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At 1142 Eastern Standard Time1 on 26 September 2011, a Beech Aircraft Corporation, A36 (Bonanza) aircraft, registered VH-YEN (YEN), was flying north at 2,700 ft from Camden, New South Wales, to Queensland. At the same time another Bonanza aircraft, registered VH-IOL (IOL) was conducting aerial survey operations above the Ravensworth coal mine, south-east of Scone, New South Wales. Both aircraft were operating under the Visual Flight Rules (VFR) in visual meteorological conditions (VMC). The aircraft were flying in class G airspace, clear of any significant aerodromes. The radio frequency for VFR operations in that area was Brisbane Centre air traffic services (ATS) on 124.8 MHz.

The pilot of IOL reported that he was concentrating on navigational guidance equipment to maintain an accurate flight path on a westerly heading when he heard a radio broadcast from ATS, stating that two aircraft were visible on radar in his vicinity, on converging trajectories. The pilot directed his vision to search for other aircraft and reported that he observed another aircraft to the front, passing from left to right on a northerly heading. The pilot turned his aircraft left and observed the other aircraft passing to his right with approximately 300 ft horizontal and 50 ft vertical separation.

The pilot read the call sign VH-YEN, visible on the aircraft fuselage as they passed each other. The pilot of IOL estimated that YEN would soon fly near Scone, and a few minutes later made contact with the pilot of YEN on the Scone Common Traffic Advisory Frequency (CTAF).

The pilot of YEN reported that he had not been monitoring the Brisbane Centre radio frequency because the aircraft was at or below the minimum altitude to assure radio communication with ATS. The pilot of YEN did not see IOL and only became aware of the close proximity to IOL when they communicated by radio a few minutes later on the Scone CTAF frequency.


The pilot of IOL held a Commercial pilot licence (aeroplane), with a total aeronautical experience of 4,600 hours, and 325 hours on the Bonanza. The pilot of YEN held a Private pilot licence (aeroplane), with a total aeronautical experience of 240 hours, and 107 hours on the Bonanza.


There was no requirement for either aircraft to be equipped with a radio when operating in G airspace in VMC below 5,000 ft. However, the Aeronautical Information Publication (AIP) Enroute (ENR) section stated that:

Pilots of radio-equipped VFR aircraft must listen out on the appropriate VHF frequency and announce if in potential conflict. Pilots intercepting broadcasts from aircraft in their vicinity which are considered to be in potential conflict with their own aircraft must acknowledge by transmitting own call-sign and, as appropriate, aircraft type, position, actual level and intentions.

Both aircraft were radio-equipped. The pilot of IOL had been monitoring the relevant flight information frequency so was alerted to the presence of the other aircraft. The pilot of YEN had not been monitoring the relevant flight information frequency so could not be alerted by ATS if the aircraft was in range, nor could he have been alerted by other aircraft in the vicinity on the area frequency, even if they were operating below 5,000ft.


Both aircraft were equipped with a transponder that was selected to Mode C. This equipment enabled air traffic control to be aware of the location and altitude of each aircraft.

 Flight crew of aircraft equipped with a collision avoidance system are provided information about nearby traffic, based on received information from transponder-equipped aircraft operating on Mode C. This system works whether the aircraft are inside or outside ground-based radar coverage.

IOL was equipped with a portable collision avoidance system (PCAS). The pilot reported that he had switched off the PCAS when flying over Ravensworth coal mine, because the ground based transponder-equipped mining machinery provided many spurious and irrelevant signals to the PCAS. 


The Brisbane Centre ATS does not by default provide a traffic information service to VFR aircraft in Class G airspace. If ATS had not provided traffic information then it is likely that neither pilot would have been aware of the other.

By itself, the concept of unalerted ‘see-and-avoid’ is far from reliable. It is important that pilots apply the principles of ‘see-and-avoid’ in conjunction with an active listening watch. Research has shown the effectiveness of a search for other traffic is eight times greater under alerted circumstances than when un-alerted.

Although the aircraft came into close proximity in airspace where separation is based on visual separation, the probability of a mid-air collision was significantly reduced by the alerting broadcast from ATS that alerted one pilot shortly before the closest point of approach.

The risk would have been further reduced if both pilots had been monitoring the correct en-route frequency, which would have enabled them to be alerted by regular broadcasts from both ATS if it was in radio range, as well as from the other aircraft in the area.


Source: ATSB


AO-2011-121: VH-IOL / VH-YEN, Aircraft proximity event

Date and time: 26 September 2011, 1142 EST

Location: 26 NM (49 km) SE of Scone Aerodrome, New South Wales

Occurrence category: Serious incident

Occurrence type: Airprox event

Aircraft registration: VH-IOL / VH-YEN

Aircraft manufacturer and model: Beech Aircraft Corporation Bonanza A36 / Beech Aircraft Corporation Bonanza A36

Type of operation: Aerial work / Private VH-IOL

Persons on board:


Crew – 2                        Passengers –0


Crew – 0                        Passengers – 0


Persons on board:

Crew – 1                        Passengers – 3


Crew – 0                        Passengers – 0

Damage to aircraft: Nil

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