Collision Avoidance

COLLISION AVOIDANCE AND AIRSPACE

This is how your last three seconds could look to an F-16 pilot.

Regulations say we should all "see and avoid" each other when we are flying in visual meteorological conditions. That isn't as easy as it sounds, as our previous illustration shows. Only 5% of mid-air collisions are head-on. Most involve one aircraft overtaking another. Since gliders are usually the slower aircraft, that suggests that our greatest threat is not where we are likely to be looking when flying straight. The situation is no better when we are circling in a thermal. Because our area of sharp vision is only about ten degrees wide, the recommended method of scanning for traffic is to divide the area into ten degree segments and examine each for about two seconds. That would require that we examine 36 ten degree segments at two seconds each for a total of 72 seconds. But it only takes about 16 seconds to complete a circle when thermalling at a 45 degree bank. That means we'd better be looking at the segment where the traffic is if we expect to see it.

We could just give up and rely on the "Big Sky - Little Airplane" theory of collision avoidance, but maybe there are some things we can do to improve our chances of success. One is to know where traffic is more likely to be and avoid those areas when it is reasonable to do so. If it is not, then at least exercise extra caution. Some of the places where airplanes are more likely to be include, airports and airways for civilian aircraft and special use airspace and Military Training Routes for military aircraft. In the following table we show examples of these along with some of the restrictions and precautions related to their use.

Class B airspace is the most restrictive for glider pilots, and is usually the most complex. In this partial view of PHX you can see the different shapes and altitudes of different segments. Entry requires a clearance (ergo two-way communication) and a Mode C transponder with altitude encoding. Gliders are exempt from the Mode C requirement within the 30 NM Mode C Veil, but not within Class B airspace nor above it to 10,000 feet MSL.

Perhaps the most serious collision risk for gliders operating near busy commercial airports involves airplanes descending to the airport on Arrival Routes. A collision involving a glider and an air carrier would likely be fatal to the sport of soaring as well as the people involved. Arrival Routes are not shown on any charts normally used by glider pilots except for the symbol shown here from an Area chart.

From the glider pilot's perspective, Class C is not significantly different from Class B. Two-way communication is required for entry, but not specifically a "clearance", and Mode C transponder with altitude encoding is required in and above Class C up to 10,000 feet MSL. This illustration shows two overlapping Class C areas.

Two-way communication is normally required for entry into Class D airspace. The Aeronautical Information Manual recommends the initial call be made 15 miles out. The tower frequency is shown on the chart after the letters "CT". Class D airspace usually extends from the surface to 2,500 feet AGL, but in this case overlying airspace restricts the top to 4,200 feet MSL, shown in the small box as "-42".

Communication is not required for operations in Class E airspace, but the Aeronautical Information Manual recommends "self-announcing" to other traffic 10 miles out and entering downwind, base and final when landing at a non-tower airport. The common traffic advisory frequency, CTAF, is indicated on the chart by the letter "C" enclosed in a solid colored circle.

Victor Airways, V-16 in this illustration, are shown in blue on aeronautical charts. They are based on VOR navigation facilities, and are used primarily by general aviation pilots. Military Training Routes (MTRs) are shown in gray, with the letters "VR" or "IR", indicating visual or instrument routes, followed by the route number. Glider pilots should be alert for high speed military aircraft along these routes. Planned activity can be obtained from Flight Service.

Military Operations Areas (MOAs) have a magenta crosshatched border. Information about their times of use and the applicable altitudes can be found on the border of the chart. No clearance is necessary for operation in MOAs, but glider pilots should exercise caution when the area is active.

Restricted Areas, shown on charts with a blue crosshatched border, require a clearance to enter during times of use. Times and altitudes are shown on the chart border, along with the controlling agency. It will usually be easier for glider pilots to obtain information about restricted areas by contacting Flight Service.

Alert Areas are also depicted with blue crosshatched borders. That is difficult to see in this illustration because most of the Alert Area's border coincides with the magenta boundary of Class E airspace beginning at 700 feet AGL. Alert Areas, like MOAs, require no clearance, but extra caution is advised.

Most of the practical test failures related to airspace are because of the inability to correctly identify airspace on a Sectional Chart and/or know the restrictions applicable to that airspace. U.S. airspace, other than special use airspace, is divided into six classes, A through G (there is no Class F in the U.S.). Class A, starting at 18,000 feet MSL, is available for glider flights only by prearrangement for a "wave window". Class B and C require altitude encoding transponders in and above up to 10,000 feet MSL, and two-way communication, and Class D usually requires only communication. Gliders can fly in most of Class E and Class G with no restrictions at all.

Since most glider operations in the U.S. are conducted in visual meteorological conditions, pilots need to be aware of the visibility and cloud clearance minimums for legal VFR flight. These minimums are established help give pilots the opportunity to "see" other aircraft in time to "avoid" them. When you consider that there are six airspace classes, three visibility minimums, and three cloud clearance minimums, keeping them all straight seems like a formidable task. It gets a little easier when you recognize that there are only five combinations of visibility and cloud clearance, and two of those have unique application. Five mile visibility and cloud clearance of 1,000 ft below, 1,000 ft above and 1 mile horizontally applies to everything above 10,000 ft MSL all the time. Three mile visibility and clear of clouds applies to Class B all the time. At night, everything else is three miles visibility and cloud clearance of 500 ft below, 1,000 ft above and 2,000 ft horizontally. In the day time, Class G visibility below 10,000 MSL drops to one mile, and below 1,200 ft AGL cloud clearance becomes clear of clouds.

FAR 61.89 further restricts Student Pilots to three mile visibility during the day and five miles at night. FAR 91.155 has a couple of exceptions for airplane and helicopter pilots but none for gliders.

There is a lot pilots should know about airspace and minimums and equipment requirements, but by far the most practical test failures related to collision avoidance are simply due to failure to make a clearing turn before demonstrating a stall. Many instructors teach students to make two 90 degree turns prior to any maneuver. The number of degrees turned is far less important than checking to see that the airspace you will be occupying during the maneuver will not also be occupied by someone else. Visibility from the front seat of a trainer such as the Schweizer SGS 2-33 is pretty good just about everywhere except behind and below, but you need to make a turn to check there.

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