This subject was on the Agenda of a recent IFALPA ATS Study Group meeting and it was felt by the IFATCA observers present that it may be wise for IFATCA to consider the problem. This paper discusses the problems which currently exist both in the air and on the ground and proposes the establishment by IFATCA of its own policy on the subject aimed at eliminating these problems. The objective is a joint approach with IFALPA to ICAO to seek the amendment of ICAO documentation to implement the proposed new policy.

It should be made clear from the start that the intention of this paper is not to stop the practice of collapsing two or more ATC operating positions into one operational position but rather to provide policy on the mechanics of dealing with R/T communications under the following conditions :

1. Collapsed operating positions with VHF/UHF mix;
2. Collapsed operating positions with two or more VHF frequencies for coverage or administrative reasons;
3. Non-collapsed operating position with VHF/UHF mix;
4. Non-collapsed operating position with two or more VHF frequencies for coverage or administrative reasons.

Where two or more RTF channels are used at an ATC operating position the controller receives messages transmitted on each channel either as a combined output on a single head-set or speaker or as separate outputs on head set/speakers. As a general rule the controller transmits messages on all channels, rather than only on the frequency used by the aircraft addressed. There are very good operational reasons for so doing – examples being that he may not know which channel a particular aircraft is using, combined transmissions effectively prevent aircraft on other channels trying to pass messages while the controller is transmitting and the selection and deselecting of individual keys to transmit messages on different channels increases workload and the likelihood of error. Obviously confusion to both controllers and pilots is the main problem and may therefore lead to a potentially unsafe situation. Some examples of this are as follows;

Simultaneous receipt of transmissions on different frequencies by controllers. This can lead to inaccurate acquisition of essential data. The problem may be compounded by the requirement to use the phrase ‘ say again’ thereby causing another set of simultaneous transmissions. All this may lead to increased R/T loading and/or confusion of data.

Confusion may be caused by a pilot on one of the frequencies believing that the controller, who in transmitting simultaneously on all frequencies, has not received a reply from an aircraft on another frequency. Under these conditions the pilot may in an endeavour to help may try to establish a relay to the aircraft who he thinks has not replied. This could cause excessive R/T with the subsequent increase of traffic loading and the possibility of confusion due to the simultaneous transmissions on the various frequencies. It may be argued in the above case that the controller does not need to have all frequencies selected as he transmits. However, say for example an emergency occurred and a rapid transmission was required then valuable thinking /response time could be wasted by the selection/deselecting of the appropriate switching equipment.

There are two ways in which these sort of problems can be resolved.

Organisational solution

In a totally VHF environment, provided the coverage is adequate, only one RTF channel should be designed for, and used by, any one ATC operating position. This would require appropriate NOTAM action.

Technical solution

If such single channel operation is not practicable, for example in a combined VHF/UHF environment, a technical solution should be implemented through the provision of ‘talk through’ facilities. With such a system all RTF receive/transmitter stations used by an ATC operating position have to be coupled in such a way that messages received from aircraft on any one frequency are automatically and immediately re-transmitted on the other channels. This replicates single channel operation. The system is technically feasible and has been used in the UK for combined VHF/UHF channel working by ACC sectors. The costs are more than offset by the controller staff savings achieved by the collapsing of operating positions.

To conclude

The controller’s task will be made much easier and safer if the requirement to monitor several frequencies simultaneously is removed. It is believed that the advantages gained by the reduction of workload and the possibility of confusion caused by simultaneous receipt of two or more messages far outweigh any disadvantages caused by economic or technical problems.

It is recommended that :

No controller should operate more than one RTF channel unless suitable ‘talk-through’ facilities exist, permitting all users of any of the combined frequencies to hear all transmissions on any of those frequencies. When it is necessary for two or more ATC operating positions to be merged for control from a single operating position, one VHF radiotelephony channel shall be designated for the operating position; except that, if frequency coverage difficulties arise with the designated channel, additional channels may be allocated provided that suitable ‘talk- through’ facilities exist permitting all users of any of the combined channels to hear all transmissions on any of those channels.

It is suggested that if the draft recommendations are approved by Conference a joint IFATCA/IFALPA representation to ICAO should be made, as we have done in the past, for example on the R/T phraseology paper, with a view to amending ICAO documentation on this subject.