Air transportation safety investigation Report A17O0038
Runway incursions between the parallel runways on the south complex of Toronto/Lester B. Pearson International Airport
The Transportation Safety Board of Canada (TSB) has identified the risk of collisions on runways as a serious risk in the Canadian aviation sector; this issue has persisted on the TSB’s Watchlist since 2010. Despite the efforts of government and the air industry, the risk of collisions on runways that results specifically from runway incursions remains a significant concern.
As a result of a number of runway incursions at Toronto/Lester B. Pearson International Airport (CYYZ), the TSB launched a safety issue investigation to examine the circumstances in more detail. This report contains the results of the investigation into 27 similar runway incursions that occurred on the south runway complex at CYYZ between June 2012 and November 2017. These were not the only incursions during this time at CYYZ; however, they posed substantial risk and shared many characteristics. All of the incursions involved aircraft that had landed on the outer runway and, despite receiving instructions from air traffic control and intending to hold short of the inner runway, did not do so.
Findings as to causes and contributing factors
- The short distance between the runway holding positions on the rapid exit taxiways (RETS) connecting the parallel runways, together with aircraft taxiing speeds that are faster than typical, limited the time available for flight crews to identify the visual cues designating the respective holding positions while completing post-landing tasks.
- Neither the inset nor elevated stop-bar lights at each runway holding position were oriented toward aircraft approaching from the taxiway curve. As a result, the majority of the lighting was not visible until aircraft were nearly at the stop line, which limited the time available for taxiing flight crews to recognize the visual cue.
- The intensity of the inset stop-bar lighting was insufficient to attract the crews' attention as they approached the runway holding positions, which contributed to the crews' not recognizing the positions.
- On the RETs, the runway holding positions are situated immediately following a 65° curve, and the distance of each runway holding position from the runway it protects exceeds that required by current guidance or commonly seen at other high-volume airports. Flight crews of arriving aircraft may be unfamiliar with the taxiway configuration and the distance to the runway holding position, and the respective crews of the aircraft involved in the incursions expected to see the runway holding position at a different location.
- The RETs provide direct access to the adjacent runways rather than to another transitional surface. Flight crews of arriving aircraft missed the visual cues depicting the runway holding position while conducting post-landing tasks, and, as a result, incurred on the inner runway, posing a serious risk of collision with departing aircraft.
- The holding positions on the D6 RET are the farthest from the runways that they protect, and the distance between its exiting and entering holding positions is the shortest, contributing to the higher rate of incursion at this intersection.
- All of the incursions examined involved flight crews who had been instructed to hold short, had accurately read back the instruction, had understood that they needed to stop, and had understood that they were approaching an active runway. However, despite those factors, they did not recognize the visual cues that identified the runway holding position, and the aircraft incurred on the runway.
- The airport charts, supplied to assist flight crews in planning their arrivals to CYYZ, identified the presence of runway incursion hot spots and contained general warnings about this type of incursion. However, the charts lacked sufficient information to impart a clear understanding of the risk or lead the crews to take effective mitigating measures.
- Although the operators' standard operating procedures (SOPs) included approach-briefing guidance encouraging flight crews to identify various hazardous situations, the SOPs did not require crews to discuss how those situations would be addressed. As a result, although some of the crews were aware of hazard hot spots at CYYZ and conducted briefings on them, the crews made no adjustment to their normal routines.
- Given that the approach briefings that were conducted did not describe an adjustment to the normal routine following landing, the flight crews in most cases maintained their standard practice of initiating the post-landing flows and checklists after exiting the landing runway. Those actions diverted the attention of one, and occasionally both, of the crew members from the more critical task of locating the runway holding position.
- SOPs that called for post-landing checks to be conducted after exiting the landing runway and those that required both flight crew members to be head-up when approaching runway hot spots did not take into account that the taxiways exiting the runway had direct access to the adjacent runway. As a result, it was left to the flight crews' discretion whether to follow one SOP or the other, and those whose aircraft incurred had chosen to complete the post-landing checks.
- The uncommon location of the runway holding positions, after the curve in their respective taxiways and farther back from the runway than normal, created a situation in which flight crews did not anticipate the need to stop in that particular location. As a result, the attention of the crews was not focused outside the aircraft at the appropriate time to identify the holding position.
- Those flight crew members whose attention was centred outside the aircraft while approaching the runway holding position were likely focused on a position farther down the taxiway, where the runway holding position is typically located. As a result, they likely disregarded the nearby visual cues, which did not conform to their mental model.
