On 31 August 2015, the pilot, and sole occupant, of a Schweizer 269C helicopter, registered VH JXO (JXO), was conducting aerial spraying in the Edinburgh area, South Australia. At about 1503 Central Standard Time, a military Lockheed AP-3C aircraft (Orion) was about 15 NM northeast of Edinburgh, at 6,500 ft, tracking for the runway 18 instrument landing system (ILS) approach to Edinburgh Airport. 

At about 1504, the pilot of JXO called Edinburgh Tower air traffic control, and requested a clearance to track to ‘Clare’ (Clare Valley), South Australia. The tower controller mistook the pilot’s request to ‘Clare’ for ‘Calvin Grove’, and cleared the pilot of JXO to track direct to Edinburgh Tower. The pilot complied with the instruction, even though this was not the clearance expected. However, being new to the area and concerned about the direction of the clearance, the pilot attempted to contact their company via UHF radio to ask for advice.

At about 1512, the Orion was passing 2,400 ft, on a 6.5 NM final and travelling at 170 kt. JXO was at 600 ft and travelling at 60 kt. Based on the expected tracking of the three aircraft, the tower controller assessed that JXO would safely cross the runway centreline in front of the Orion. Consequently, the tower controller cleared JXO to track to Calvin Grove. The pilot heard the call but their radio was still selected to transmit on UHF not VHF, so the controller did not receive a response. The pilot misheard the clearance, and turned right to track northwards to Clare Valley.

Having not received a response, the tower controller made several further attempts to communicate with the pilot of JXO, without receiving a response. The pilot of JXO could hear the calls and eventually realised they had the incorrect radio selected to transmit.

When the Orion and JXO were about 1.5 NM apart, and their flight paths were merging, the tower controller then conducted another radio check. The pilot of JXO responded, advised they had the radio selected to an incorrect frequency, and that they had requested a clearance to track to Clare Valley, not Calvin Grove. During that transmission, the distance between JXO and the Orion reduced to about 1 NM laterally, and 200 ft vertically.

Immediately following the pilot of JXO’s response, the tower controller asked whether the pilot had the ‘P3’ (Orion) in sight. The pilot soon sighted the Orion and responded having the aircraft in sight. The tower controller directed the pilot to pass behind that aircraft. The pilot of JXO had immediately initiated a climb to avoid a collision, and estimated the Orion passed about 100 ft below. The crew of the Orion sighted JXO, and increased the rate of descent to pass beneath the helicopter. The Orion crew estimated that JXO passed about 50 ft directly above the Orion, and were concerned it may collide with the aircraft’s vertical tail fin. 

The Orion landed without further incident on runway 18. The pilot of JXO was subsequently cleared to depart the Edinburgh control zone tracking to Clare Valley.

This incident highlights the importance of communication, and demonstrates the potential consequences of a loss of communication. Whether pilots are communicating with each other, or with air traffic control, it is essential to understand what is being said and how that potentially affects them. In particular, if an instruction from air traffic control is not as expected, pilots should request clarification.


Aviation Short Investigations Bulletin - Issue 45

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