Mode Aviation
Reference No. AR2020-00051
Date reported 13 August 2020
Concern title Mandatory use of ADS-B in the Sydney basin.
Concern summary

Safety concerning regarding the mandatory use of ADS-B in the Sydney Basin. 

Industry / Operation affected Aviation: Airspace management
Concern subject type Aviation: Airspace

Reporter's concern

The reporter states that there are three main risk controls the operator utilises to avoid aircraft proximity events. They are, in order of effectiveness:

  • Traffic Collision Avoidance System (TCAS), which allows our helicopters to see other aircraft that are fitted with transponders. This provides early warning of proximity traffic so that avoidance action can be taken.
  • Air Traffic Control advice of conflicting traffic, which requires aircraft to either be fitted with a transponder or to be within range of primary radar returns. Primary radar is not effective in western Sydney at low levels. Furthermore, ATC are not responsible for separating VFR traffic, and thus it is extremely rare to receive traffic advice in the Sydney basin due to the airspace congestion and high workloads of ATC personnel.
  • See and avoid. This requires the aircrew to visually identify traffic and take avoidance action.

The reporter states that in a recent proximity event, the conflicting aircraft did not have a transponder, and the controller did not pass traffic on the primary return, and thus the two most effective controls were rendered ineffective. Despite the Sydney basin being the busiest airspace in the country, this aircraft was not breaking any rules. Transponder carriage and use is only required for VFR aircraft in Class A, C, E and G airspace above 10,000 ft, or for aircraft manufactured after 2014.

Bankstown Airport (Class D) and its surrounding Class G airspace do not require the carriage of a transponder for VFR aircraft. The fact that CASA have mandated transponder fitment for aircraft manufactured after 2014 indicates the importance CASA places on the use of transponders as a risk control to avoid aircraft proximity events.

The reporter advises that there have been numerous studies into the limitations of see and avoid. Including a see and avoid ATSB report. This report concluded that 'the see-and-avoid principle in the absence of traffic alerts is subject to serious limitations'. Unalerted see and avoid has a 'limited place as a last resort means of traffic separation at low closing speeds' and is 'completely unsuitable as a primary traffic separation method for scheduled services'.

The reporter believes that with this in mind, there is only one control available to avoid proximity events out of Bankstown Airport, and that is to depart under the IFR or to remain within controlled airspace at all times. This is not a viable control for helicopter rescue operations in the Sydney basin.

The reporter believes that operations within the Sydney basin should require the carriage and use of a transponder for all aircraft. This would require either a change in the regulations on carriage of transponders for VFR aircraft, or the designation of a new class of transponder mandatory airspace surrounding Sydney..

Regulator's response (Regulator 1)

CASA is satisfied that the risk of a mid-air collision is mitigated to achieve an acceptable level of safety based on current regulations related to airspace procedures, rules of the air, ATC services, technology, communication, training and airmanship.

The use of ADS-B is not an alternative to regulation and by itself it may not prevent a mid-air collision.

The benefit of ADS-B can only be realised if both aircraft are fitted with ADS-B in and out. However, ADS-B is not compatible with TCAS so many RPT/IFR aircraft cannot be detected by or be able to detect ADS-B fitted aircraft.

Last update 09 July 2021