Aviation occurrence briefs

Separation issue involving Aero Commander 500-U and Mooney Aircraft Corp M20J, 28 km SSW of Bourke, NSW, on 18 January 2018

Status: Completed
Investigation completed


Occurrence Briefs are concise reports that detail the facts surrounding a transport safety occurrence, as received in the initial notification and any follow-up enquiries. They provide an opportunity to share safety messages in the absence of an investigation.

What happened

On 18 January 2018, an Aero Commander 500-U departed Cobar, New South Wales (NSW), for Charleville, Queensland (Qld). Another aircraft, Mooney M20J, was also airborne at the same time, flying from Broken Hill, NSW, to Archerfield, Qld.

During cruise at 8,500 ft, the pilot of the 500-U observed traffic on their electronic flight bag (EFB) application in their 10 o’clock position at 10 NM. The EFB application indicated the traffic was within 200 ft of the 500-U’s altitude. The pilot of the 500-U reported that the application displayed the relative positions of the two aircraft remained constant and the distance between them was reducing.

The pilot of the 500-U initiated contact with the crew of the M20J, resulting in the M20J descending to 7,500 ft. Two minutes later, the 500-U pilot observed the M20J passing directly underneath, crossing their track at almost 90 degrees.


The aircraft passed each other in Class G airspace. Class G airspace is non-controlled airspace in which IFR[1] and VFR[2] aircraft are permitted to operate without a clearance. There is no air traffic control separation service in Class G airspace.


The pilot of the 500-U reported that a grey haze prevented sighting the M20J until it passed directly underneath.

Safety message

This occurrence highlights the importance of following the altitude requirements for VFR flight (see Figure 1) in uncontrolled airspace. This is especially significant when considering the limitations discussed in the ATSB research report Limitations of the See-and-Avoid Principle.

Figure 1: Table of VFR cruising levels
Table of VFR cruising levels.  Source: Aeronautical Information Publication Australia

Source: Aeronautical Information Publication Australia

It also highlights the importance of monitoring area frequency for potential traffic and that electronic aids can be used as a supplementary tool that may enhance maintaining situational awareness.

About this report

Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, no investigation has been conducted and the ATSB did not verify the accuracy of the information. A brief description has been written using information supplied in the notification and any follow-up information in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.



  1. Instrument flight rules (IFR): a set of regulations that permit the pilot to operate an aircraft in instrument meteorological conditions (IMC), which have much lower weather minimums than visual flight rules (VFR). Procedures and training are significantly more complex as a pilot must demonstrate competency in IMC conditions while controlling the aircraft solely by reference to instruments. IFR-capable aircraft have greater equipment and maintenance requirements.
  2. Visual flight rules (VFR): a set of regulations that permit a pilot to operate an aircraft only in weather conditions generally clear enough to allow the pilot to see where the aircraft is going.
General details
Date: 18 January 2018   Investigation status: Completed  
Time: 1130 EST    
Location   (show map): 28 km SSW Bourke    
State: New South Wales    
Release Date: 28 March 2018   Occurrence category: Incident  
Report status: Final   Highest injury level: None  

Aircraft 1 details

Aircraft 1 details
Aircraft manufacturer Aero Commander  
Aircraft model 500-U  
Type of operation Private  
Sector Piston  
Damage to aircraft Nil  

Aircraft 2 details

Aircraft 2 details
Aircraft manufacturer Mooney Aircraft Corp  
Aircraft model M20J  
Type of operation Private  
Sector Piston  
Damage to aircraft Nil  
Last update 09 September 2019