In coordination with the local Federal Aviation Administration (FAA) office we were tasked to work with a major airline to reduce the risk of runway incursions. Runway incursions involve the crossing of an active runway by an aircraft or vehicle that increases the risk of a collision with an approaching aircraft on final approach. The focus was upon three runway incursion events involving aircraft technicians conducting maintenance taxi operations.
Using the Trajectories® tool and techniques, a team of advisors worked with aircraft technicians to understand and build a predictive model describing the paths of risk that would lead to the undesired outcome of having an aircraft cross an active runway. Within this analysis we evaluated four areas that could impact the risk related to this event. These four areas include workload, time critical tasks, airport specific peculiarities, and the choices being made within this operational activity.
Within the Trajectories® analysis the modeling team developed a workload distribution for the left and right seat technician during different phases of taxiing and during non-normal taxi operations. The team then identified a basic set of failure modes (errors and behavioral choices) that would contribute to a runway incursion. The modeling team then pieced together the combinations of failures into a series of trajectories. Within the trajectories analysis the following failures presented significant paths of risk to the undesired outcome:
- Technicians are distracted or confused by radio traffic in the flight deck
- Technician’s misinterpret airport signage
- Right seat not engaged in verifying current location while left seat is conducting aircraft movement
- Right seat writes down different clearance than is given by air/ground traffic control
- Left seat does not hear clearance because right seat makes call before left seat has completed aircraft start
The recommendations resulting from the analysis included: a distribution of workload during critical taxi phases resulting in suggested specific duties for the left and right seat technicians, the maintenance of a sterile cockpit during taxi, and the knowledge and skill requirements to effectively taxi an aircraft. The goal of the analysis at a high level was to eliminate any single human errors, or any common (single failure path) human errors between the left and right seat technicians that would result in a runway incursion. The potential interventions are illustrated below:
- When taxiing, monitor only ground control plus possibly one dedicated maintenance frequency for taxi operations
- Require airport taxi familiarization training or qualification on airport runways
- Require right seat to follow movements on airport map. Require left seat to announce movements (e.g., turn left at taxiway bravo) and require right seat to readback and confirm (turn left at taxiway bravo, agreed)
- If clearance is written down, right seat must read clearance to left seat immediately upon completing of writing down clearance
- Right seat confirms readiness of left seat before making call to ground control
The trajectories analysis predicted if these interventions or versions of them were to be implemented within maintenance aircraft taxi operations, it could result in a 98% reduction in total events.