Mid-air collision avoidance between two business jets over Canadian airspace

Casualties unknown • CA

Two business jets flying on reciprocal tracks nearly collided over Canada after an altitude assignment error went undetected by air traffic controllers.

What happened

On a flight traveling from San Jose, California, to Bedford, Massachusetts, a Cessna Citation X, registration N217AL, was cleared to maintain flight level 430. This altitude is typically reserved for westbound traffic. Simultaneously, a Gulfstream V, registration N128GV, was flying westbound from Connecticut to San Francisco, also maintained at flight level 430. Both aircraft were operating on the J16 airway between the Peck and London VORs.

At 1342 Eastern Standard Time, the two aircraft encountered a potential collision risk. The flight crews responded to both traffic alerts and collision-avoidance system (TCAS) resolution advisories. The aircraft passed each other with a lateral separation of 1 nautical mile and a vertical separation of 900 feet. There were no injuries and no damage to either aircraft.

The investigation

The investigation examined the hand-off procedures between the Cleveland Air Route Traffic Control Centre (KZOB) and the Toronto Area Control Centre (CZYZ). It was established that the KZOB controller did not treat the altitude assignment as a significant issue during the hand-off, which meant the required approval request was not properly processed.

Furthermore, the investigation looked into the transition of personnel within the Oakville sector of the Toronto Area Control Centre. The data controller had recently taken over the position, and the radar controller had also been relieved. The investigation found that the flight-progress strip for N217AL was not properly marked or highlighted to indicate its inappropriate altitude. Additionally, the automated air traffic system's alert for aircraft at an inappropriate altitude had been disabled to prevent false warnings, removing a critical layer of automated detection.

Findings

  • The Cessna Citation X was permitted to fly at an altitude inappropriate for its direction of flight without being re-cleared.
  • Coordination protocols between the Cleveland and Toronto control centers regarding altitude approvals were not followed.
  • The failure to mark the flight-progress strip prevented controllers from identifying the altitude conflict.
  • The handover briefing between the outgoing and incoming radar controllers did not communicate the existence of the conflict.
  • The automated system alert for inappropriate altitude was disabled, preventing the radar controller from receiving an automated warning.

Probable cause

The near-collision was caused by a failure to follow established altitude approval protocols during air traffic hand-offs, compounded by inadequate marking of flight strips and the disabling of automated altitude conflict alerts.

Frequently asked questions

What happened in the 2012-03-08 London, Ontario, 20 nm NW accident near CA?

Two business jets flying on reciprocal tracks nearly collided over Canada after an altitude assignment error went undetected by air traffic controllers.

What aircraft was involved and where did it happen?

The accident on 2012-03-08 involved a London, Ontario, 20 nm NW, operated by NAV CANADA − Toronto Area Control Centre, at CA.

What was the probable cause of the accident?

The near-collision was caused by a failure to follow established altitude approval protocols during air traffic hand-offs, compounded by inadequate marking of flight strips and the disabling of automated altitude conflict alerts.

Loading the flight search…