Mode Aviation
Reference No. AR201700116
Date reported 27 November 2017
Concern title Issues with the Sydney Tower advanced-surface movement guidance and control system (A-SMGCS)
Concern summary

The concern related to issues with the Sydney Tower advanced-surface movement guidance and control system (A-SMGCS).

Industry / Operation affected Aviation: Airspace management
Concern subject type Aviation: Air Traffic Control

Reporter's concern

The reporter expressed a safety concern related to the number of unknown vehicle identities being generated on the Sydney Tower A-SMGCS.

The reporter advised that they regularly receive indications of authorised vehicles showing as unknown vehicles operating at Sydney Airport with no indication of the vehicle’s identity. This is caused by the system deleting the known vehicle from a list of approved vehicles and duping the vehicle.

This results in controllers losing situational awareness due to the large number of duplicate identities, which distracts them from their primary task of separating aircraft. The controller has no easy way of identifying if the vehicle has approval to be operating airside on taxiways and runways or is limited to perimeter roads or worst-case scenario, if the vehicle is a rogue vehicle and should be treated as a security threat.

Operator's response (Operator 1)

Airservices Australia (Airservices) appreciates the opportunity to respond to the reported safety concern related to the number of unknown vehicle duplicate 'IDs' being generated in the Sydney Tower A-SMGCS.


The issue of unknown vehicle IDs or duplicate IDs is a known issue with the Sydney A­SMGCS system due to it being on an older software version than other A-SMGCS systems.

Airservices notes that over a period of time the Sydney A-SMGCS system automatically resolves the issue of duplicated IDs, however this does not meet ATC operational expectations.

In consultation with Saab Sensis Corporation, Airservices has successfully upgraded the software for A-SMGCS at all other locations to address this issue. However, it was established that upgrading the software at Sydney would potentially increase susceptibility of the system to multipath related system failure.

The remote units (RU) used as input sensors to the A-SMGCS at Sydney, have previously been impacted by multipath interference and on occasions leading to system failure. A number of attempts have been made in the past to address this problem, including a detailed study which did not identify a specific cause for the failure but attributed it to multiple factors in the environment within which the system operates.

As a result, the software for the A-SMGCS at Sydney was not upgraded.

Way Forward:

As an immediate mitigation strategy, local technicians have been advised to undertake simultaneous reboot of the processors which eliminates the issue of duplicate IDs. Airservices continues to work closely with Saab Sensis Corporation towards early resolution of the following:

  • Resolving the RU multipath interference issue, including looking at re-optimising Sydney A-SMGCS by considering relocating the affected RUs or transmitters
  • On successful mitigation of multipath interference, undertake the necessary software upgrade to align with software version at other A-SMCGS locations which will eliminate this issue.

Airservices is tracking both actions through the Airways Systems Issue Database (ASID).

As an ongoing mitigator, movement monitor staff now check and update the A-SMGCS system local list containing vehicle transponder IDs on a monthly basis. It should be noted that ATC have the option to manually 'tag' an unknown vehicle target at their console.

We continue to work with ATC to raise awareness of the issue and ensure that appropriate reporting is undertaken whenever duplicate IDs are observed.

Regulator's response (Regulator 1)

CASA has reviewed the REPCON and advises that the safety impact of the issue raised by the reporter will be investigated by CASA in early 2018.

Last update 12 July 2018