On May 1, 1999, an Airbus Industrie A320 G-FNNA operated by Between Air Canada was involved in an aviation accident near and Canadian Airlines International, CA. Investigators recorded the probable cause as: The departure controller cleared the departing aircraft to an altitude above 9,000 feet prior to establishing that there would be adequate separation from arriving aircraft, and the arrival controller did not take positive action early enough to prevent the… This summary draws on records from the Transportation Safety Board of Canada (TSB); 2 related events involving the same aircraft type or operator are linked below.
A loss of separation occurred between an Air Canada A320 and a Canadian Airlines 737 near Calgary. The TSB found that controller coordination failures and a premature altitude clearance contributed to the incident.
Incident Overview and Sequence of Events On 1 May 1999, a loss of separation occurred in the Calgary Terminal Control Unit (TCU) involving Air Canada Flight 270 (ACA270), an Airbus A320, and Canadian Airlines Flight 960 (CDN960), a Boeing 737. ACA270 was inbound from Edmonton, Alberta, for an approach to runway 28 at Calgary International Airport. CDN960 had departed runway 34 and was en route to Toronto, Ontario. At 0653:00 mountain daylight saving time (MDT), ACA270 contacted Calgary Arrival and was cleared to descend to and maintain 10,000 feet. Shortly after 0657:50 MDT, CDN960 contacted Calgary Departure, reporting it was off runway 34 and climbing through 5,000 feet for 7,000 feet. The departure controller cleared CDN960 to turn right to a heading of 090 degrees and climb to flight level 250. The arrival controller then informed the departure controller that ACA270 was still at 10,000 feet. Approximately 50 seconds later, the departure controller realized that radar separation criteria of 1,000 feet vertical or 3 nautical miles lateral might be compromised. He instructed CDN960 to turn right to a heading of 110 degrees. At 0659:00 MDT, the arrival controller cleared ACA270 to descend to 6,000 feet at the pilot's discretion. Nineteen seconds later, the arrival controller cancelled the standard terminal arrival route (STAR) and cleared ACA270 to a heading of 110 degrees, parallel to CDN960. At this point, the two aircraft were 2 nautical miles apart at the same altitude, less than the required radar separation. The aircraft flew parallel courses until vertical separation was established, after which they received appropriate clearances to continue their flights. At an altitude of about 9,700 feet above sea level, the aircraft passed within 2 nautical miles of each other. The required spacing was 3 nautical miles laterally or 1,000 feet vertically. ## Contributing Factors and Findings The Transportation Safety Board of Canada (TSB) determined that the departure controller cleared the departing aircraft to an altitude above 9,000 feet prior to establishing that there would be adequate separation from arriving aircraft. Additionally, the departure controller attached a special function indicator (SFI) code letter “N” to the ACA270 data block, which indicated to the arrival controller that he may descend ACA270 below the flight management system (FMS) arrival altitude of 10,000 feet prior to the STAR dump point. The arrival controller recognized early that the two aircraft might be placed in proximity to each other and communicated to the departure controller that ACA270 was still at 10,000 feet. However, when the departure controller did not respond with a verbal acknowledgement, change the altitude clearance limit for CDN960, or cancel the code for ACA270, the arrival controller did not take any further action to ensure that the departure controller was aware of his concerns. Nor did he take positive action at that time to ensure separation between the aircraft he was controlling and CDN960. The departure controller had the option of using a “nine/ten split” procedure for aircraft separation but chose to employ a “look and go” option that required close monitoring of the inbound and outbound traffic. The nine/ten split is a procedure established and in use for about 17 years in the Calgary TCU, providing positive vertical separation when aircraft are in proximity to the airport. When used, this procedure reduces the controller's workload because the need for close monitoring of the traffic is less than that required by the “look and go” method. ## Management and Supervision Issues On 30 April 1999, at about 1800, the departure controller was involved in an operating irregularity in which there was a loss of separation. The on-duty shift manager assessed the controller as being capable of returning to work on his next scheduled shift. However, there was no assessment of the controller the following morning by the on-duty shift manager or the team supervisor. The Calgary TCU specialty team supervisor was not aware that the departure controller had been involved in an operating irregularity during the previous day. The on-duty shift manager did not meet with the departure controller prior to his resumption of duties on 1 May 1999. In the 30 days prior to the occurrence, the departure controller had worked an irregular shift schedule that had been changed several times at his or management's request. Of the 30 shift possibilities, only five (17 per cent) were unchanged. Scheduled days off were largely exchanged for overtime and, of the eight days off, five were due to the controller taking vacation. Shift work has the potential to impair an individual's ability to function at peak efficiency, although the beneficial effects of controlled shift work in maintaining an individual's efficiency have been well documented by the scientific community. ## Corrective Actions and Recommendations Following the occurrence, the management of the Edmonton Area Control Centre (ACC) instituted a temporary procedure whereby shift managers provide written documentation to their relief in the form of electronic mail on issues that have arisen during their shift. These electronic messages are accessed by the oncoming shift manager at the beginning of each shift and continue to be supplemented by verbal shift-change briefings. The Manager, Area Control Centre Operations is developing a formal shift-manager information database that will replace the electronic mail system. A procedure has also been instituted at the Edmonton ACC for handling operating irregularities. The shift manager responsible for removing a controller from duty is now responsible for ensuring that all the appropriate steps are taken to reinstate a controller to duty. This includes the requirement for the controller involved in an operating irregularity to be interviewed by the duty shift manager immediately prior to being returned for duty. The ACC has also instituted a policy whereby all controllers involved in an operating irregularity are required to undergo a proficiency check before being reinstated to duty. NAV CANADA's National Mandatory Air Traffic Control Refresher Training Plan for 1999/2000 and 2000/2001 notes that the Technical Training Division of NAV CANADA is committed to the development and complete delivery by 31 August 2001 of two 1-day human factors training modules on communications and on teamwork. The aim of the communications module is to make participants aware of the danger of poor or confusing communication in the operational environment. The aim of the teamwork module is to make participants aware of how an individual's skill and performance affect collaborative work and decision making. Transport Canada is chairing a tripartite working group on controller fatigue, including representatives from NAV CANADA, the Canadian Air Traffic Control Association, and Transport Canada. The related steering committee is chaired by the Assistant Deputy Minister, Safety and Security. This report concludes the Transportation Safety Board's investigation into this occurrence. Consequently, the Board authorized the release of this report on 1 August 2000.
Probable cause
The departure controller cleared the departing aircraft to an altitude above 9,000 feet prior to establishing that there would be adequate separation from arriving aircraft, and the arrival controller did not take positive action early enough to prevent the loss of separation.