- Flight crews based in the United States were overrepresented in the number of incursions versus their Canadian counterparts, likely due to the fact that they are generally less familiar with the uncommon location of runway holding positions in RETs of the south complex at CYYZ.
- Regional jets were overrepresented in the number of incursions, likely due to the higher speed at which these aircraft types approached the runway holding position, both during the incursions and when compared with larger aircraft in general. This higher speed reduced the time available to identify the necessary visual cues.
Findings as to risk
- If runway holding positions are not established at distances that are consistent with those at other airports, there is an increased risk that flight crews will not recognize the visual cues designating those positions because of an expectation that the positions will be in the locations that they are accustomed to.
- If visual cues intended to alert flight crews to holding positions in uncommon locations are not sufficiently compelling to alter a flight crew's mental model of the situation, there is a continued risk that those cues will go unnoticed by crews.
- If inset stop-bar lights that are installed to draw attention to the runway holding position have differing brightness and beam spread or are obscured or non-functional, there is a risk that they will be ineffective in alerting flight crews to stop.
- If taxiways are not designed to limit the speed at which aircraft approach a runway holding position, there is a risk that aircraft will approach too quickly, reducing the time available for crews to identify important visual cues and for air traffic control to intervene before an aircraft incurs on the runway surface.
- If commonly used runway crossings are situated where aircraft departing from the runway are normally still on the ground or airborne at a low altitude, and an aircraft incurs on the departure runway, there is a significantly increased risk of collision.
- The recurrence of incursions following improvements made in 2013 and 2017 to the conspicuity of visual cues to runway holding position locations suggests that, if the runway holding positions remain in the same locations and flight crews are not primed to focus their attention outside the aircraft immediately upon exiting a landing runway, there is a continued risk that crews will miss the visual cues, regardless of further conspicuity improvements.
- If the RETs continue to provide direct access to adjacent runways and runway holding positions are moved closer to their respective departure runways, there may be a reduction in the frequency of incursions; however, there could be an increase in severity if an aircraft does incur on the runway surface while an aircraft is departing.
- If flight crews of aircraft that exit the landing runway on a RET are not provided with sufficient taxiway distance to accomplish post-landing tasks before reaching the runway holding position, and if their speed is not reduced by taxiway design characteristics when approaching these positions, there is a continuing risk that flight crews who perform these tasks and do not reduce their speed will incur on the inner runway.
Air traffic control
- If air traffic control transmissions that require immediate action by a flight crew are not sufficiently compelling to attract the crew's attention during periods of high workload, there is a risk that those instructions will not be recognized or acted on.
- If runway incursion monitoring and conflict alert system (RIMCAS) false alarms occur with routine frequency, there is a risk that RIMCAS alarms will be disregarded or that remedial actions will not be executed in a timely fashion.
- If audible alarms that are intended to alert controllers to various differing critical situations sound identical, there is a risk that those alarms will not draw the attention of controllers to the specific threats that they indicate.
- If user-selectable settings for stop-bar overrun alerting systems are not defaulted to ON, there is a risk that the alerts will be disabled at the time of an incursion and will not alert the controllers to the critical situation.
- If procedures do not require user-selectable settings for stop-bar light illumination to be selected to full intensity by default, there is a risk that the lights will be set to an intensity that is insufficient to draw the attention of flight crews.
- If inter-organizational procedures are not clear and specific with regard to immediate notification in the event of a serious incident, there is a continuing risk that the TSB will not be advised of the incident in sufficient time to secure on-board recordings, resulting in loss of information that may have been valuable to the assessment of safety deficiencies.
- If the portion of the automatic terminal information service (ATIS) message that is intended to alert flight crews to the risk of runway incursions on the inner runway does not clearly identify the hazard, there is a risk that crews will remain unaware of the hazard and that the use of this defence will not be effective.
- If approach briefings that draw attention to previously identified hazards do not also provide options to mitigate them, there is a continuing risk that flight crews will be unprepared to mitigate those hazards when they arise.
- If taxi briefings are not thorough, there is a risk that flight crews will be unaware of known or predictable hazards likely to be encountered during the taxiing phase, and this lack of awareness, and associated lack of planned mitigation, may result in a runway incursion or collision.
- If SOPs prompt flight crews to conduct post-landing tasks before coming to a stop, or before they are clear of all runways, there is a risk that those tasks will distract crews from more safety-critical responsibilities.