Aviation Safety Letter 4/2004

Managing Collision Risk in Class G Airspace in Canada

by Don Henderson, Manager, Level of Service and Aeronautical Studies, NAV CANADA

During the course of recent consultation and other meetings held between NAV CANADA and various air carriers and — particularly in the vicinity of high-density airports. These concerns focus around the following areas: pilot assumptions with respect to services provided by air traffic control (ATC); pilot vigilance; use of VFR routes, transit routes and associated reporting points; and, communication practices.

The systems approach

Managing the risk of collision between aircraft is one of the primary goals of the air traffic management system. This can only be accomplished within a "total system" framework where user-conduct rules are harmonized with service provision. Understanding the contribution that each element makes to overall system safety performance is essential in effectively reducing collision risk.

Risk and defensive barriers

There are three fundamental techniques that can be employed to manage the risk of collision. The first is to design airspace and conduct flight operations so as to preclude the opportunity for conflict or risk of collision. Examples of this are to specify flight along non-intersecting tracks or to define a volume of airspace for the exclusive use of one user.

A second technique is to alter flight trajectories to resolve conflicts and avoid collisions. Examples of this include the directions pilots receive from ATC when being "vectored".

Finally, the "rules of the air" are applicable to pilots, and compliance introduces a proven defence barrier against collision risk.

In practice, the risk of collision is not normally managed by the application of one technique or the other, but by practices and procedures that to some extent employ all three techniques. Thus, classes of airspace, the provision of ATC services, radar or some other means of surveillance or position reporting, communications and regulations (rules of the air) come together to create an operating system.

In addition, arrival and departure procedures, routes and airways are designed to further facilitate a safe and efficient operating environment. This system can have different configurations and components depending on traffic volume and complexity. For controlled airspace these defensive barriers can be expected to perform in a predictable way.

Class G airspace

For uncontrolled airspace (class G) it is different. While VFR routes, transit routes, reporting points and recommended practices can be put forward, they are not fully supported through regulations, and depend on pilots understanding the system and doing the right thing — the right thing is called airmanship.

If pilots use the system in the way it is intended to be used, they can reduce their risk and improve efficiency of their operations. If "ad hoc" procedures are applied, if pilots decide that "this is the way we have always done it" or "it's quicker this way and anyway I don't have to do it that way" then there may be unintended negative consequences.

Pilots are solely responsible for traffic separation in class G airspace. Avoiding conflicts requires pilots to communicate with each other on appropriate frequencies, advise of their intentions, and plan accordingly.

If there are specific recommended practices for an area, such as VFR routes, transit routes, reporting points or an aerodrome traffic frequency (ATF), pilots' voluntary compliance is required to ensure the system performs as intended, and that acceptable safety is achieved.

In some instances, ATC or flight service specialists may provide additional information, including traffic information, if their workload permits. This in no way implies that pilots are being provided separation, or their flight is being controlled in any way. The pilots are entirely responsible for flying the aircraft.

About VFR routes

VFR routes or transit routes are often published in order to reduce the risk of collision in heavily-traveled VFR corridors as well as to provide an aid to ATC for the purposes of expediting arrivals and departures from airports.

VFR routes are advisory; that is, they are not mandatory, but adherence to the routes reduces the risk of conflicts.

See and Avoid

Pilots are expected to follow the rules by flying the appropriate altitudes, communicating when required, and conforming to recommended practices to reduce the probability of conflict. The "see and avoid" concept still plays a key role and requires vigilance on the part of pilots — particularly in high-traffic areas.

In the future, technology will provide pilots with a traffic picture in the cockpit to assist with reducing collision risk. Even then, there will be no substitute for a good look out.

Airspace classification system

The airspace classification system defines the air traffic services (ATS) provided, and pilot responsibilities.

The classes applicable to the provision of ATC services are:

Class A:  Only IFR flights are permitted; all flights are provided with ATC services, and are separated from each other.

Class B:  IFR and VFR flights are permitted; all flights are provided with ATC services, and are separated from each other.

Class C:  IFR and VFR flights are permitted; all flights are provided with ATC services, and IFR flights are separated from other IFR flights, and provided with conflict resolution from VFR flights. VFR flights are provided with conflict resolution from IFR flights, and receive traffic information in respect of other VFR flights. Conflict resolution between VFR flights is available upon request, equipment and workload permitting.

Class D:  IFR and VFR flights are permitted; all flights are provided with ATC services, IFR flights are separated from other IFR flights, and receive traffic information in respect of VFR flights. VFR flights receive traffic information in respect of all other flights. Conflict resolution between VFR flights is available upon request, equipment and workload permitting.

Class E:  IFR and VFR flights are permitted; IFR flights are provided with ATC services, and are separated from other IFR flights. All flights receive traffic information as far as is practical.

Class F/G:  All other airspace is either class G uncontrolled airspace or class F special use airspace.

In conclusion, if you are a pilot flying in class G airspace, the responsibility for collision avoidance is all yours — you have control!

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