On 25 August 2002, a Douglas DC9-51 being operated by North West Airlines on a scheduled passenger flight from Toronto to Minneapolis had just taken off in day Visual Meteorological Conditions (VMC) when a Cessna 206 being operated on a passenger charter flight from Georgian Bay to Toronto unexpectedly carried out a missed approach from another runway. And despite last minute visual avoiding action came within close airborne proximity whilst still within the airport perimeter. There were no injuries to any of the 109 occupants of the DC9 or the 4 occupants of the Cessna.
An Investigation was carried out by the Canadian TSB. It was established that the amphibious, float-equipped, Cessna 206 had been given a Land and Hold Short Operations clearance for Runway 05 and on that basis, and contrary to prevailing ATC procedures for use of intersecting runways, the DC9 had been issued with a take off clearance from Runway 33L After the Cessna had touched down on Runway 05, the controller issued taxi instructions to the pilot, with instructions to hold short of Runway 33L but the pilot had then advised that he was going around because of a “landing gear problem”. The controller immediately instructed the Cessna pilot to commence a hard left turn. At the same time the DC9 flight crew had, just after becoming airborne, observed the Cessna and initiated a right turn. The actual distance between the aircraft after this avoiding action was assessed to have been approximately 30 metres laterally and 100 feet vertically at the Closest Point of Approach (CPA) which occurred over the threshold of Runway 15R, with the DC9 above the Cessna.
It was found during the investigation that the Cessna pilot had observed that the right main landing gear green light had not illuminated when the gear had been selected down during the approach, but that he did not advise ATC, who therefore had no idea of the increased possibility of a go around.
ATC procedures for the 33L / 05 Runway Pairing only permit ‘sequential operations’ rather than ‘simultaneous operations’. The differences between the two types of procedure depend on when an arriving aircraft crosses the landing threshold and when a departing aircraft crosses the intersection of the two runways. In either sequential or simultaneous operations, both aircraft may be in receipt of a landing or a take-off clearance, but for sequential operations, the controller must ensure that the landing aircraft does not cross the threshold of the landing runway until the departing aircraft has crossed the intersection of the two runways, or that the departing aircraft does not commence the take-off roll until the landing aircraft has safely landed and has slowed to taxi speed or has stopped prior to the intersection.
It was also noted that the risk of the Cessna 206 encountering the wake vortex of either the previous departed aircraft from Runway 33L, a Boeing 737, or the DC9 involved in the incident had not been considered by the controller.
It was considered that the use of the unauthorised procedure by the single controller involved had been an effort to maintain a high traffic flow rate in response to the long line of aircraft awaiting departure.
The runway layout and site of the conflict is shown in the diagram below taken from the Official Report. C-GGSG is the Cessna and N773NC is the DC9.
CYYZ Site map and conflict depiction, Source: TSB Aviation Investigation Report A02O0272
The Investigation concluded that:
“Because of the backlog of departing traffic and in an effort to expedite departures, the controller chose to use land and hold short operations (LAHSO) instead of sequential runway operations, which ultimately resulted in a near collision.
Various Safety Actions were taken as a result of the Incident and noted by the Investigation but no Safety Recommendations were issued as a result of it.
The Final Report of the Investigation was authorised for release on 26 November 2003 and may be seen in full at SKYbrary bookshelf: TSB Aviation Investigation Report A02O0272