATC has no authority or responsibility to control air traffic, pilots should remember there are visual flight rules (VFR) minimums that apply to Class G airspace" 4. ATC issues no clearances in Class G. Under a magenta vignette, Class G is the lowest 700 feet, and where there is no vignette, the lowest 1,200 feet. The Chart Users' Guide gives the upper limit: "Class G Airspace within the United States extends up to 14,500' Mean Sea Level" 13.

The flight of N71MC

On August 8, 2009, at 11:53 in the morning, a Piper PA-32R Lance and a Eurocopter AS350 tour helicopter collided over the Hudson River. The collision was near Hoboken, New Jersey, at 1,100 feet. The airplane's pilot, a 60-year-old private pilot with 1,121 hours, and his two passengers died. The helicopter's pilot and five passengers died. The weather was clear 16.

The Hudson River lies under the New York Class B airspace, which the FAA designated around Newark, LaGuardia, and Kennedy. Under the Class B, the FAA left a corridor. The NTSB: "The Hudson River Class B exclusion area, which comprises Class E and Class G airspace, provides passage below the Class B airspace." At the time, the exclusion area "extended from the surface of the Hudson River up to, and including, 1,100 feet." The area "was Class E airspace from 700 to 1,100 feet and Class G airspace from the surface to 700 feet" 16. Aircraft in the corridor needed no clearance from anyone.

Pilots in the corridor talked to each other on a CTAF, 123.05. The helicopters flew the corridor all day. The airplane's pilot told Teterboro tower he would go "down the river" to Ocean City and climb to 3,500 feet. That climb needed a clearance into the Class B from Newark after Teterboro handed him off.

Teterboro cleared the pilot for takeoff at 11:48 with a left turn and 1,100 feet or below, the top of the corridor. The Teterboro controller then made a personal phone call. During the call, at 11:52:19, he told the pilot to contact Newark tower on 127.85. The NTSB: "The pilot responded to the TEB controller's instruction at 1152:20 and stated, 'one two seven point eight.' (This transmission was the last communication between the pilot and ATC)" 16. The controller did not correct the wrong readback. The Newark controller planned to turn the airplane to 220 degrees, away from the river traffic, and never heard from the pilot.

The helicopter lifted off from the West 30th Street heliport at 11:52 for a twelve-minute tour. It climbed to 1,000 feet across the river and then to 1,100 feet southbound along the west bank. Its pilot made a position report on the CTAF over the Stevens Institute in Hoboken. A second helicopter pilot on the ground saw the airplane approach from behind and to the right. He transmitted a warning on the CTAF as soon as the position report ended. The airplane's pilot was not on that frequency.

Radar generated a conflict alert to two controllers eleven times in the last minute. Neither controller recalled seeing it. At 11:53:14 the airplane, at about 150 knots, overtook the helicopter, at about 93 knots, and hit it from behind at 1,100 feet 16.

The NTSB's probable cause named "the inherent limitations of the see-and-avoid concept" and the Teterboro controller's "nonpertinent telephone conversation, which distracted him from his air traffic control (ATC) duties, including correcting the airplane pilot's read back of the Newark Liberty International Airport (EWR) tower frequency." The NTSB found three contributing factors:

• both pilots' ineffective use of the traffic information in their cockpits
• "inadequate Federal Aviation Administration (FAA) procedures for transfer of communications among ATC facilities near the Hudson River Class B exclusion area,"
• rules that "did not provide adequate vertical separation for aircraft operating in the Hudson River Class B exclusion area" 16.

The decisions that could have prevented the accident

Both aircraft were where the airspace allowed them to be. The corridor was Class E and Class G under a Class B ceiling, with a frequency of its own. Three decisions are listed below, each with the PAVE category that applied to it and the airspace fact that would have changed it.

Special use airspace appears on the chart by name and letter. The AIM: "Special use airspace (SUA) consists of that airspace wherein activities must be confined because of their nature, or wherein limitations are imposed upon aircraft operations that are not a part of those activities, or both." Prohibited and restricted areas are regulatory, and "warning areas, MOAs, alert areas, CFAs, and national security areas (NSA) are nonregulatory special use airspace." The chart shows each area "with the hours of operation, altitudes, and the controlling agency" 17. The names are:

• Prohibited, P and a number: "airspace of defined dimensions ... within which the flight of aircraft is prohibited" 18
• Restricted, R and a number: "unusual, often invisible, hazards to aircraft (e.g., artillery firing, aerial gunnery, or guided missiles)"
• Warning, W and a number: like restricted areas, but "the United States government does not have sole jurisdiction over the airspace," so they are offshore
• Military operations areas, named, not numbered: airspace "for the purpose of separating certain military training activities from IFR traffic"
• Alert areas, A and a number: "a high volume of pilot training or an unusual type of aerial activity" 19.

On the chart, "Prohibited, Restricted and Warning Areas are presented in blue and listed numerically," and each area "is identified by type and identifying name/number" beside it 20. The rules for each, and what a Warrior does at the edge of one, come later in the program. A letter and a number on the chart mean a rule applies inside the area.

The legend

The sectional chart's legend explains each symbol on the chart, and the Chart Users' Guide explains the legend. The guide's own example is a word a pilot cannot guess: "The type 'OBJECTIONABLE' associated with an airport symbol indicates that an objectionable airspace determination has been made for the airport" 21. The pilot looks up each unknown line, box, color, or word in the legend on the chart's margin or in the guide. The pilot never guesses. Six chart symbols mark different airspace boundaries:

• a solid blue line
• a solid magenta line
• a dashed blue line
• a dashed magenta line
• a magenta vignette
• a blue vignette.

A pilot who cannot tell these symbols apart opens the legend before the flight.