Controller Detection of Manoeuvring Area Conflicts – Safety Barriers

Controller Detection of Manoeuvring Area Conflicts – Safety Barriers


This article describes the prevention and mitigation barriers used for detecting conflicts on the manoeuvring area. It also gives information on barrier effectiveness based on real events.

Prevention Barriers

The following barriers, when deployed and employed correctly, are capable of alerting ATC in time to prevent runway incursions and ground conflicts. With regard to events on the Manoeuvring Area, these barriers are capable of alerting ATC before standard levels of safety are compromised:

  • ATCO memory aids for issued (not issued) clearances. Used to enhance the controller’s situational awareness and remind of issued clearances. Examples of these are:
    • Buttons or switches used by the controller when a clearance affecting the manoeuvring area is issued.
    • Flight strip arrangement rules (e.g. if a take-off/landing clearance is issued to an aircraft, its flight strip is put into a red holder).
  • ATCO direct visual detection. One of the main responsibilities of a tower controller is to constantly observe the situation on the manoeuvring area and verify that all clearances are properly complied with.
  • ATCO visual detection using remote camera displays. These are used when parts of the manoeuvring area cannot be observed from the control tower (e.g. due to obstacles, aerodrome layout, etc.). They supplement the direct visual detection.
  • ATCO resolution following pilot/driver report. This barrier relies on voluntary information from another person. While usually this cannot be legally described and written down as a procedure, experience shows that this barrier turns out to be one of the most effective tools.
  • ATCO detection of occupied runway by use of basic Surface Movement Radar (SMR). This tool provides surveillance information in poor visibility conditions when direct visual detection and remote cameras are not effective. It also helps controllers to identify smaller objects (vehicles or aircraft) which are at relatively long distance from the control tower. The disadvantage is that normally there are no visual or audial warnings and therefore the controllers needs to divert their attention from visual observation in order to use the SMR.
  • Advanced Surface Movement & Guidance Control System (A-SMGCS) level 1. This tool is an enhanced version of the SMR. It provides identification of both aircraft and transponder-equipped vehicles. The tool relies on the proper use of transponders. If procedures are strictly followed, A-SMGCS provides reliable information on the traffic situation both on the manoeuvring area and the immediate aerodrome vicinity.
  • Advanced Surface Movement & Guidance Control System (A-SMGCS) level 2. This tool is an enhancement of the A-SMGCS Level 1. It provides conflict alerts in addition to aircraft/vehicle identification. The logic is similar to STCA used in area control. While this feature is a great enhancement compared to A-SMGCS Level 1 it only warns the controller of immediate risks and does not take into account the issued clearances (which might be conflicting).
  • Integrated Tower Working Position (ITWP). This is an ATC system that displays both traffic situation and controller input (ATC clearances) which enables the use of “early warning” features that:
    • highlight any non-conformance to clearance;
    • highlight the potential consequences of any incorrect clearance.
  • Use of discrete names for holding positions and pilot reports (e.g. reporting point REKRA instead of P2). This barrier helps reduce the chance of mishearing or misunderstanding a clearance.
  • A procedure stating that all vehicles entering a runway should display high visibility flashing/strobing lights on in all visibility conditions. Following such a procedure enhances the situational awareness of all participants (controllers, pilots, vehicle drivers and other people on the manoeuvring area) as it gives them information about the flight crew intentions. This also improves the effectiveness of the “ATCO resolution following pilot/driver report” barrier.

Mitigation Barriers

The following barriers, when deployed and employed correctly, are capable of alerting ATC to a runway incursion or a ground safety event in sufficient time for ATC to act in order to prevent a ground collision:

  • ATCO direct visual detection;
  • ATCO visual detection using remote camera displays;
  • ATCO detection following pilot/driver report;
  • ATCO detection using basic SMR;
  • ATCO detection it using A-SMGCS level 1;
  • ATCO detection it after alert from A-SMGCS level 2;
  • ATCO detection after alert from ITWP;
  • ATCO detection after alert from airport ground systems that detect entry onto the runway (e.g. magnetic loops or lasers).

Depending on the stage of the conflict, all these (except for the last one) can be either prevention or mitigation barriers. They give the controller a chance of a last-minute conflict resolution.

Barrier Effectiveness

dedicated study has concluded that:

  • ATCO detection after alert from the use of input and display of the ATC clearances and surveillance data (ITWP) is likely to be the most effective ATC tool in the prevention and mitigation of runway incursions and ground safety events. This functionality is not yet widely available; however, this study does lend strong support.
  • Proactive alerts from pilots and drivers that lead to ATC detection and resolution are likely to be very important barriers, especially in reducing the risk of collision in runway incursions.
  • ATC direct visual detection and the use of A-SMGCS level 2 are both strong barriers in the prevention and mitigation of runway events.
  • ATC detection of incorrect runway presence, using remote camera displays is a strong mitigation barrier as it does not necessarily depend on good visibility and line of sight.
  • ATC memory aids are likely to be strong barriers that aid ATC perception and memory. It is these areas of ATC action however that fail most often in actual events.
  • The barrier that halted actual safety events most often was acting upon alerts received from pilots and drivers. The study therefore supports initiatives such as Local Runway Safety Teams in promoting the “one team ethos”.

The barriers that were breached most often were:

  • ATCO Direct Visual Detection;
  • ATC Memory Aids;
  • belated (last-minute) ATCO Direct Visual Detection;
  • ATCO detection with A-SMGCS level 1.

The barriers that most often successfully stopped the event were:

  • ATCO resolution after pilot/driver alert;
  • belated (last-minute) ATCO Visual Detection;
  • belated (last-minute) pilot detection.

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