What happened
At approximately 19:35 MDT, a Canada 3000 Airbus 320, registered CMM368, departed Calgary International Airport from runway 28, climbing toward a planned flight level of 250. Simultaneously, a Turbo-Commander 690, registered N48BA, departed runway 34 for Kalispell, Montana, with instructions to climb to flight level 210.
During the initial climb, the controller vectored CMM368 onto a heading of 090°M. As the aircraft reached approximately 12,000 feet and accelerated to 300 KIAS, the crew received a Traffic Advisory (TA) from the Traffic Collision Avoidance System (TCAS), indicating another aircraft 700 feet below and climbing. This was immediately followed by a Resolution Advisory (RA) commanding a descent. The pilot of CMM3LE8 initiated the descent, while the pilot of N48BA sighted the larger aircraft and increased his rate of climb.
As a result, CMM368 came within 500 feet horizontally and 500 feet vertically of N48BA, violating the required separation of 3 nautical miles or 1,000 feet.
The investigation
The investigation examined the departure procedures and controller actions at Calgary International Airport. While the airport was using a co-active runway system, standard procedures dictate that north/eastbound traffic use runway 34 and south/westbound traffic use runway 28. To reduce taxi time, the controller permitted both aircraft to depart from non-standard runways.
Investigators found that while the Airbus 320 was climbing, the pilot increased the aircraft's speed to 320 KIAS. This change in speed caused the rate of climb to drop from approximately 3,200 fpm to 800 fpm. The controller, relying on previous experience with similar aircraft, expected a much higher climb rate and did not recheck the progress of the aircraft for approximately two minutes prior to the TCAS alert.
Findings
- The air traffic controller failed to follow established separation criteria for aircraft entering the same airspace.
- The controller's decision to allow departures from non-standard runways to reduce taxi time increased the risk of conflict.
- The controller did not adequately monitor the progress of the two aircraft for about two minutes before the TCAS alert.
- The controller's monitoring was hindered by expectations regarding the aircraft's performance and the distraction of other traffic responsibilities.
- The reduction in the Airbus 320's climb rate, caused by the pilot's selection of a higher cruise speed, was not detected by ATC.