The paper investigates the possible reduction in frequency congestion using the introduction of alternative procedures for aircraft initial calls to ATC units.

1.1  Frequency congestion is a significant problem for many ATC units and can reduce the efficiency of the airspace, or in some cases present a safety issue.

1.2  For units with a high ‘throughput’ of traffic, (i.e. many aircraft each handled for short periods), such as approach, director, ground, or tower, the initial call by aircraft has a significant impact on the congestion of the frequency. Evidence suggests it is reasonably common to have an aircraft making an initial call either interrupt a dialogue between a controller and pilot, or have a transmission ‘blocked’ (simultaneous transmissions) – requiring the repetition of the transmissions (European Action Plan for Air Ground Communications Safety, Eurocontrol 2006. Page 6).

1.3  There are existing ICAO procedures, and various alternative implementations globally that provide for the abbreviation or omission of the initial call under certain circumstances, to reduce frequency congestion.

1.4  During the Second Working Group meeting of the ICAO Air Traffic Management Operations Panel (ATMOPSP), in October 2015, the member from the United States presented a paper highlighting the discrepancies with various implementations of the use of MONITOR compared to the ICAO definition of the phrase, including datalink communications. After some discussion it was suggested the Panel could seek the view of the IFATCA membership on the matter and thus the outcomes of this paper will be presented at the next ATMOPSP meeting in April 2016 (Meeting Report, Second Working Group Meeting, ICAO Air Traffic Management Operations Panel, Dubai, UAE, 4-8 October 2015).

1.5  This paper will analyse all the available options, review any discrepancies in globally harmonised implementation, and recommend further action where appropriate.

2.2 Paragraph 5.2.1.5.8 of Annex 10, Vol II defines the meaning for certain terms to be used in communications, the relevant terms are:

2.9.1 CONTACT means for the aircraft to change frequency and initiate communications with another unit. In this case the aircraft must specify:

a)  Station callsign

b)  Aircraft callsign (incl. Heavy if applicable)

c)  Level (and passing level)

d)  Speed (if assigned)

Additional elements may be introduced by the ATS authority, and in some cases elements may be omitted (such as level) provided that appropriate safety work has been conducted and the necessary alternative procedures are in place.

2.9.2 MONITOR means to listen on the advised frequency for a broadcast; normally ATIS or weather information. It is implied that this is in addition to the primary frequency, and does not appear to be intended for regular communication channels.

2.9.3 STAND BY FOR means to change frequency, but do not initiate contact; wait and the ATS unit will contact you shortly.

2.10. Depending on the unit in question, some of the information that is required to be included in the initial call is usually redundant.

2.10.1.  For instance, an approach sector will generally issue a lower level on first contact, therefore the requirement to include a ‘cleared level’ in the transmission (as a cross check) is questionable, as it will usually immediately change. In cases where a new level is not assigned, local procedures could require that the controller reissue the level to the pilot rather than the opposite – this would seem a more efficient option.

2.10.2.  Other information such as HEAVY/SUPER could be considered redundant where the controller display clearly highlights this to the controller, however this would have to be a consideration depending on local implementation. Similarly, Mode S downlink information has the capacity (where equipped) to provide information in a more efficient manner than verbally from the pilot, in this particular case; level and speed information. Although existing procedures in most places to for allow for this.

2.11.  In any case, there is clearly an opportunity to reduce the content of the initial call in certain circumstances. There are some existing ICAO procedures to achieve this, and also variations of such that have been implemented at a local level.

2.12.  There are known alternative implementations of CONTACT, specifically the use of CONTACT WITH CALLSIGN ONLY in several locations (London, Amsterdam, Dubai, Madrid, Frankfurt, Munich, Zurich (All except Amsterdam are reports from local controllers, January 2016. Details available is required)) which attempts to minimise the disruption of the CONTACT call, but retains the confirmation that the frequency transfer has successfully been conducted. However, as there is no internationally recognised version of this procedure some confusion is known to exist in the pilot community (Professional Pilots Rumour Network- www.pprune.org, forum threads 240735, 340899, 368254, 518524, 552171. 7 January 2016).

(The Netherlands AIP – Implementation of Callsign Only, AIP, The Netherlands, Eff. 7 January 2016. Part 3 Aerodromes (AD) AD 2.22 para 2.4.5.4)

2.13.  The other options (MONITOR and STAND BY FOR) do not immediately provide confirmation that the aircraft has successfully selected and switched to the correct frequency. In the event that this has not occurred, there are may be delays encountered, and in some cases safety implications where aircraft are operating in high density airspace. While there are existing procedures to cater for the instance when communication transfer has failed, in some circumstances it is preferable to have confirmation built into the procedure.

2.14.  The MONITOR instruction, while it appears to be intended for broadcast information, is known to be used in multiple locations by towers as a transfer instruction, and by oceanic units when referring to HF frequencies for SELCAL watch.

2.15.  In reference to the use on the ground, the known implementations consist of either the verbal instruction to MONITOR GROUND or aerodrome signage instructing aircraft to MONITOR TOWER (freq). While the intention is clear, and the potential for any misunderstanding is minimal, it appears that the correct phraseology that should be used in this case is in fact STAND BY FOR (unit) ON (freq). As these implementations include the use of fixed aerodrome signage, any consideration on amending the phraseology will necessitate the expense of amending signage.

3.1.1 Where the standard CONTACT transmission is considered too verbose for the receiving unit, the existing alternative STAND BY FOR should provide an improvement in frequency and workload management. It does not however provide confirmation that the transfer has occurred. Where this confirmation is desirable, the CALLSIGN ONLY procedure has been introduced in several regions. Locations that utilise this procedure seem to be pleased with the result. It would be beneficial for global harmonisation if there was an ICAO procedure defining CALLSIGN ONLY to be used in lieu of local procedures.

3.2 The existing ICAO definition for MONITOR is appropriate, and should generally be used to refer to broadcast information or other channels where an actual dialogue of communication will not normally take place. Such examples are ATIS, AWIS, 121.5.

3.2.1 There are implementations of MONITOR in some locations – generally towers – that are inconsistent with the ICAO definition, and would be more appropriate as STAND BY FOR. It would simplify global harmonisation if these implementations were changed to STAND BY FOR, however it is recognised that in some locations this would require the replacement of existing aerodrome signage at a cost.

3.2.2 The use of CPDLC had encouraged the use of MONITOR in the oceanic environment, usually when referring to HF frequencies. In consideration of the limitations of amending the CPDLC message set, and the nuances of HF SELCAL watch, it is not considered feasible or practical to correct the use of the term in this environment.

It is recommended that:

4.1. The Executive Board urge ICAO to consider:

a)  A globally standardised “CALLSIGN ONLY” procedure.

b)  Clarification and global harmonisation of MONITOR and STAND BY FOR.