Near Misses Prompt Call For Ground-Based Conflict Alert System

Air Safety Week, Oct 9, 2000

Canadian regulators are poised to mandate a high-technology ground-based solution identified a decade ago to keep safe separation of aircraft after two recent mid-air collisions have stressed the need for more layers of collision avoidance defense.

Because of a near-miss between two Boeing 767s in January 1999 west of Winnipeg, Manitoba, the Transportation Safety Board of Canada (TSB) recommended that NAV CANADA consider the installation and operation of an automated conflict prediction and alerting system at Canadian facilities to reduce the risk of a mid-air collision.

The case involving Air Canada Flight 118 and Canadian Airlines Flight 987 pinpoints the need for a three-level collision avoidance foundation: technology in the air, technology on the ground, and alert air traffic controllers positioning aircraft.

The TSB investigation found that the air traffic controller experienced fatigue due to a significant amount of overtime and minimal time off between shifts. The controller did not perform a suitable scan of conflicting traffic prior to issuing climb clearance to ACA 118, which climbed through the flight level of CDN 987. The Traffic Collision and Alert System (TCAS) provided a warning to CDN 987 and then changed to a Resolution Advisory, indicating that the traffic was 800 feet below. The CDN 987 pilot climbed his aircraft at maximum performance to comply with company policy to adhere to RA directives.

The TSB stated that the last ground-based defense that could have prevented the occurrence was human redundancy. But that was absent because of limited personnel: only one operator was controlling the sector and the supervisor was actively controlling at another position.

The TSB is also investigating an April 11 incident involving two Lufthansa A340s that passed a mere 500 meters vertically. The planes, carrying approximately 300 passengers, were on the same altitude over the Gulf of St. Lawrence when the pilot of one aircraft received a TCAS advisory and alerted the controller.

At issue for Canadian officials is that TCAS technology, which warns of the danger of a mid-air collision and recommends evasive action, is not enough to prevent such incidents. Canadian regulation currently does not require TCAS installation in domestic, passenger-carrying airplanes, but this is not a large issue since so many planes flying in Canadian airspace also fly in the U.S., where TCAS is required on passenger aircraft. Neither the U.S. or Canada requires TCAS on cargo airplanes, but the Federal Aviation Administration is expected to be moving forward soon with a Notice of Proposed Rulemaking (NPRM) to implement such a law (see ASW, Sept. 18).

A ground-based collision avoidance system would undergo an operational evaluation by next March in Toronto, said a Canadian industry source. The project has been put back on track after NAV CANADA took authority of air traffic control after the now-defunct Canadian Aviation Safety Board recommended implementation of such a tool in 1990.

A different ground-based conflict alert radar system is in the software and design stage, said Bob Fullarton, manager of airspace and procedures at NAV CANADA. The system would adhere to parameters input by the air traffic controller for safe separation of aircraft. The system would send an alert to the air traffic controller if two aircraft would enter the parameter at the same time.

Controllers prefer to be the first line of defense. NAV CANADA wants to get to 105 percent of staffing requirements at its operation centers within the next two years to take into account for vacations, sick leave and special project work that leaves control centers stretched thin. >> Fullarton, 613/563- 5659