Occurrence Summary
On four occasions in three months, pilots from the same local company have reported difficulties communicating on the Whyalla MBZ frequency with the flight crews of one particular RPT operator. Following these incidents, the local company raised the following concerns:
(1) crews of the RPT aircraft do not always provide an initial taxy call on the MBZ frequency when preparing for departure from Whyalla;
(2) crews of the RPT aircraft appear to change to the Whyalla MBZ frequency at approximately 10 NM rather than the required 15 NM; and,
(3) crews of the RPT aircraft are often not contactable on the MBZ frequency following an initial inbound broadcast at 25 NM from Whyalla.
The RPT operator's standard operating procedure required crews to monitor the MBZ frequency within 25 NM of Whyalla. Any company calls were to be completed during cruise and not during the approach and arrival phases. The aircraft were equipped with dual VHF radios so that a continuous listening watch was maintained on both the MBZ and flight service frequencies. The report to flight service that the crew were switching to the MBZ frequency was a formality and indicated that this was the prime frequency for communication during the arrival and departure.
The pilot of the RPT aircraft recalled that, on 19 December 1997, all the standard reports and broadcasts were given. He also recalled that a pilot of one aircraft in the area was referring to the company name and not the aircraft's specific identification. This did not immediately attract the pilot's attention because the flight number was not specifically mentioned and several aircraft of the same company were operating in the area at the time.
The airspace around Whyalla can be congested at certain times with the arrival and departure of several aircraft as well as local aircraft operating in the area. It is not uncommon for radio communications to be overtransmitted as appeared to have occurred in one of the reported incidents. There were also a number of nearby CTAFs which utilise the same frequency as the Whyalla MBZ, which adds to the communication congestion.
Safety Action
Representatives from both the companies, as well as from CASA, met in order to clarify the circumstances of the incidents and to resolve any outstanding concerns about operations in the MBZ at Whyalla. The trial of flight numbers for aircraft callsigns was discussed. It was agreed that flight numbers did not provide any information as to the aircraft type, and therefore its performance and flight profile. It was later clarified that the RPT operator, as with all operators who participated in the trial, was no longer bound to continue to use flight numbers as callsigns.
It was proposed to change the Whyalla MBZ to a discrete frequency as many aerodromes in the local area used the same frequency (126.7 MHZ). The Adelaide office of CASA supported the proposal.
Both companies expressed a willingness to be flexible with aircraft tracking and aircraft operation during climb and descent to facilitate operations within the MBZ.